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 Permanent Link:
 http://ufdc.ufl.edu/AA00009052/00001
Material Information
 Title:
 Singular dynamics in quantum mechanics and quantum field theory
 Creator:
 Zhu, Chengjun, 1963
 Publication Date:
 1994
 Language:
 English
 Physical Description:
 vii, 103 leaves : ill. ; 29 cm.
Subjects
 Subjects / Keywords:
 Adjoints ( jstor )
Boundary conditions ( jstor ) Diseases ( jstor ) Equations of motion ( jstor ) Mathematics ( jstor ) Modeling ( jstor ) Quantum field theory ( jstor ) Quantum mechanics ( jstor ) Symptomatology ( jstor ) Trajectories ( jstor ) Dissertations, Academic  Physics  UF Physics thesis Ph.D Quantum theory ( lcsh ) Singularities (Mathematics) ( lcsh )
 Genre:
 bibliography ( marcgt )
nonfiction ( marcgt )
Notes
 Thesis:
 Thesis (Ph. D.)University of Florida, 1994.
 Bibliography:
 Includes bibliographical references (leaves 101102).
 General Note:
 Typescript.
 General Note:
 Vita.
 Statement of Responsibility:
 by Chengjun Zhu.
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 University of Florida
 Holding Location:
 University of Florida
 Rights Management:
 Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for nonprofit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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31920351 ( OCLC ) AKF8490 ( NOTIS )

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Full Text 
SINGULAR DYNAMICS
IN
QUANTUM MECHANICS AND QUANTUM FIELD THEORY
By
CHENGJUN ZHU
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1994
SINGULAR DYNAMICS
IN
QUANTUM MECHANICS AND QUANTUM FIELD THEORY
By
CHENGJUN ZHU
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
Dedicated to
My Parents and Friends
ACKNOWLEDGMENTS
I wish to thank my supervisor, Prof. J. R. Klauder, for his efforts, patience
and encouragement throughout the time I have been at the University of Florida.
He introduced me to most of the topics involved in this dissertation and always
was ready for a discussion if needed. Over the years, his enthusiasm and
encouragement have been constant sources of inspiration to push the project
forward.
I am grateful to the other members in my supervisory committee, Prof.
Pierre Ramond for his valuable comments and suggestions, Prof. Charles
Hooper, Prof. Robert Buchler, Prof. David Tanner and Prof. Christopher Stark,
for patiently sitting through my oral exam and thesis defense. Special thanks
should go to Prof. Buchler for his kindness, concern and heuristic suggestions
when I was very depressed in jobhunting.
Also I want to express my deep thanks to my fellow graduate students
and colleagues, for their help and encouragement throughout the years.
TABLE OF CONTENTS
pages
ACKNOWLEDGMENTS in
ABSTRACT vi
PART I CLASSICAL SYMPTOMS OF QUANTUM ILLNESSES
CHAPTERS
1 INTRODUCTION 2
1.1 Basic Concepts of Operator Theory 3
1.2 Symmetric Operators and Extensions 4
1.3 The Construction of SelfAdjoint Extensions 8
2 CLASSICAL SYMPTOMS OF QUANTUM ILLNESSES 10
2.1 Principal Assertions 10
2.2 Classical Symptoms of Quantum Illnesses 12
2.3 More General Examples 16
2.3.1 Examples of OneDimensional Hamiltonians 16
2.3.2 Examples of ThreeDimensional Hamiltonians 20
3 SELFADJOINTNESS OF HERMITIAN HAMILTONIANS 22
3.1 Three Different Cases of Hermitian Hamiltonians 22
3.2 The Application of Boundary Conditions and SelfAdjoint
Extensions at Regular Points 32
3.3 The Application of Boundary Conditions and SelfAdjoint
Extensions at Singular Points 34
3.4 Conclusion 38
PART II OPERATOR ANALYSIS AND FUNCTIONAL INTEGRAL
REPRESENTATION OF NONRENORMALIZABLE MULTI
COMPONENT ULTRALOCAL MODELS
4 INTRODUCTION 44
5 CLASSICAL ULTRALOCAL MODEL AND THE STANDARD
LATTICE APPROACH 48
6 OPERATOR ANALYSIS OF MULTICOMPONENT ULTRALOCAL
MODELS 53
IV
6.1 Operator Analysis of SingleComponent Ultralocal Models
54
6.2 Operator Analysis of FiniteComponent Ultralocal Fields
60
6.3 Operator Analysis of Infinitecomponent Ultralocal Fields
65
7 THE CLASSICAL LIMIT OF ULTRALOCAL MODELS 73
7.1 Ultralocal Fields and Its Associated Coherent States 74
7.2 Selection of the Coherent States for Ultralocal Fields
and the Classical Limit 77
8 PATHINTEGRAL FORMULATION OF ULTRALOCAL MODELS
86
8.1 Operator Solutions of Ultralocal Models 87
8.2 EuclideanSpace PathIntegral Formulation of
SingleComponent Ultralocal Fields 92
8.3 EuclideanSpace PathIntegral Formulation of
MultiComponent Ultralocal Fields 96
REFERENCES 101
BIOGRAPHICAL SKETCH 103
v
Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
SINGULAR DYNAMICS
IN
QUANTUM MECHANICS AND QUANTUM HELD THEORY
By
Chengjun Zhu
April, 1994
Chairman: Dr. John R. Klauder
Major Department: Physics
The classical viewpoint that the pathologies of quantum Hamiltonians are
reflected in their classical counterparts and in the solution of the associated
classical dynamics is illustrated through the properties of classical equations of
motion. Rigorous mathematical proofs are provided by calculating the
deficiency indices, which further help to analyze the possibility of extending the
Hermitian Hamiltonian to a selfadjoint one. A few examples of how to add
boundary conditions on wave functions in order to have selfadjoint extensions,
as well as to cure the illness of certain Hamiltonians, are discussed.
The nontrivial (nonGaussian), nonperturbative quantum field theory of
0(N)invariant multicomponent, nonrenormalizable ultralocal models is
presented. An indefinite nonclassical and singular potential has replaced the
nonvanishing, positivedefinite nonclassical and singular potential appeared in
the singlecomponent case. The operator theory of multicomponent ultralocal
vi
fields remains noncanonical even with the disappearance of the singular
potential. The validity of this nontrivial solution is supported by the fact that the
nontrivial quantum solution reduces to the correct classical theory in a suitable
limit as fi 4 0. The nontrivial (nonGaussian) path integral formulation
constructed by the nonperturbative operator solution, involving the nonclassical
and singular potential, replaces the standard lattice approach, which invariably
leads to a Gaussian theory regardless of any nonlinear interactions. The
appearance of the nonclasssical, singular potential suggests that we can not
always place the classical Lagrangian or classical Hamiltonian directly into the
pathintegral formulation, or in other words, a straightforward canonical
quantization of fields with infinite degrees of freedom does not always apply.
These differences suggest plausible modifications in the latticespace formulation
of relativistic nonrenormalizable models that may lead to nontriviality for N
4
component models such as On, n > 5 (and possibly n = 4), for N > 1.
Vll
PARTI
CLASSICAL SYMPTOMS
OF
QUANTUM ILLNESSES
CHAPTER 1
INTRODUCTION
The rules of quantization, as laid down in 1926 by Schrodinger, have stood
the test of time and have provided the basis for applying (and teaching)
nonrelativistic quantum mechanics1. Because of the overwhelming success of the
theory, it is not surprising that physicists have little use for several mathematical
niceties that go by the largely unfamiliar code words of "selfadjoint extension,"
"deficiency indices," operator domains," etc. (which we will briefly define in
subsequent sections). 2/3
These concepts typically become important when the quantization
prescriptions are ambiguous or otherwise incomplete all by themselves4. Our
goal is to show that such quantum technicalities are actually reflected in the
classical theory by corresponding difficulties that are easy to see and understand.
It will be clear that such an evident classical difficulty must lead to some kind of
quantum difficulty, and thus the naturalness of the corresponding quantum
technicality will become apparent. We may go so far as to assert that there are
sufficient classical symptoms of any quantum illness that a complete diagnosis is
possible already at the classical level (Chapter 2). Of course, resolving the
problems and effecting a full cure, when one exists, can only take place at the
quantum level (Chapter 3).
This chapter contains basically a summary of the mathematical concepts
and theorems prepared for later chapters. In Chapter 2, we will discuss the
properties of classical solutions of given examples, whose "symptoms" can be
2
3
used to diagnose any potential quantum "illnesses". In Chapter 3, we will
provide the mathematical proof for all the assertions made in Chapter 2 and will
also give a few examples of how to add boundary conditions on the wave
functions in order to extend the Hamiltonians to be selfadjoint and so to cure the
illness of certain Hamiltonians.
1.1 Basic Concepts of Operator Theory
In this section we follow Ref. 3 closely. The operators we deal with in
quantum mechanics are frequently unbounded operators which need to be
defined on a domain D(A) to ensure that Ay/e for y/ e D(A), where is
Hilbert space.
Generally, if A and B are two unbounded linear operators,
a,P e C,
y/e D (ocA + pB).
D (aA + pB) = D(A) n D(B),
(aA + pB)y/ = a (A y/) + p(B y/),
For the product put
D(AB) = {y/:y/eD(B), By/ eD(A)},
(AB)y/= A (By/), y/e D (AB).
In general D(AB) D(BA), and hence AB BA, and even A A'1 A'1 A,
because their domains may not coincide. So extra care is needed in treating these
operators.
4
We recall that A is densely defined in #if (and only if) jtfis the closure of
D(A), i. e., for y/ e there is a sequence of elements of D(A) converting to y/,
[fa +y/f fa e D(A)].
For a densely defined operator A for iH into there exists a unique
adjoint operator A+ which satisfies
(A yi,
where y/ e D(A) and 0 e D{A +).
If an adjoint operator A+ = A on D(A), and D(A) = D(A+), then A is called
a selfadjoint operator.
1.2 Symmetric Operators and Extensions
If A+ = A on D(A), then D(A) Â£ D (A*) always holds (like Hermitian
Hamiltonian operators). Now,
(a) A is called a selfadjoint operator when D(A) = D(A+), and one writes A = A+.
(b) A is called a symmetric operator when D(A) c D(A+), and one writes A c A+.
Further, if there exists a symmetric extension As of A, such that A c As =
As+ c A+, then we say that A has the selfadjoint extension As (by enlarging D(A)
to D(AS) and contracting D(A+) to D(AS+) = D(AS)).
Let A + 0= i 0t, with solutions Q e N which are closed subspaces of ^4
known as the deficiency spaces of A; and their dimensions, n respectively, are
called the deficiency indices. We shall also say for brevity that A has deficiency
indices (n+, n_).
Lemma 1. If A is symmetric, then D(A'1) = D( A )N+N., A denotes the
closure of A.
5
Lemma 2 A symmetric operator with finite deficiency indices has a self
adjoint extension if and only if its deficiency indices are equal.
With the help of the two above Lemmas, the following theorem regarding
deficiency indices is straightforward:
THEOREM 1: Suppose the Hermitian operator A has deficiency indices
(n+, n.), then if
(i) n+ = n. = 0,A is selfadjoint when D(A) is closed and the closure of A is self
adjoint when D{A) is not closed.
(ii) n+ = n 0, A has selfadjoint extensions.
(iii) n+ n., A is not selfadjoint and has no selfadjoint extension.
This theorem is used to classify Hermitian operators, and we see that not all
Hermitian operators will generate fulltime quantum mechanical solutions.
Example: A = id/dx on Li(Q)
A + 0t= z
Ai=i d/dx,
0t(x) ~ exp(+ x).
(a) Q = ( oo, + ): Neither 0+ nor 0. is in o, + oo)r so n+ = n = 0 and A is
selfadjoint on its natural domain. This fact is consistent with its classical
behavior (see Fig. 1(a)), where there is a fulltime evolution.
(b) Q = [ 0, + <>): 0. = exp(x) is not in L([ 0, + >)), so (n+, n.) = (1, 0), A is
not selfadjoint and possesses no selfadjoint extension. This fact is consistent
with its classical behavior (see Fig. 1(b)), where there is no fulltime evolution.
(c) 2 = [ 0,1]: Both 0 are in Â£^([ 0,1 ]), (n+, ru) = (1,1), A has selfadjoint
extensions by adding the boundary condition y/(l) = exp (iff) yKO), where 8e 9.
6
The spectrum of A = 6 + 2n n, n = 0, 1, 2,.... For different 6, we get a different
selfadjoint extension. The case of 6 = 0 is the usual case used in quantum
mechanics and is called the periodic boundary condition. See Fig. 1(c) for its
consistent classical behavior.
The deficiency indices are clearly of central importance in the classification
of Hermitian operators and in the construction of selfadjoint extensions. These
may be found easily if explicit solutions of A fy/ = i \Â¡r are known, but unless
the coefficients of A are simple, the calculations will involve difficult special
functions. In order to avoid those tedious, sometimes even impossible
calculations, we will use a modified theorem of deficiency indices, especially
when both end points of Â£2 are singular. First, let us look at an example with
quantum Hamiltonian H, where
2
H \f/=(p2 + x3)\i/=(^ + x3)y/
dx2
acting on functions defined on an interval 2 = (<,+ ). Both end points x =
are singular. A direct calculation of the deficiency indices seems incredibly
tedious since the behavior of a solution of Hi// = i y/ at both end points must
be known. To simplify the difficulties, we separate Q = (a, b), where a and b are
both singular, to two intervals with Q\ = (a, c ] and Qi = [ c, b), where c is a
regular point. Here comes the second theorem regarding deficiency indices:
THEOREM 2 Let Aa and A\, be symmetric operators associated with A on
2i and / respectively. If n, na, nb indicate the deficiency indices of A, Aa
and Ab respectively, then n= n^ + nb 2, respectively (see Chapter 2 of Ref.
3).
To apply this result to the above example, we have
7
HV
= (Â£ + *3)V4
= I>
Since H is a real operator, i. e., H = H, we have y/. = yr+. So n+= n. and we only
need to consider y/+ and n+. Let y/+ = yr,
(f+ X3)//= 1>
ax2
The asymptotic behaviors at x > 00 is given by
y/ x3y/= 0
1/4^+cc ~ Vx Ki/5(x5/2) ~ x3>'4exp( 1*5/2)
5 5
. ~ VR /l/5(^xf/2) ~ W 3/4COS ( ^W5/2 ^7r)
or
V'f!. ~ VR /s&xj572) ~ W* 3/4sin( Jxj572
A 5 5 20
where Jv, N\ and K\ are the Bessel functions of the first and second kinds,
respectively. Obviously, the integration
jy/(x)j2dx converges at x = +00.
Thus, n+r +00= 1. In the same way,
vÂ£L~w3/4
8
(1 2)
so that both solutions of satisfy
j \Â¡/ixfdx converges at x = 
Therefore, n+ .00= 2, and
n+ n+i +oo + +,. 2 = 1 + 2 2 = 1
(+, n.) = (1,1).
One boundary condition* is needed to extend H to be selfadjoint. The existence
of bound states yioo demonstrates that the energy spectrum is discrete. This
result is exactly what is claimed in Chapter 2.
Later in Chapter 3, we will see examples for three different cases of the
deficiency indices: (i) += n. = 0, (ii) n+= n. 0, and (iii) n+* n..
1.3 The Construction of SelfAdjoint Extensions
Before we construct the selfadjoint extensions, we introduce some
notation (see Chapter 10 of Ref. 3):
(i) [(f), y/) = 04 y/) (0, ,4 V)/ where D(A +);
(h) f\r fi " fn e D(A +)= D{A) N+N_, where fÂ¡ = h{ + fa i= 1,2,...,
hj e D(A), (foeN+0N..
If n+=il. the number of boundary conditions = n+; see page 260 of Ref 3.
9
We call fi, fi fn linearly independent relative to D(A) if fa, fa,..., fa are
linearly independent.
With the help of the preceding definitions, we introduce the following
theorem:
THEOREM 3 Let A be a symmetric operator with finite nonzero deficiency
indices n+ = n.= n. Suppose that f\, f2 / D(/4+) are linearly independent
relative to D(A) and satisfy
(fi,fj)= 0 (1,7 = 1,2, n).
Then the subspace Moi ^consisting of all y/e DiA*) such that (\j/,ft) = 0 (i = 1,2,
n) is the domain of a selfadjoint extension M of A, given by M y/= Afyj for
y/eM.
{yf, fi) = 0 ,i = 1, 2,n, are called the number of n boundary conditions on
the wave function y/.
In chapter 3, we will give a few examples of how to use theorem 3 to
obtain some of these selfadjoint extensions and thereby cure the illness of certain
Hamiltonians.
CHAPTER 2
CLASSICAL SYMPTOMS OF QUANTUM ILLNESSES
Without using the precise definitions and techniques of operator theory,
presented in chapter 1, we can simply show that the pathologies of quantum
Hamiltonians are reflected in their classical counterparts and in the solutions of
the associated classical equations of motion. This property permits one, on the
one hand, to appreciate the role of certain technical requirements acceptable
quantum Hamiltonian must satisfy, and, on the other hand, enables one to
recognize potentially troublesome quantum systems merely by examining the
classical systems.
In Â§2.1, we will make the principal assertions that three categories of
classical solutions correspond to three categories of the selfadjointness of
quantum Hamiltonian operators. Examples are given in Â§2.2 and Â§2.3, while the
mathematical proof will be presented in chapter 3.
2.1 Principal Assertions
H =
V
2m
Specifically, for the classical system with a real Hamiltonian function
+ V(q), the classical equation of motion
mq'(t) = V'[q(t)]
admits two kinds of solution:
(i) q(t) is global (which is defined through  < t < +<) and unique, e. g.,
H = p2 + i?4 ;
10
11
(ii) q(t) is locally unique, but globally possibly nonexistent (escapes to infinity
in finite time). This case may be also divided into two subcases:
extendible (q(t) can be extended to a global solution) or nonextendible.
For example, H = p2 qA, H = p2 q3 are extendible, but H = pq3 belongs
to nonextendible situation.
The corresponding quantum mechanical problem
i/yKx, t) = HyKx, t) = [ //2 d2 + v(x) ] i/Kx, t)
ot 2m dx 2
has similar cases. To conserve probability, the time evolution of the wave
function must be effected by a unitary transformation. A unitary transformation
gives a prescription for wave function evolution for all times t, < t < or as
we shall sometimes also say, for full time. The generator of such a unitary
transformation times V^T, which we identify with the Hamiltonian operator (up
to constants), must satisfy one fundamental property, namely, that of being "self
adjoint." Being selfadjoint is stronger, i.e., more restrictive, than being
Hermitian, which is the generally accepted sufficient criterion. According to
Theorem 1 on page 5, typically, there are three qualitatively different outcomes
that may arise (i) no additional input is needed to make the Hamiltonian self
adjoint; (ii) some additional input (i.e., the boundary conditions) is required to
make the Hamiltonian selfadjoint, and qualitatively different Hamiltonians may
thereby emerge depending on what choice is make for the needed input; and (iii)
no amount of additional input can ever make the Hermitian Hamiltonian into a
selfadjoint operator. Remember it is only selfadjoint Hamiltonians that have
fully consistent dynamical solutions for all time. Thus in case (iii) no acceptable
quantum dynamical solution exists in any conventional sense.
12
Therefore we make the general assertions that there are three categories of
classical solutions, which correspond to three categories of the selfadjointness of
quantum Hamiltonian operators:
Â£(0
Hamiltonian operator
selfadjoint & unique
selfadjoint extensions exist
no selfadjoint H exists
(i) global & unique
(ii) nonglobal but extendible
(iii) nonglobal & nonextendible
2.2 Classical Symptoms of Quantum Illnesses
To be sure, the majority of classical systems one normally encounters~as
represented by their classical Hamiltonians, their Hamiltonian equations of
motion, and the solution to these equations of motionare trouble free. But there
are exceptions, classical systems which exhibit one or another kind of singularity
in their solutions, and it is in these problematic examples that we will find the
anomalous behavior we seek to illustrate.
Let us consider three model classical Hamiltonians that will exhibit the
three kinds of behavior alluded to above.
Example a:
H = p ^ 4.
2y 41
The equations of motion lead to
i2 = 2Efr,
13
where E > 0 is the conserved energy. Nontrivial motion requires E > 0 and E >
94/4 in which case
leads to a welldefined, unique solution valid for all time. This solution exhibits
a periodic behavior with an energy dependent period T(E). See example a in
Table I.
Example b:
H=2p2 + 3
The equations of motion lead to
42 = 2 E
and E can assume any real value. Since cp < 3E, we find that

da
^ t + c.
J
This solution has the property that q diverges, <7 for finite times, for
any nonzero E; see the solid line of example b in the table. The indicator of this
behavior is the observation that the integral converges as the upper limit goes to
 00 leading to a finite value for the right side, namely, a finite value for the time.
Actually, this same trajectory diverges at an earlier time as well. As b illustrates,
14
the particle comes in from q = o at some time, say t = to, and returns to q =  at
a later time, say T + to, where
0E)'/3
dq
T = 2
For any nonzero E, T < in particular, by a change of variables, we learn that
where S(E) = E/ IEI, the sign of the energy. As I EI  0 the particle spends more
and more time near q = 0, until, at E = 0, it takes an infinite amount of time to
reach (or leave) the origin.
Example b in the table illustrates the generic situation for E 0 and finite
T. How could one possibly expect the quantum theory to persist for all time
when the generic classical solution diverges at finite times? The only possible
way for this example to have a genuine quantum mechanics is for the particle to
enjoy a fulltime classical solution. And to achieve thatand this is the important
pointwhenever the particle reaches q = o, we must launch the particle back
toward the origin with the same energy, once again follow the trajectory inward,
and then outward, until the particle again reaches q = <, when we must again
launch the particle back toward the origin with the same energy,..., and so on,
both forward and backward in time ad infinitum. In brief, to get fulltime classical
solutions (as needed to parallel full time quantum solutions) we must recycle the
15
same divergent trajectory over and over again in an endless periodic fashion
(with period T(E)); see b in the table with the solid and the dashed lines.
Example c:
H = p cj3.
The equations of motion, in this case, lead to
4 =
with the solution
q(t)= l/Yc21.
The solution is valid for t < c/2, diverges at t = c/2, and becomes imaginary for t >
c/2. See example c in the table, where we chose the constant c = 0. In no way can
an imaginary solution be acceptable as a classical trajectory. We cannot relaunch
the particle once it has reached c\ = at t = c/2 following the kind of solution
we have found, the only solution there is, as we were able to do in case b. In
short there is no possibility to have a fulltime classical solution in the present
example.
If there is no fulltime classical solution, then there should be no fulltime
quantum solution, and that is exactly what happens. The corresponding
quantum Hamiltonian may be chosen as Hermitian, but there are no technical
tricks that can ever make it selfadjoint. Once again, the signal of this quantum
behavior can be seen in the classical theory, i.e., a divergence of the classical
16
solution followed by a change of that classical solution from real to imaginary.
With such a classical symptom, it is no wonder that there is an incurable
quantum illness.
2.3 More General Examples
In what follows we discuss a number of hypothetical classical
Hamiltonians, examine qualitatively the nature of their classical solutions, and
address, based on the thesis illustrated in Sec. 2.1, the problem of making an
Hermitian Hamiltonian into a selfadjoint one, if that is indeed possible.
Let us dispense with the "healthy" cases at the outset. Whenever the
classical equations of motion admit global solution for arbitrary initial conditions,
then the quantization procedure is unambiguous (apart from classically
unresolvable factorordering ambiguities). Observe that the existence of such
global solutions is an intrinsic property of a Hamiltonian independent of any
particular set of canonical coordinates.
2.3.1. Examples of OneDimensional Hamiltonians
4 = p = 2 VE + q4,
= t +c.
Example d:
17
E can be any real value.
For E > 0, we notice that dq / 2 VE + qA converges to, say T (E), which
means when the particle travels from to + the time interval is T (E). For
nonzero E, T is finite; see the solid line of example d in the table. In order to get a
fulltime classical behavior, we must send the particle back when it gets q = o;
see the two distinct dashed lines of d in the table. In quantum theory, this
situation corresponds to adding two boundary conditions (at q = ), which are
required to extend H to be selfadjoint.
For E < 0, the paths do not cross the origin, but there is no essential
difference in the quantum behavior from the case E > 0. That means we still need
to add two boundary conditions to extend H to be selfadjoint.
Example e:
h=2v2q2'
q=p = il jE + ql,
(1/2) In  q + Vi/2 + E  = f + c.
When the particle travels from > to + the time spent by the particle spans the
whole faxis (see example e in the table), so there is a global solution for an
18
arbitrary initial condition. Thus the quantum Hamiltonian is unique and self
adjoint.
Since there is no periodic behavior, the spectrum of the quantum
Hamiltonian is continuous.
Example f.
H = 2pcj2,
2cj = l/(t + c).
Global solutions exist (see example / in the table) and the quantum Hamiltonian
is selfadjoint. Since there is no periodic behavior the spectrum is continuous.
Example g:
H =2p (1/q),
consider Q = ( <*>, 0) or (0, + ),
4 = 2(1 /q),
q2 = 4t + c.
19
similar to Example c, q becomes imaginary for t < c /4, and there is no
possibility of having a fulltime classical solution, just as in the case of example c.
Therefore there is no way to extend the Hamiltonian to be selfadjoint.
Example h:
H = p2 + 2 p q3,
q = 2(p + q3) = 2 Jq6 + E.
Its classical solution is similar to example d, and is identical to H = p2 q6' to
which it is canonically equivalent.
Example i:
H = p2 + 2p /q
q 0, so Â£2 = ( <*>, 0) or (0, + <),
q=2(p + \/q) = 2 jE + l/q2,
Vl +Eq2 = 2 E(t+c).
The solution to the motion reads
(2E)\t + c)2 E q2 = 1.
20
See example i in the table, where we chose E > 0. Since q = 0 is a singular point,
we divide SR into Q = ( <*>, 0) and (0, + <*>). For example, when the particle reaches
q > 0+, we have to send it back or cross over q = 0 to get a fulltime classical
behavior. By choosing c, the fulltime classical picture may be like the solid and
dashed lines of i in the table. In quantum theory, one boundary condition is
needed to extend H to be selfadjoint.
Two additional examples (/ and m ) appear in the table without discussion
in the text.
2.3.2. Examples of ThreeDimensional Hamiltonians
To simplify the problem, we consider here only central potentials V{r). In
suitable units, the quantum Hamiltonian becomes
H = V2 + V(r),
v2_ 1 dr?d L2
r2dr dr r2
Set
V/,
then
Hr = + ^4^ + V{r) for u(r).
dr1 r
The condition that i l\yl2 d3r converges now becomes the condition that
Qu(r)fdr converges.
For V(r) = A /rn, n = 1,2,3,..., A >0,
21
Hr = Pr2a /rn) + (/ (/ + l)/r 2)
and the classical equation of motion is
r = 2VE + U/r")(/ (/ + l)/r2).
Under both cases of E < 0 and E > 0, we see the difference between = 1 and
n >2. For n > 2, near the origin, i.e., r ~ 0, f = 2 E + A /r", so r could go as near
as r ~ 0. See example k in the table. In quantum theory, one condition is
required to extend the Hamiltonians to be selfadjoint. It corresponds to one
parameter (e.g., see parameter B in Ref. 4), which is needed to specify quantum
solutions. But for n= 1, f = 2Ve + A /r (/ + l)/r2; with E < 0 and / > 0, the
motion oscillates between the two roots of the expression under the radical,
namely,
/(/+!)
E
1(1+1)
E
So it avoids the singular point r = 0, and therefore it has a fulltime classical
evolution (see example j in the table), thus its quantum Hamiltonian is a self
adjoint operator. That is why the hydrogen atom does not have any problems.
CHAPTER 3
SELFADJOINTNESS OF HERMITIAN HAMILTONIANS
Having recalled that simple and physically natural classical "symptoms"
are available to diagnose any potential quantum "illness," we now discuss some
of the standard techniques in Chapter 1 used to analyze Hamiltonian operators
and confirm that the classical viewpoint presented in Chapter 2 is fully in
agreement with conventional analyses.
In particular, we analyze in this chapter the selfadjointness of several
Hamiltonians which appeared in Chapter 2 by calculating their deficiency
indices directly. Therefore, we can verify the consistency of solutions of classical
and quantum Hamiltonians. According to Theorem 1 on page 5, we have three
different cases of the deficiency indices: (i) n+= n. = 0, (ii) n+= n. 0, and (iii)
n+* n.. Cases (i) and (iii) are simple, where either a densely defined operator is
or is not selfadjoint, but case (ii) is much more complicated. Discussions such as
how to add boundary conditions on the wave functions in order to extend the
Hamiltonians to be selfadjoint, and what kind of physical interpretation those
extensions imply, etc., will be presented in Â§3.2 and Â§3.3.
3.1 Three Different Cases of Hermitian Hamiltonians
In this section we will apply Theorem si & 2 to four general types of
Hamiltonian, just as we did in Â§1.2 for H = p2 + x3:
22
23
(1) H = p2bxm,
(2) H = p xm + xm p,
(3) H = p2 + p xm + xm p,
(4) H = p2 + xpm +pmx
where m is a positive integer and b is a real constant. Those four types of H cover
all the Hamiltonians discussed in chapter 2.
3.1.1 H = P2 bxm
Obviously, H is Hermitian. Similarly to what we did for H = p2 + x3 in
Â§1.2,let
H+ i/4= i i//
withp = id /Ax,
(Â£2 + bxm)v = + W.
As both b and m are real, i//: = \p+ Thus, n+ = n. = n. So consider yr+ only; we
write
The asymptotic behavior of this equation as x > is given by
y/" + bx mt// = 0
since we require y/ (<) = 0. The solutions are given by Bessel functions:
24
yKx) ~ VJxf Zi/(m + 2)( 2 ^ Vxm+2)
m + Z
where Zv ~ /v, Nv, /v, or Xv, which are Bessel functions of the first and second
kinds, respectively. To examine whether or not \ I yKx) 12dx converges at x ,
we need to use the following asymptotic forms of the Bessel functions:
i y I  + ~,
y(v+i>
2 2J
Nv(y)~
fv(y)~p=exp(y)
V2/ry
Kv(y) ~Vfexp(y)
If J I y/Or) 12dx converges, then iy(x) e D(H+) c ^.
Examples:
(a) H = p2 + x4 :
y/' x4y/= iyj
near Ixl ~ <, y/ 0; thus,
y/' x4iy= 0.
25
Then b = 1 and m = 4. We should choose Z ~ IV/ Kv (with y = 1/3 I x 13), the
Bessel functions of the second kind.
For x ~ oo, y/(x) ~ VJxfJCi/lW3)/ so n+/ ^ = 1
n+ = n+/ +00 + n+r., 2 = 1 + 1 2 = 0 = n., i.e., (n+/ n.) = (0,0).
Thus, H is selfadjoint in <*>, + )), which makes possible the global solution
of the Schrodinger evolution equation (see Sections 9.6 and 9.7 of Ref. 3); the
existence of the bound states y/+ and iy: implies a discrete spectrum of energy.
(b) H = p2x4 :
y/' + xAy/= iy/
Here b = +1 and m = 4; thus
V^2)(x)~VxJi/6*3) and VxNi/6(ix3) ~ (l/x)cos or sin (ix3 }k).
wl J J J
It is easy to check that both of the solutions are in so n+ +co = 2 = n+>. ^ as yris
symmetric on x.
n+ = 2 + 22 = 2 = n., i.e., (n+, n.) = (2,2).
Two boundary conditions are required to extend H to be selfadjoint, and a
discrete energy spectrum is expected.
Indeed, even a WKB analysis leads to a discrete spectrum.
Jv will make the integral diverge, and therefore is not allowed.
26
(c) H = p2 x2 (p2 + x2 is similar to p2 + x4 )
\\i' + x2y/= iyt
where b = 1 and m = 2.
2>W ~ YRM}*2) and VJxfN1/4(i*2) ~ [xf 1/2cos or sin {\xA 2tt)
T 4 4 4 8
but neither of them are in L2(Q); therefore,
(n+, n.) = (0, 0)
and H is selfadjoint, but its spectrum is continuous because no bound states
exist. Again, this conclusion follows from WKB arguments as well.
(d) H =p2 + x (p2 x is basically the same )
v4 ^ v'+ = *>+
VÂ£ (x i)V4 = o.
For x > 0, b = 1 and m = 1,
V4(x) ~ 1xiKV3(kx if'2),
O
which is in Â£2.
27
But for x < 0, b = + 1, and m = 1,
V?' 2)W ~ VjxJ + i /i/3(
where we have ignored the unimportant phase term. Both of the solutions are
not in Â£2 (the square integral of y/+ diverges at x ~ ). That means there is no
solution for x < 0, and no solution could be connected to yr+, x >0 either.
Therefore, we have
(i) (n+r n.) = (0,0) for Q = (, 0),
(ii) (n+, n.) = (0,0) for Q = ( <*>, + <),
(iii) (n+, n.) = (1,1) for Q = [ 0, + 00).
The spectrum is expected to be continuous in (i) and (ii), but discrete in (iii).
This is an interesting system. In section 3.2, we apply it to a particle in a
gravitational field and a uniform electrical field.
3.1.2 H = pxm + x mp
By substituting p ~ i d/dx and using [p,rm]=irnrm'1,we get
(p xm + x m p )!//+= (2p xm imx mA )y/= i y/
/
2xmy/ = (+1 mxm A)y/
(i) m = 1, 2x\p = (+1 l)y/f
2xy+= 2\Â¡/+,
xy/.0
28
with V4 ~ 1 lx., which is not in Â£2 since it diverges too rapidly at x ~ 0, and y/. =
const., which is not in Â£2 either. Therefore,
(n+, n.) = (0,0)
Thus, H = px + xp is selfadjoint and its spectrum is continuous.
(ii) m > 1,
2y/ /ip = (+1 mxmA)lxr
V ~ x w/2exp ( 1 xl'm)
2(ml)
As x ~ 0, y/ ~ which are square integrable, so 00 are regular points.
But now x = 0 is a singular point. Checking y/ near x = 0, we find
m = odd, n. = 1, n+ = 0, which has no selfadjoint extension. H is not self
adjoint and has no complete evolution, just as was the case for H = p x3 + x3 p in
Chapter 2.
m = even, n. = n+ = 0, H is selfadjoint with continuous spectrum. See the
example of H = p x2 + x2 p in the previous chapter.
It is interesting to point out that for 2 = ( 00, 0), (+, n.) = (0,1) if m = odd
and (1, 0) if m = even; for 2 = ( 0, + ), (n+f n.) = (0,1) if m = odd and (0,1) if m =
even. Therefore, H is not selfadjoint in both Q = ( >, 0) and Q. = ( 0, + ), no
matter whether m is even or odd. To explain that by the classical picture (see
example c in the table), we say that neither of those intervals could contain a
complete temporal evolution.
29
3 ] 3 H = p2 + p + x M p
In the above section, we found that p xm + xm p is not selfadjoint if m =
odd. Here we will show that by adding p2 to it, the situation will be changed
dramatically. First let us examine the classical solutions:*
H = p2 + p cjm +cÂ¡mp = p2+2pcjrn
Cj=2p + 2qm = 2 ^E + cj^m
(i) If m = 1, the solution is like that for H = p2 cÂ¡2, where H is selfadjoint.
(ii) If m > 1, the solution is similar to that for H = p2 q4, where boundary
conditions must be added to make H selfadjoint.
Second, let us see that quantum features of H:
H = p2 + pxm + x m p = p 2 + 2pxm imx m A
[p 2+ 2p x m imx m A)y/ = i y/
y + 2i xmy/+ imx mAy/ = + iy/
The asymptotic for near x ~ ~ is
// t
y/ + 2i x my/+ imx m A y/ = 0.
H =p2+ 2p qm, 2p = 2qm 2 VÂ£ + q2m 2p + 2pm= 2 Ve +
30
We introduce an equation with the solution given by the Bessel functions, i.e.,
O +[(1 2a)/x + 2ipyxY'l]0 + [(a2 v2?2)/*2? i/3)(y 2a)x r2] 0= 0
0 = xaexp (ipx y) Zvifay).
Note that \p just fits this equation by choosing
a =1/2, y=m + 1, P = 1/y, v=l/2(m + l),
i/oc ~ Vjjjexp ( i1xm + 1) Zv (1xm + 1) ~ 1/Vlxf
m + 1 m + 1
which is square integrable when m> 1*. So n+ co = n. 00 = 2, and
(+, n.) = (2,2), when m > 1.
So by adding p2, H always has selfadjoint extensions no matter whether m is
even or odd. This is exactly consistent with what we have just discussed from
the classical point of view.
As for the case m = 1, y/ ~ 1/Vpc[, which is not square integrable, so
(n+, n.) = (0, 0), which again agrees with what follows from the classical point of
view.
3 \ 4 H = p 2 + x pwi + p 171 x
Classical method:
* Here Zv /n, Nv.
31
p = dH/dcj = 2 pm
which is similar to cÂ¡ = 2 q m based on H = 2 p qm; therefore,
when m = even, H is selfadjoint;
when m = odd, H is not selfadjoint.
Quantum method:
x  id/dp, [x, pm] = imp m 1
(p2 + xpm +pmx )yf(p) = i y/(p)
/
2ip my/ = (i p2 imp ml)y/
y/~ (l/Vipp") exp + 2(^_ p1 m) x exp  i 2{Â£^ P 3'm) (31)
For m > 1: (n+, .) = (0, 0), if m = even,
(n+, n.) = (1, 0), if m = odd.
For m = 1, (n+, n.) = (0, 0) which has already been discussed in Section 3.1.3. We
see again that the classical picture is consistent with the operator analysis.
It is heuristic to observe that the last factor in Eq. (3.1) comes from the part
p1 in H, and it only induces a phase in the solution, therefore it would not change
the convergence or divergence of the square integral, i. e., the selfadjointness of
p 2 + x pm + pmx is exactly the same as x pm + pmx, and the latter one turns out
to be the same as p x m + xmp.
In other words, unlike the p2 in p2 + p xm + xmp, the p2 in
pl + xpw + p m x will not change the properties of selfadjointness.
32
3.2 The Application of Boundary Conditions and SelfAdjoint Extensions at
Regular Points
Examples:
(a) A p = 1 d/dx, with Q. = [b, a]
p y/=+ iy i/4 = exp (+ x).
Thus, n+ = n. = 1, apply theorem 3 to this case, we have
/ri=ciV4+c2ye, Ci,C2& C
0 = (/i,/i> = < / d/,/dx, /,) (/,, dfr/d*) 1 [It
= i[/i(/i'(W/iW/i(a)].
Set fi(b)/fi(a) = z ; we have 2 z* = 1, so z = exp(iO), ^ For selfadjoint D(M) =
[y/(x): (yr, /i) = 0],i.e.,
m /Â¡(b) yKa) f{(a) = 0
t/AW/i//(a) = exp (iff) (3.2)
let us look at the eigenfunctions of p :
m = A 1/4,
V4 ~ exp (Ax)
33
V'#)/ \Â¡fx{a) = exp (i'A( b a))
y/x has to satisfy (3.2) to be in D(M); so we get
A(ba) = 6+2m n = 0, 1, 2,...
A = (d+2m )/(ba).
The case of 6 = 0 is what is usually considered in quantum mechanics, and is
called the periodic boundary condition.
(b) H = p2 + x, with 2 = [0, + oo)
As we already discussed in (d) of Section 3.1.1, n+ = n. = 1 for Q = [0, + oo).
Therefore*
0 = (Ml) = (p2/i + M/i) (/i, p 2/i + xfo = (v2h>/i) (h,p2h)
= (/i A /i fl) 10+~=A(o)/i(0) /i(0)/>).
So
fi(0)//1(0)=[/1(0)//1(0)J = tan6>
0 91,
D(M) = [!//(*): ( v^,/i) = 0 ], so the boundary condition at x = 0 is
i//(O)cos0 y/(O)sin0 = 0
(3.3)
34
In fact, at any regular point, the form is the same.
Consider a particle with 1/2 unit mass moving vertically in the earth's
gravitational field and set x = 0 at the surface of the earth, Q = [0, + ). Then its
Hamiltonian is given by
H = p2 + mgx = p2 + x, by setting g = 2.
It is interesting to note that this system has a natural selfadjoint extension
set by y(0) = 0. That is the case of q = 0 in the above boundary condition (3.3).
Additionally consider a physical system of an electron in a uniform
electric field E applied in the + x direction. The form of the Hamiltonian is then
H = p2 + x with Â£2 = ( o, + o). For such a system, no special boundary
condition is needed since n+ = n. = 0.
3.3 The Application of Boundary Conditions and SelfAdjoint Extensions at
Singular Points
In this section, we will look at the effect of an attractive central potential.
We discussed in the classical point of view that there is no trouble for systems
with nonrelativistic Coulomb potentials, since they have a full time evolution.
Here we will see that this holds because they are selfadjoint. We will also find
selfadjoint extensions for the superattractive potentials [V(r) = A/r", n > 2].
After separating the angular part from the radial part, we have
Hr = d 2/dr2 + 1(1 + l)/r 2 + V(r)
which acts on u(r) with the requirement that w(r)p dr must converge.
35
(i) V(r) = A/r, A > O
Hr+ u = i u, u + (i + A/r 1(1 + 1 )/r 2)w = O
becomes, at small r,
u + (A/r / (/ + l)/r2)u = 0
u ~ VT Z (2/ + d(2Ar) ~ VT (iflrf(2 +1}.
Thus, with / > 0, n, 0+ = 1
//
At large r, w iu = 0
and its is not hard to find that
"+/ + ~ = 1
Therefore, (n+f n.) = (0,0) for H with a Coulomb potential.
(ii) V(r) = A/r2
u + (i +A/r 2 / (/ + l)/r2)u = 0.
At small r, the eigenfunction ue and u have the same form:
36
//
A / (/ + 1)
+ T
= 0
u,uE~rP, p = 1/2 V 1/4 (A / (/ + 1))
For an swave (/ = 0) with A > 1/4 or A /(/ t1) > 1 /4, we have
u, ~ r 1/2sin (A'ln r), or r^^osiA'ln r)
where A' = [A / (/ + 1) 1/4]1/2. Then n 0* = 2. With n+00 = 1, we get
(n+, n.) = (1,1).
Now let us construct selfadjoint extensions: at small r,
fi = ci r1/2cos(A'ln r) + C2r 1/2sin(A'ln r).
Using ( o* [0 V* and noting that ( ) is a bilinear form on
D(H+)xD(H+), and(g h ) = (h,g j, we have
Thus,
(r1/2sin(A'ln r),r 1/2sin(A'ln r) )o* = 0
(r 1/2C0S(A'ln r),r 1/2COs(A'ln r))jr = 0
(r1/2cos(A'ln r ), r 1/2sin(A'ln r ) )b+ = A'
o = (/i,/i) = (ciC2 cic2*)A cic2= real.
Consequently c2/ci is also real. Set c2/ci = tan 8, where 6 e 9; then
37
fi ~ r1/2cos(A'ln r 6)
The eigenfunctions have the same form at small r, i. e.,
ue = Cev1/2cos(A'ln r 6)
in order to satisfy (Â£,/i ) = 0. In Ref. 4, the author found the dependence of
eigenenergy on the choice of 6. Because of 6, we have a oneparameter family of
selfadjoint extensions.
Further, D(M) = [ u(r): ( u, /i) = 0 ], and therefore the boundary condition
at r = 0 is given by
lim
rCT
u '(r)r1/2cos(A'ln r 6)
u(r) (r1/2cos(A'ln r 6))
dr
= 0
(hi) V{r) = A/r", n >2,
at small r,
uP +(Â£ +A/r" /(/ + l)/r2)wE = 0.
Ur +(A/rn)uE = 0
uE ~ VfZi/(+i)=&r(2)/2
Ln2
Using the Bessel asymptotic forms, we get
ue ~ r"/4sin(yr('2)/2)
or
38
rn/4 cos(yr(2)/2)
where y= 2X /( 2). u have the same form, so nÂ¡ 0* = 2, (+, n.) = (1,1).
The boundary condition is similar to (ii)
h ci r"/4 sin(yr (n _2)/2 ) + C2r/4 cos(yr'2)/2)
using
(r/4 sin(yr _2)/2 ), r"/4 cos(y r(n 2>/2 )b = A1/2
Thus,
(/i//i)=0 gives C2/ci=tan6, 0e SR
fi ~ r"/4 sin(yr(_2)/2 + 0)
we = Ce r"/4 sin(yr
D(M) = [ w(r): (w, /1) = 0 ],
gives the requirement on u(r) at r > 0
lim
r > 0*
u (r)r n/4 sin(yr 2)/2 + 6)) u(r) (r/4 sin(yr
t/r
= 0
3.4. Conclusion
By calculating the deficiency indices for several representative examples of
Hermitian Hamiltonians, we have analyzed the possibilities in each case of
extending the operator to a selfadjoint one. In so doing we have confirmed the
39
connection proposed in the previous chapter that relates possible extensions to
associated characteristics in the solutions of the classical equations of motion.
The purpose of this chapter has been twofold: on the one hand, by demonstrating
that anomalies in the classical solutions to a dynamical system are reflected in
anomalies of the quantum Hamiltonian, certain technical issues ( such as
deficiency indices, etc.) are brought into the realm of everyday experience. On
the other hand, the intimate connection between classical and quantum
properties should enable one to examine a given system at a classical level in
order to assess what problems, if any, are expected to arise at the quantum level.
40
Table I Summary of classical and quantum highlights associated with several model problems Each model has a label, a classical Hamiltonian, typical
solution trajectories, nature of those solutions, character of quantum Hamiltonian, spectral properties, and. In some cases, related esamples as well T he
solid curve in the figure portion represents a typical trajectory or part of a trajectory in the case of a periodic orbit The dolled curve denotes an
alternative typical trajectory, and the dashed curve denotes a periodic extension o the basic orbit In d, the figure illustrates two possibly distinct periodic
extensions, h is omitted because it is a related example of d.
Example
Label
Classical
Hamiltonian
H
Qualitative Graph
t(q) of equations
of motion
Nature of
Classical
solutions
Selfadjoint
Quantum
Hamiltonian
Spectral
Properties
Related Examples
m = 1,2,3,
a
p + 4
t
m
global
unique
discrete
p + i,m
t
p + 3
t
periodic
one parameter
family of
solution (one
boundary
condition)
discrete
p5?5
p ?,m+>
c
2p?5
t
.
r
partially
complex
nonexistent
none
pqm m > 1 m = odd
d
P5 1*
t
'
W
periodic
two parameter
family of
solution (two
boundary
conditions)
discrete
p m > 2
p5 + 2p7m m > 2
t
p
t
f
global
unique
continuous
PJ + 2p
41
1 able I (Continued )
Kxample
label
Classical
Hamiltonian
//
Qualitative Graph
(7) of equations
of motion
Nature of
Classical
solutions
Selfadjoint.
Quantum
Hamiltonian
Spec t ral
Properties
Related Pxarnpl's
mr 1.2 n
/
2p?7
global
unique
continuous
/ 7>m rn > 1 ?u even
9
2 v/l
A
t
t
/ ?
e*
part Â¡ally
complex
nonexistent
none
2;i/7n m = odd
\
2 r/i + p
^
\
piece wise
continuous
one parameter
family of
solution
continuous
P7 + 2 p/
j
P? + ^
A > 0
Â£
1
AA,
i
<' '
i i
global
unique
discrete
t
yi2 A 4 !liU
/ r r" r *
A
A.
>
x*
x tr
periodic
one parameter
family of
solution.
discrete
42
Table I. (Continued.)
Example
Label
Classical
Hamiltonian
H
Qualitative Graph
t(q) of equations
of motion
Nature of
Classical
solutions
Selfadjoint
Quantum
Hamiltonian
Spectral
Properties
Related Examples
m = 1,2,3,
/
2 PI
i
\
\
r'
global
unique
continuous
m
P5 + V
:
global
unique
continuous
Fig. 1 Classical trajectories for the simple Hamiltonian H=p in three separate coordinate domains: (a) oc
(b) 0
PART II
OPERATOR ANALYSIS
AND
FUNCTIONAL INTEGRAL REPRESENTATION
OF
NONRENORMALIZABLE MULTICOMPONENT ULTRALOCAL MODELS
CHAPTER 4
INTRODUCTION
As we know, the features of infinitely many degrees of freedom and
noncompact invariance groups have made the structure of quantum field
theory very complex. So seeking for the proper formulation of problems in
quantum field theory has been a difficult yet exciting endeavor in our
research. Even though conventional perturbation theory5'6, which is based on
a free field formulation, has proved successful in solving some problems, e.g.,
quantum electrodynamics (QED), we must ascertain whether the free field can
be generally used as the basis for a perturbation expansion7. One of the results
that arose from the traditional perturbation analysis based on free fields is the
appearance of nonrenormalizable interactions which some physicists regard
as hopeless. Therefore the structure of nonrenormalizable models has been
largely ignored over the years. Twenty years ago, the pseudofree theory was
proposed by Klauder7'8 in the study of ultralocal field models to extend the
usefulness of perturbation theory. An argument based on asymptotic
convergence suggests that the free theory is connected with continuous
perturbations while the pseudofree theory is related to discontinuous
perturbations, which have much to do with nonrenormalizable interactions.
At about the same time, a functional and operator approach to single
component ultralocal field models was developed through general
nonperturbative and cutoff free arguments9'10. There Klauder gave an
44
45
alternative quantum theory of such models, which does not fit into the
canonical framework. He also showed that as any interaction is turned off.
after it was once introduced, the theory will not pass continuously to the free
theory, but rather to a distinctly different pseudofree theory. Clearly,
conventional perturbation theory could not be applied to such a model.
The ultralocal model is obtained from covariant model by dropping the
spacegradient term. Since distinct spatial points there characterize
independent fields for all times, it unavoidably results in a
nonrenormalizable situation. We are interested in this model because it is
solvable by nonperturbative techniques and may give us some insight into
the structure of nonrenormalizable fields.
In chapter 5, we will show that just like nonrenormalizable relativistic
quantum field theories, on one hand they exhibit an infinite number of
distinct divergences when treated perturbatively, while on the other hand
they frequently reduce to (generalized) free fields when defined as the
continuum limit of conventional latticespace formulation11, ultralocal
models are specialized nonrenormalizable theories that also exhibit infinitely
many perturbative divergences and an analogous (generalized) freefield
behavior when defined through a conventional lattice limit12. However, the
characterization of infinitely divisible distributions13 allows ultralocal models
alternative operator solutions9'10 (also Chapter 6), which lead to a nontrivial
(nonGaussian) solution on the basis of operator methods. The validity of
this nontrivial solution is supported by the fact that the nontrivial quantum
solution reduces to the correct classical theory in a suitable limit as h > 0; the
trivial (Gaussian) solution has no such correct classical limit (Chapter 7)12.
Recently, it has been found how to obtain the same nontrivial results
offered by operator techniques through the continuum limit of a
46
nonconventional latticespace formulation14. The key ingredient in the
latticespace formulation that leads to the correct behavior is the presence of
an additional nonclasssical, local potential besides the normally expected
terms.
In chapter 6, we will construct the operator theory of 0(N)invariant
multicomponent nonrenormalizable ultralocal models, where N < <*>. It has
been surprisingly found that the singular, nonclassical term in the
Hamiltonian which showed up in the onecomponent ultralocal fields can be
made to disappear15, when N, the number of field components, satisfies N>4.
Nevertheless, a similar singular, nonclassical term still appears in the
regularized pathintegral formulation16 that leads to the same nontrivial
quantum results for O(N) invariant multicomponent scalar fields (Chapter
8). Thus, for any N, the number of field components, the new path integral
formulation involving the singular, nonclassical term replaces the standard
lattice approach which invariably leads to a Gaussian theory regardless of any
nonlinear interactions, and supports the concept of a pseudofree theory.
One advantage of deriving the operator solutions by a latticespace
formulation is the clear focus the latter approach places on the differences
from traditional approaches needed to lead to nontriviality. These differences
for ultralocal models suggest plausible modifications in the latticespace
formulation of relativistic nonrenormalizable modes that may lead to
nontriviality for Ncomponent models such as n > 5 (and possibly n = 4),
for N > 1.
In my future research, I hope to extend analogous reformulations to
covariant quantum fields, the possible relevance of which has already been
noted23. The general argument is partially based on the realization that the
47
classical theory of a typical nonrenormalizable interaction exists and is
nontrivial24.
CHAPTER 5
CLASSICAL ULTRALOCAL MODEL AND THE STANDARD
LATTICE APPROACH
The classical Hamiltonian of an ultralocal scalar field is expressed as
Hci = j Ji7C2(x) + lm2(p2(x) + Vi[(p(x)] jdx (5.1)
where n, cp denote the classical momentum and field respectively, and Vi[cp]
(= Vi[ 
configuration space of arbitrary dimension, xe9?n l. This model evidently
differs from a conventional relativistic field theory by the absence of the term
The classical canonical equations of motion appropriate to (5.1)
become
iWx)]
(x,t) = & = 7i(x,t),
5rc(x,t)
ir(x,t) = 5Hcl = m2(p(x,t) Vj[(p(x,t)], (5.2)
5
Cp(x,t) = m2(p(x,t) Vj[cp(x,t)].
Unlike conventional canonical field quantization, the quantum theory
of ultralocal fields does not follow from standard canonical commutation
relations, etc., whenever a nonlinear interaction exists. In particular, we do
not have an equation such as (5.2) for local quantum operators (see Chap. 6).
48
49
Nevertheless, it is instructive to first examine these models from a
conventional lattice limit viewpoint.
Let us take a look at the result from a standard functional integral
approach (which is based on the standard canonical quantization) where the
vacuumtovacuum transition amplitude is formally given by 6:
ZQ] = ^ exp; i
cf x J(x,t)(x,t) + Li (x,t) L (m^
2 2
ie) 02(x,t) g
r
4
where we have chosen VÂ¡ (O) = gO as an example. Using a latticespace
regularization in the space direction (but not in the time direction) we obtain
I
Z[J] = 9\i lim^o I (FI 2>k) exp i dt Ik a
I
Jk(t)4>k(t) + Lk (t) L (m2 ie) 4>Â£(t) gOÂ£f(t)
2 2 .
J,
= limfl^0 IT j exp> j dt a
I
J k(t)
2 2
where k labels points in the spatial lattice and a is the volume of the unit cell
in the spatial lattice. As we now show, the result for such an interacting
model leads in the continuum limit to the analog of a generalized free field.
From the preceding equation, using u = O Va, go =g/a, and < > as an average
in the complex distribution, we have
Z[J] = Vi lim^o n
k
J k(t)u(t)V +l2(t)
2
50
I
limado II < exp{i I dt J k(t)u(t)Va } >
= lim^oll {l [ I J k(t)u(t) dt ]2> + [ I J k(t)u(t) dt ]4 > + }
4!
/
= exp {1/2 I d x dt dt' J(x, t) J(x, t') < u(t) u(t') > }.
(5.3)
Evidently (5.3) is a Gaussian result in which (assuming 0
J,
< u(t) u(t') > = ti I 'Du u(t) u(t') exp ji dt
I
l2(t) 1 (m2 ie) u2(t) gu4(t)]
= < O IQ exp( i I tt' IH )Q I 0 >
= ^<0 I Q I n > e < n I Q I 0 >
y Pn q i I tt' I mn
n 2mn
(5.4)
where mn, n=l, 2, 3, denote the eigenvalues of H,
Pn = I < 0 I Q I n > I 2.
2mn
H = 1/2 (P2 + m2^ ) +gQ4 const., and the constant is chosen so that H10 >=0.
It is easy to verify that ^ pn = 1, and since < 01QH4Q 10 > < it follows that
n
oo
^ pnm^ < oo. Thus we have
zm=exp{l/4 j d3xdtdt'J(x,t)J(x,t)X (pn/mn) e *iltt'lmn }
51
= i! exp {
n
d3 x dt dt' J(x, t) J(x, t')eilM'lm" }.
(5.5)
The ultralocal free field corresponds to g= g=0, in which case mn = mn ,
Pi = 1/ Pn = 0 (n*l) in (5.4), so that
< u(t) u(t) > =_Leiltflm .
2m
Then (5.3) gives
Zf[J] = exp {
d3 x dt dt J(x, t) J(x, t1) e 11 t_t'1 m }
= <0 I Texpfil d4xJ(x,t)Op (x,t)} I 0 >. (5.6)
Observe that the ultralocal free field operator Op (x,t) satisfies
m m
Op (x,t) + m2Op (x,t) = 0.
Comparing (5.5) and Eq. (5.6), we get
Z\J] = n < 0 I Texp {i
d4x\^J(x,t)0n(x,t)} I 0 >
d\ J(x,t) X Vp^0^n(x,t)}
0>
= < 0 I Texp {i
= < O I Texp {i I d'Sc J(x,t) 0(x,t)} 0 >,
(5.7)
where (x,t) =X Vp^OF^fot). 0?ln(x,t) are ultralocal free field operators with
n
mass mn t n = 1,2,3 ,which satisfy Op "(x,t) + Opln(x/t) = 0 for each n.
From (5.7) we see that our regularized interacting model has led in the
continuum limit to an ultralocal generalized free field, a natural analog of the
relativistic generalized free field17. As a consequence of
[0(x,t), [0(y,t), 0(z,t)] ] = 0, which holds for a generalized free field under our
present conditions, it is clear that the field operator C> of an interaction like
4
Vi (O) = g with g>0 can not satisfy this commutation equation. Obviously
this (generalized) freefield behavior is limited neither to g
replaced by other local powers), or to the spacetime dimension n=4. This fact
indicates some sort of failure of the conventional formulation of canonical
field quantization for these models. Moreover, with the help of coherent state
techniques18'19 we find that the classical limit of an ultralocal generalized free
field does not limit as (h 0) to a classical field that satisfies the classical
nonlinear canonical Eq.(1.2); instead, the classical limit of
n n
CHAPTER 6
OPERATOR ANALYSIS OF MULTICOMPONENT
ULTRALOCAL MODELS
The quantum theory of ultralocal scalar fields had been discussed
extensively by Klauder9'10 over two decades ago. The employment of probability
theory and Hilbert space methods with an emphasis on infinitely divisible
distributions and coherent states techniques, respectively, enables us to give a
proper quantization of these models, which otherwise are meaningless within
the conventional canonical formulation of quantum field theory (see chap. 5).
An operator solution of multicomponent, nonrenormalizable,
ultralocal quantum field models is developed here along lines presented
earlier for singlecomponent models. In Â§6.2, we will show that the
additional, nonclassical, repulsive potential that is always present in the
solution of the singlecomponent case becomes indefinite and may even
vanish in the multicomponent case. The disappearance of that nonclassical
and singular potential does not mean a return to standard field theory. The
operator solution of multicomponent ultralocal fields remains
noncanonical. In Â§6.3, we will show that nontrivial, i.e., nongaussian, results
hold for any number N of components, and suitable nontrivial behavior
persists even in the infinitecomponent ( N= ) case as well.
53
54
6.1 Operator Analysis of SingleComponent Ultralocal Models
Let us briefly summarize the operator analysis of singlecomponent
ultralocal models9'10. Assume that the field operator O(x) becomes self
adjoint after smearing with a real test function f(x) at sharp time. Since
distinct spatial points characterize independent fields for all time, we may
write the expectation functional as
(6.1)
Where in the last step, we have used the result of Levy's canonical
representation theorem for the infinitely divisible characteristic functions13,
and have eliminated a possible contribution of the Gaussian component,
which applies to the free field. The real, even function c(A) is called the
"model function".
An operator realization for the field O(x) is straightforward. Let
A+(x, X) and A(x, X) denote conventional, irreducible Fock representation
operators for which 10 > is the unique vacuum, A(x, A,) 10 > = 0, for all
xe 9ln \ Xe 9L The only nonvanishing commutator is given by
(6.2)
Introduce the translated Fock operators
55
B(x,X) = A(x, X) + c(X), B+(x,W =A+(x,W + c(X), (6.3)
Obviously, the operators B+(x, X) and B(x, A.) follow the same commutation
relation (6.2). Then the operator realization for the field O(x) is given by
The correctness of this expression relies on the fact that
I
< 0 I exp{ i I dxO(x)f(x)} I 0 >
=< 0 I exp {i
=< 0 I: exp {
i j dxj dA. B+(x,
j dxj dX. B+(x,
X) Xf(x)B(x, X)} I 0 >
?0(eW*>l)B(x,X)}:l 0>
= exp { j dxj dX [ 1 e^M] c2(X.)}
as required by (6.1).
The Hamiltonian operator is constructed from the creation and
annihilation operators and is given by
H = J dxj dX. B+(x, X) h(d/dX, X) B(x, A,)
56
= j dxj dX A+(x,
X) h(B/3X, X) A(x, X).
(6.5)
Where h(3/3X, X) = b2d2/dX2+ V(X), which is a selfadjoint operator in the X
variable alone. It is necessary that h(3/3X, X) > 0 in order that H > 0 and that
I 0 > be a unique ground state. Equality of the two expressions in (6.5) requires
h(3/3X, X) c(X) = 0, implying that c(X) e L2 in order for 10 > to be unique. This
relation also determines V(X) as V(X) = b2 c"(K)/c(k). Assuming that
dXX2 c2(X) < o, so that <0 I02(f) I0>
I
I
I
together with the condition I dX c2(X) = we are led to choose
c(W=l^exp{^mx2y(4
(6.6)
where y, called the "singularity parameter", satisfies l/2
have (pk = ih B/BX )
h(B/BX, X) = b2^ + Y(Y+1)^2 + m(Y. 1/2)h + Wx2 + Vi(X)
2 BX2 2X2 2
= }:Px2 +^^ + m(Yl/2)^ + iin2X2 + VI(X), (6.7)
2 2X 2
Vi(X) = y ( y" + y'2) + ( mftX + yh2/\ ) y'. (6.7b)
This equation determines c(X) for any given interaction potential VÂ¡(X), at
least in principle. Notice that in addition to the free term p^2 + ^m2X2 and
2 2
57
the interaction term Vi(A.), there appears a nonvanishing, positive, singular
and nonclassical potential y(y+l)h2/2X It is important to note that this
additional potential makes the pathintegral formulation of ultralocal fields
totally different than that of standard quantum field theory14.
The definition of renormalized local powers of the field follows from
the operator product expansion
O(x) O(y) = 5(xy) di B+(x, X) X2 B(x, X) + :
which suggests the definition
I
dX B+ (x, X) X2 B(x, AO = Z O2 (x), Z'1 = 5 (0) (6.8)
or more generally,
Ork(x) =J dX B+(x, X) Xk B(x, X) = ![Z 0(x)]k, k = 1,2,3, (6.9)
For k > 1, these expressions are local operators, i.e., become operators when
dA, B+(x, X) 1 B(x, A.), and
X
I dA. B+(x, X) B(x, X) = O,.1 (x), then we can extend (6.9) for renormalized
J X
k
negative powers of the field. But we should note that for k < 0, r(x) are not
local operators.
l,
smeared by a test function. For k < 0, let O (x) =
sZf
58
Corresponding to (6.7), the Hamiltonian may be expressed by
renormalized fields as
H = j (irx) + Im2
2 2 92 0
where nr = Or+ y(y+l)/r Or + m(2yl)h Or. Obviously it means that nr
neither fits into the canonical framework! flr = Or ) nor fulfills the standard
canonical commutation relation [Or(x), nr(y)] = i hb(x y). We should also
notice that although Or ( = O = i [ O, H ] /h = ifr J d\ B+(x, X) d/dX B(x, X) ) is
not a local operator due to the assumption regarding c(X), neither are
220 2
Or,Or ,0>r local operators by themselves alone; only the combination Fir is a
welldefined local operator. These are major differences from standard
quantum field theory.
The Heisenberg field operator is given by
0(x,t) = eiHt/;' ch(x) e'Ht/fi
I
I
dX B+(x, X) eiht/rXeiht/* B(x, X)
dX B+(x, X) ?.(t) B(x, X)
(6.11)
which is well defined. The timeordered truncated npoint vacuum
expectation values are given by
< 01T [0(Xl,ti) 0(x2,t2) T
59
= 5(xrx2) 5(x2x3)
5(xnixn)
 dX c(X)T [ X(ti) X(t2) X(tn)] c(X).
(6.12)
For ultralocal pseudofree fields ( defined when the interaction
potential Vi(X) vanishes ), we have the model function
c(X)=x'Y exp { mX2/2h }, and the expectation functional
E[f] = exp {
M
dX
1 tos [ Xf(x) ]
W*
exp
(6.13)
which is obviously not a Gaussian solution such as for ultralocal free fields.
In Â§6.2, the operator analysis of finitecomponent ultralocal models is
presented. There we will see how an indefinite (positive, negative or
vanishing), singular, and nonclassical potential affects the operator solutions.
In Â§6.3, the expectation functional of infinitecomponent ultralocal
fields is discussed. Even in this case the solution of any interacting theory
does not reduce to that of the free theory in the limit of vanishing nonlinear
interaction and again supports the concept of a pseudofree theory7'8.
60
6.2 Operator Analysis of FiniteComponent Ultralocal Fields
Following the pattern of the singlecomponent case, the field operator
and the Hamiltonian of N component ultralocal fields are defined by
0>(x) =
I
dX B+(x, X) X B(x, X)
(6.14)
and
dX B+(x, X) h(Vx, X) B(x, X)
dX A+(x, X) h(V^, X) A(x, X)
(6.15)
where h(Vx, X) = + V(A), X svr2. Notice that here the Ncomponent
ultralocal models under consideration have O(N) symmetry. The
commutation relation becomes
[a(x, X), A+(x', X')} = 5(xx') 6(XX')
(6.16)
and the unique ground state satisfies A(x, X) 10 > = 0. The operator B(x, X) is
related to A(x, X) by
B(x, A.) = A(x, X) + c(X).
(6.17)
The renormalized local powers of the field are given by
61
I
^ri,...ik(x) = dX BT(x, X) A*, ^ik B(x, X), ii, ,ik = 1, 2,3, N
Occasionally, we need to use the renormalized negative powers of the field
even though they are not local operators. Take a singlecomponent case for an
example:
Orf(x) =
I
dXB+(x,M,kB(x,?0 = L[Z Oi(x)]1
2]
i = 1,2 N,
(6.18)
which can be extended to k < 0, as long as we define
Oj1 (x) =Z21 dXB+(x,X)JB(x,X) and dAB+(x,X)JB(x,)t) = 4>ri(x).
1 h J h
From the requirement that h(V^, X) c(A.) = 0, we have
1 ? 2
V(A,) =Hi Vxc(X)/c(X). The real, even model function c(X) becomes
c(X) = exp  Yjrm^2 y(W
(6.19)
with N/2 < T < N/2 +
dNA. c2(X) = oo and
I
I
1 which is determined by the conditions
dNX X2 cKX) < oo.
Next let us find out how the operator h(V^, X) appears. From (6.19), it
follows that
V(X) = 1^2VX.c(A.)
2 c(X)
_ T? V d2
2 c(X) i=i a^2
C(X)
(6.20)
= r(r+2 ~N) + mh(T N/2) + m2X2 + Vi(X),
2X2 2
where Vi(X) = 1/z2 ( y" + y'2 ) + y' { mhX + [ T (Nl)/2 ] h2/X }, which
corresponds to the interaction. Therefore
h(VÂ¡, X) = ^2V + V(X)
2
= h2vl + F(F+2 N)h +mh(r N/2) + \m2X2 + Vi(X). (6.21)
2 IX2 2
This base Hamiltonian of multicomponent ultralocal fields is similar to that
of singlecomponent ultralocal fields (6.7); but a surprising difference between
the two equations is that unlike the nonvanishing, positive, singular and
nonclassical potential yiy+\)h2 / 2X2 appearing in (6.7), T(r+2 N)#2/2X2 is not
always positive and moreover it may vanish. These properties follow since
N/2 < T < N/2 + 1, i.e., 0 < T N/2 < 1 and therefore
2 N/2 < T+2 N = 2 + ( T N/2) N/2 < 3 N/2.
Summarizing, T+2N>0 for N<4; r+2N<0 for N>6; and T+2N is
indefinite, when 4
even equal to zero. As examples of vanishing T(r+2 N)/r/2X we have N=4
and T=2, or N=5 and T=3.
It is worth mentioning that the disappearance of T(r+2 N)ft2/2X2 does
not mean a return to standard (canonical) field theory or standard path
63
integral formulation; even in this case it can be shown that a similar non
vanishing, singular, nonclassical potential arises in the regularized path
integral formulation (Chapter 8).
It is worthwhile to discuss further the Hamiltonian which according to
(6.21), is given by
H =
= j inr(x) + im2Or(x) + Vi[Or(x)] dx.
(6.22)
2 2 0
Here nr(x) = Or(x) + r(r+2 N)/Â¡21 Or(x) I + m/i(2rN) lOr(x)l Notice that
j dX B+(x, X) (2 d2/dX,2 )B(x, X) ,
i=l, 2, N, are not local operators,
o 2
neither are On(x), IOr(x)l or IOr(x)l but somewhat surprisingly
N 2 =*2
^ On (x) = Or(x) is a welldefined operator for N=4 and T=2 and
i=l
N 2 0 ^*2 0
2_, On (x) + mÂ£ IOr I =Or(x) + m/z I
i=l
*2 =*2
and T=2, we have nr(x) = Or(x), which in the present case is a local operator,
but nr(x) = Or(x) involves local forms rather than local operators due to the ill
defined On(x).
Summarizing, the canonical equation nr(x) = Or(x) and the standard
canonical commutation relation [On(x), ft^fy)] = i^5jj5(x y) do not hold for
the multicomponent ultralocal fields, just as for the singlecomponent
ultralocal fields, irrespect of whether the singular potential T(T+2 N)2/2X
2
[~ I Or(x) I ] is present or not.
Analogous to the singlecomponent case, the Heisenberg field operator
is given by
64
/
dX B+(x, X) eiht/^Xe_iht/fi B(x, X)
dX B+(x, X) X(t) B(x, X)
(6.23)
which is well defined. It follows that the timeordered, truncated npoint
function reads
< 0 IT [(Di/x^ti) i2(X2,t2) ^(XnA)] 10 >T
= 5(xrx2) 5(x2x3) 5(xn.rxn) dX c(X) TlXJt!) Xj2(t2) Xin(tn>] c(X).
(6.24)
65
6.3 Operator Analysis of InfiniteComponent Ultralocal Fields
The expectation functional of finitecomponent fields is
E[f] = < 0 I exp
dx 3>(x)f(x) I 0 >
= exp { g
dX [ 1 e^'f(x)] C2(X)}.
(6.25)
Here we have introduced g a scale factor which cannot be determined on
general grounds but rather represents the only arbitrary renormalization scale
involved in the operator construction. The possibility of its existence lies in
the fact that two model functions differing by a constant factor lead to the
same differential operator h and thus to the same Hamiltonian H.
An operator realization of the infinitecomponent field requires us to
give a proper measure which is well defined. In doing so, notice that we can
absorb the model function c(X) into the measure so that we have the new
measure dp(X) = g c2(X) FIdXÂ¡. Let us redefine the commutator
A(x, X), A+(x', X')\ = 5(xx') 5P(X; X'),
(6.26)
where 8p(X; X') is related to the measure p by J dp(X) f(X)5p(X; X') = f(X). The
operator B and the infinitecomponent field are redefined as
66
B(x, X) = A(x, X) + 1,
(6.27)
O(x) = j dp(X) B+(x, X) X B(x, X).
(6.28)
Then we immediately recognize that (6.25) stays the same. The renormalized
local powers of the field and the Hamiltonian are given analogously by
ik(x) s j dp(A.) B+(x, X) Xu X[k B(x, X), h, ,ik = 1, 2,3,
N, (6.29)
and
H = Jdxj dp(X) B+(x, X) h(Vh X) B(x, X)
= j dxj dp(X) A+(x, X) h(Vx., X) A(x, X),
(6.30)
with the requirement of h(V^, A.)l = 0. The Heisenberg field operator is
given by
0(x,t) = eiHt/ft O(x)
j dp(X) B+(x, X) eiht/^eiht/a B(x, X)
l dp(X) B+(x, X) X(t) B(x, X).
(6.31)
The timeordered, truncated npoint function reads
67
< 0 I T [Oi,(Xi,ti) i2(X2,t2) Ojjx^tn)] I 0 >T
= 6(xiX2) 5(x2x3) 8(xn_rXn)
I
dp(X) TtXi/t!) XfeOa)  Xi.itn)]!.
(6.32)
It is worth mentioning that the above formulation for the infinite
component case is suitable for the finite component case as well.
Next we try to obtain the characteristic functional of infinite
component fields as the limit of finitecomponent ones. Take the general
form of c(X) = X Fexp  ^mA.2 y(A.)J in the finite case, then we have
E[f] = expj gj dxj dX [ 1 1 exp [ lmA.2 2y(X) ] (6.33)
In order for this limit to exist as we need to scale several parameters,
namely y=yN/ m=m>j and to choose a suitable factor g=gN Following the
Ref. 22, suppressing the integration over x, let us consider
68
where  dr rn ev = SL has been used. If we introduce the Fourier transform
yi+l
pair: e' 2YN^) = j d^ 1\n(!;) e'^, h^) = ^~j dX ei%k f L[f] can be
expressed as
lim
N> <
j dr r11 j dX [ 1 e^'f ] exp  (^mN + r) ^.2 + jh^C^) dÂ£,
The integration over X now involves simply Gaussian integration
j dx e^2 +^x = (^)N/2 e?/4a  and leads to
lim
N
_SN_ f dr rri / e N/2 [ 1 e?/ 4(mN/^ + r Â£)] hN(^) dt
(r1)! J0 mN/fi + r Â£1
= lim
N.
J dr r^mN/r/i iÂ£/r + i)'N/2[ l e?/ 4(mN/ti + r iÂ£)] hN(Â£) dE,
(rD! A
where 1 < 0 = TlN/2 < 0. Now we are ready to make the choice of y^, m^
and gN Assume that gN= g^'N/2(Tl)!, m^= m/N and yxA) = y (X/) which
suggests that h^f^) = N h(NÂ£). Following a change of variables of we take
the limit by using lim^^^i i + HlZLli^L) 1 expJL(m//i iÂ£)J,
and we get
L[fj = g I dr re expj ^(m/h Â¡5)J [ 1 e?/ 4r] h(Â£) d^
Jo
69
= g I dr re expj'^ (m/ft) 2 y(J)j [ 1 e?/ 4r]
/o
= g doexp((m/fz) a 2y(a)} [ 1 e c?/2], (6.35)
Jo (2o)e+2 1 1
where 1 < 0 < 0, and in the last step, we have substituted o = l/(2r).
We can also try in the following way to obtain the characteristic
functional of infinitecomponent fields as the limit of finitecomponent
ones. Take the general form of c(X) = X'Fexp j ^mX2 y(X) in the finite
case, then we have
E[f] = exp {
W
dp(X) [ 1 e^'f(x)] }
= exp g
I dx I dX [ 1 e^'^x)] exp [ lmX22y(A.) ]/
] ] i2r h I
1
(6.36)
In order for this limit to exist as Nwe need to scale several parameters,
namely y=yN, m=m^ and to choose a suitable factor g=gN Suppressing the
integration over x, let us consider
I
L[f] = dpN(X) [ 1 e^'fW]
(6.37)
I
2r
= Wn^oo gN I dX. [ 1 e1^'f ] J exp j fmN>.2 2yN(>.)
70
= lim
N>oo Â§N
j dX~ ^ exp  imN^.2 2yN(X) jj d [ 1 e&f cos 0]. (6.38)
Where dQ= sinN'2 0 d0 df2'. By changing the variable 0 0/N + k/2 and
taking N large, we have cos 0 = sin (0/N) = 0/N and therefore
~ ~ 2 N2 ~ 2
sinN2 0= cosN2 (0/N) [ 1 1(0/N) ] exp[ {0/N) (N 2) ]. Hence we
may write
J dQ [ 1 e&f cos Q]=J d0 exp[ i02(N 2) ] [ 1 e~ iXf0]J dÂ£T
2k.
N2
j dn' { 1 exp[lf2X2/(N2)]}
= S{lexp[lf2X2/(N2)]}.
(6.39)
Where S denotes the spherical surface area in Ndimensions, N 1, namely
S =
2 n
N2
N/2j dir.
Substituting (6.39) into (6.38), we have
L[f] =/zmN_>00 gN J dX i exp j lmNX2 2yN(X) I S {1 exp[ lfV/(N 2)]}
J ^2rN + i \ J 2
= W*N>oogN j dXN y)/2SCxpjlmNNX2 2yN(f" X)j {1 exp[lf2X2^L]}.
In the last step we have made a change of variables of X>V~ X', p = 21" N + 1.
71
Now we must choose yu, mN and gjsj. Assume that mÂ¡sj= m/N,
yN(X) = y (X/V") and gN= N^'^/^g/S, where gis proportional to g in (6.35).
By taking the limit N<*>, we obtain
(6.40)
where 1< p< 3. So the characteristic functional of infinitecomponent fields
becomes
= exp g
From (6.41), we see that a nontrivial, i.e., nonGaussian, result holds for
infinitecomponent fields, just as it does for the finitecomponent ones.
Notice that the scalings we have used here, such as mw= m/N and
yrsA) = y (A./V), are different from the standard ones. For example: for
4 ~*4
Vi = O the standard scaling assumes (Vi)n = O /N, while the nonstandard
scaling employs mN= m/N and ytA) = y (A./V) which gives
(Vi)nIA.] = VitX/VbT] = X4/N2 or equivalently (Vi)n[0] = ViI/V] = 04/N2.
The nonstandard scaling admits a 1/N expansion relevant to the Poisson
distributed finiteN solution, while the standard scaling does not. Another
similar nonstandard scaling example was shown to hold in the independent
2 *2
value models where mfr = m2/N, (Vi)n[0 ] = VifO /N] are also used22.
72
Judging from these examples it would appear that the standard scaling may
fail for certain nonrenormalized fields.
CHAPTER 7
THE CLASSICAL LIMIT OF ULTRALOCAL MODELS
As given in chapter 5, the classical Hamiltonian of an ultralocal scalar
field may expressed as
Hci = j J~"7C2(x) + lm2cp2(x) + Vi[(p(x)]Jd3x, (7.1)
where xe SR0"1,7t,
the interaction potential. The classical canonical equations of motion
appropriate to (7.1) are
8rc(x,t)
7t(x,t) =  SHcl = m2cp(x,t) VÂ¡[cp(x,t)], (7.2)
5cp(x,t)
In fact, these formulas do not take into account a vestige of the quantum
theory that really is part of the classical action. Since the additional,
nonclassical, repulsive potential proportional to (field )'2 in (6.10) belongs in
73
74
the quantum Hamiltonian density, as 0 the coefficient of this term
vanishes save when tp(x) = 0. To account for this term we formally write
0(p'2(x,t) in the classical Hamiltonian density, and to respect this potential we
need to derive the equations of motion for (p(x,t) by means of a scale
transformation20, namely, using 8cp(x,t) = 5S(x,t)(p(x,t). This leads to a related
but alternative set of classical equations of motion (see Examples 1 and 2
below).
In the following, we will show that the alternative quantum theory of
ultralocal scalar fields described in Chapter 6 does indeed lead to the required
classical limit as h 0, thereby giving additional support to such an
alternative, nonGaussian solution.
7.1 Ultralocal Fields and Associated Coherent States
The proper quantum Hamiltonian of ultralocal fields given by (6.10)
has an evident connection with the classical Hamiltonian. In (6.10), the
subscript 'r' means the fields are renormalized, and instead of fl = O, we have
According to (6.4) and (6.5), the field operator O and Hamiltonian
operator are given by
B(x, X) = A(x, X) + c(X),
(7.3)
75
dX A+(x, X) h(, X) A(x, XX
dX
dX B+(x, X) h (, X) B(x, X), (7.4)
dX
with h(, X) = H2 + 7(7+l)h2 + im2>.2 + V^X)
^ 2 9X2 2X2 2
= \ Px2 + + ^X2 + V:(X), (7.5)
2 2r 2
( i_)
dX
Here we write the interaction potential as Vi(X) instead of Vi(X), since we
have used Vi as the classical interaction potential in (7.1). By using
exp(^Ht) B(x, X) exp( Ht) = exp[ it h(, X) ] B(x, X.) (7.6)
h h X
we can show that the Heisenberg field operator for any renormalized field
power is given by
OrG(x, t)= dX B+(x, X)exp[ M h(, X) ] X6exp[ t h(, X) ] B(x, X)
J dx ax
 dX B+(x, X) X6(t) B(x, X),
(7.7)
76
where XG(t) = exp[ 4 h(, X,) ] X6exp[ 4 h(, X) ] Even though
ft ax ft ax
[Or(x), nr(y)] ifi 8(x y), the variables X and p^ satisfy the standard one
dimensional canonical commutation relations. Therefore
X = L [X, h] = pi
in '
(7.8)
Pl4lR'hl= ,3
Y(Y+l)/r
m2X V^X).
We now introduce canonical coherent states for the ultralocal fields
I \/ > = U[y] I 0 >,
(7.9)
where, for each \/e L the unitary transformation operator
U[\j/] = expjj" dX d3x [\j/(x, X) A+(x, X) \j/*(x, X)A(x, X)]
(7.10)
It is straightforward to show that
U+[\/] A(x, X) U[\/j = A(x, X) + \jr(x, X),
U+ [\/] A+(x, X) U[f] = A+(x, X) + \]/(x, X);
(7.11)
evidently the same relations hold for B(x, X) and B+(x, X) as well.
77
7.2. Selection of the Coherent States for Ultralocal Fields and the Classical
Limit
Let us employ a Diraclike (first quantized) formulation for functions of
X, and in particular let us set
\}/(x, X) = (X I /f1/2 a(x)),
(7.12)
where
( X I K1/2 a(x)) = j^)1/4expj ^[x cp(x)]2 + i Xn(x) + i pj (7.13)
a(x) = L [ (p(x) + i 7t(x) ].
2
(7.14)
The expression (7.13) has the form of a conventional canonical coherent state,
i is an arbitrary phase, and I a(x)) = exp[a(x) a+ a(x) a] I 0 ) = U[a(x)] I 0 ), is
similar to the ordinary coherent state I a)18'19 except that in the present case
a is a function of x. a, a+ are the usual annihilation and creation operators,
which are related to X and p^by the relation
(7.15)
Note well the appearance of h in these various expressions.
In terms of these expressions we have
<\\i I Or(x) I \\f > = <0 I U+[\p] Or(x) U[\/] I 0 >
78
I
= I dA. < O I [B+(x, A,) + y(x, X)] X [B(x, X) + \/(x, A.)] I 0 >
= dX [c(A) + \/*(x, X)] X [c(A) + xt/(x, X)]
I
Since c(A) always takes the form c(A) =.^exp mA2 yi(A) it follows that
W 2n 1
f
lim^ _> o I dA c (A) A \y(x, A,) = 0. Consequently
lim^ _> o< VI $r(x) IV > = lim _> o I dA. \/*(x, A.) A, v/(x, X)
i j dX \/*(x,
1
= lim;, _>o I dA( K1/2 a(x) I X) A. ( X I K1/2 a(x))
= linv, _>o( 1/2 a(x) I A, I K1 /2 a(x))
= (p(x).
(7.16)
Before we calculate , we need to prove several useful
identities. By using
U^/f1/2 a(x)] X U[/f1/2 a(x)] = X + cp(x),
UV1/2 a(x)] pxU[r1/2 a(x)] = p^ + k(x),
we can calculate any arbitrary monomial in A's and p^ 's:
79
( h~1/2 oc(x) I ^01 p0n I K1/2 a(x))
= ( O I ( A, +
Because of the prefactor fh in the definition of X ( a + a+) ] and p^
[ = a+ a )], all the terms involving X and p^ will go to zero when we
take the limit > 0. Thus we have
lim/j o ( 1/2 a(x) I A01 p0n I K1/2 a(x)) = cp01(x> ^"(x). (7.17)
Now with h(, X) = h = h2^ + W{X) we calculate
dX
2 dX2
A(t) = exp(M: h) ^.exp( t h)
= X + it [h, X] + lM[h, [h, X]] + it)3[h, [h, [h, X]]]]
= X + tpi ijt2V (X) [v'(X) Pl + PiV'(X)] + .. (7.18)
After an expectation in the coherent states l/f1/2a(x)) and the limit 0,
we obtain
lim/j 4 o ( 1 /2 a(x) I A(t) I K1 /2 a(x))
=
(7.19)
80
where we have used (7.17), and introduced
Vo[cp(x, t)] = lim/j _> o V [cp(x, t)]. (7.20)
Notice that Vo(cp) no longer depends on h but it does contain a vestige of h
in the term 0(p'2(x,t).
We now prove that the result of (7.19) is just the solution
classical canonical equations with the Hamiltonian
d3>
i7T2(x,t) + V0[cp(x, t)] ,
k(x, t) = V0[cp(x, t)].
(7.21)
(7.22)
With (p(x, 0) = (p(x), 7t(x, 0) = 7i(x), we can use a Taylor series expansion:
cp(x, t) = (p(x, 0) +t cp(x, 0) t2 (p(x, 0) + 13 ^ +
2 3! at3
=
= (p(x) + t7i(x) v0[(p(x)] ^V0(cp(x,1)) I t = 0 +
= cp(x) +tJr(x)V0[(p(x)]V0[(p(x)]7i(x) + .... (7.23)
In the same way, we can prove that
81
lim/j _> o ( K172 tx(x) I p^(t) I Ti~1/2 a(x)) = n(x, t).
Thus
lim^_>0
= lim^ _> o< Â¥ IJ dX B+(x, A.) X(t) B(x, X.) I \/ >
= lim _> 0( K1/2 a(x) I X(t) I K1/2 a(x)) = cp(x, t); (7.24)
and evidently
lim o< VI ^(x, t) IV > = rc(x, t). (7.25)
According to (7.22), cp(x, t) satisfies the classical equation of motion, namely
(p(x, t) = Vo[cp(x, t)]. (7.26)
Let us present two examples:
Example 1. Ultralocal PseudoFree Theory
The quantum Hamiltonian of the ultralocal pseudofree field is given
H =  d3xj
dX B+(x,Wh(,W B(x,W
dX
82
where
+ m(y1/2)h .
The model function c(X) for the system is determined through (6.7b), and the
result is
(7.27)
Expressing the quantum Hamiltonian in terms of the renormalized
field operators, we have
1i
iflr (x) + im2Or (x)jd3x
H =
where we have defined the local operator
Obviously this definition means that nr neither fits into the canonical
framework nor fulfills the commutation relation [Or(x), nr(y)] = i H8(x y).
From the above analysis, the classical limit of the field operators in the
coherent states denoted by tp(x, t) and 7i(x,t) fits into the classical canonical
equation (7.22), with Vi((p) = 0, and (p(x, t) is the solution of the classical
pseudofree field equation of motion (7.26)20 :
83
cp(x, t) = 0cp'3(x,t) m2cp(x,t),
where the role of 0cp'3(x,t) is to assure that cp(x, t) > 0 or
that (p(x, t) is not allowed to cross through (p(x, t) = 0, This kind of solution can
be secured if we replace the above equation by the scalecovariant equation of
motion3
cp(x,t) [
For readers interested in the equation of motion of the pseudofree field
operators, Ref. 21 is recommended.
nrZ.
Example 2. Ultralocal Field with Interaction Potential g(p4 + tp6
2m 2
I *J
The quantum Hamiltonian is H = I d3x I d>. B+(x, X) h(, X) B(x, X),
dX
and the expressions of h(, X) and c(X) for such a model are
dX
w 3 N i Y(Y+1 )tÂ¡2 i ,2 .4 g2
h( *) = ^Px2 + 2 + ym2X + gX + SX
dX 2
2X
2m
,6 + m (Y 1/2 )fi + g ^m3l2)X2h
2 1 m
c(X) = L exp ( JmX2 X4
^JY H 2 4m
(7.28)
The Hamiltonian expressed in terms of the renormalized field operators is
84
H= (lrf(x) + i [m2 + 2g (Ym3/2)h ]
J \2 2 m 2 m2 I
2*2 2
with nr = d>r + y(y+1)/22 r + m(y)/jOr Since the last two terms in
h(, A,) vanish when we take the classical limit, according to (7.20), the
3A
corresponding classical Hamiltonian when /z > 0 is
Hci = I j^t2(x) + 0cp'2(x) + im2
J \2 2 2 m2 I
The canonical equations are
7t(x, t) = 0cp'3(x,t) m2(p(x,t) 4g(p3(x,t) 
and the equation of motion is
cp(x, t) = 0cp3(x,t) m2
according to (7.26).
^
m2
^
m2
(7.29)
Again the role of 0 0 or cp(x, t) < 0 ,
namely, that (p(x, t) is not allowed to cross through (p(x, t) = 0, This kind of
solution can be secured if we replace (7.29) by the scalecovariant equation of
motion3
(p(x,t)cp(x, t) = m2tp2(x,t) 4gcp4(x,t) 2
m2
which is satisfied by the classical limit of the ultralocal field
lim^ _> o< VI ^*r(x, t) I \j/ >, according to Eq. (7.24).
CHAPTER 8
PATHINTEGRAL FORMULATION OF ULTRALOCAL
MODELS
In an earlier chapter, we have pointed out that the pathintegral of the
quartic selfcoupled ultralocal scalar field leads to an trivial (Gaussian) result
when approached by the conventional lattice limit (Chap. 5). However, the
characterization of infinitely divisible distributions allows ultralocal models
alternative operator solutions (Chap. 6) which suggest a new expression of
pathintegral with a nonvanishing, nonclassical potential. In this chapter, we
seek to replace the standard lattice formulation by a nonstandard one which
admits nontrivial results. Specifically, we will use these alternative,
nonperturbative operator solutions to construct nontrivial latticespace path
integrals for nonrenormalizable ultralocal models. As we will see, the
indefinite, nonclassical, singular potential required for the nontriviality in
multicomponent case has different effects on distributions compared to the
singlecomponent case, however the essential property of reweighting the
distribution at the origin is similar. The appearance of additional
nonclasssical, singular potentials suggests that we can not always place the
classical Lagrangian or classical Hamiltonian directly into the pathintegral
formulation, or in other words, a straightforward canonical quantization of
fields with infinite degrees of freedom does not always apply.
86
8.1. Operator Solutions of Ultralocal Models
In this section, we will select certain results, which will be used here,
from Chapter 6 on the operator analysis of ultralocal models15, and put them
into completely proper dimensional forms. Following Chapter 6, the N
component ultralocal field operator can be expressed as
J
(x) = I dA B+(x, A,) A B(x, A)
(8.1)
Where the operators B+(x, A) and B(x, A) are translated Fock operators, defined
through B(x, A) = A(x, A) + c(A), A = while A+(x, A) and A(x, A) denote
conventional irreducible Fock representation operators for which I 0 > is the
unique vacuum, A(x, A) 10 > = 0. for all xeSR""1, Ae9N. The only
nonvanishing commutator is given by
A(x, A), A+(x', A') = 5(xx0 8(AA0.
(8.2)
Obviously, the operators B+(x, A) and B(x, A) follow the same commutation
relation (8.2). For the singlecomponent case, (8.1) becomes
0(x) =
l dA B+(x,
A) A B(x, A).
(8.3)
Renormalized products follow from the operator product expansion:
which suggests the definition of the renormalized square as
sbl
Orij(x) s b I dX B+(x, X) XiXj B(x,X) = ZOi(x)
(8.4)
Here we have introduced an auxiliary constant b designed to keep Z
dimensionless. (In the previous chapters, we have generally chosen b=l).
With [] = dimension (), we have [b]= [x]1_n. More generally, the
renormalized local powers of the field are given by
ii, ,ik = 1,2,3, N and k = 1,2,3,
Occasionally, we need to use the renormalized negative powers of the field
even though they are not local operators. Take the onecomponent case for
example:
dXB+(x,X) (bXj)kB(x,X) h J[Z 01(x)]k,
z
i = 1,2 N;
(8.6)
it can formally be extended to k < 0, as long as we define
89
The Hamiltonian of O(N) invariant, Ncomponent ultralocal fields can
be expressed as
dX B+(x, X) MV*, X) B(x, X)
dX A+(x, X) h(V\, X) A(x, X).
(8.7)
1 9 2
Where h(V^, X) = h V>. + V(X) is a selfadjoint operator in the X variable
alone. The connection between these two relations holds when we insist that
h(Vx, X) c(X) = 0, and in order for 10 > to be the unique ground state of H, it
follows that c(X) g Â£2(9tN). Since [c]2 = [x]1_n[X]N and [X]2= [x]n [h], we have
[c]2 = [x]1"n(1+N/2)[^]'N/2. Therefore, by taking into account of the dimensions,,
the model function may be expressed as
c(X) = ft(2rN)/4baX exp ( y(X, b, ft) j, (8.8)
! r r1 2 I
where a = [ n(lT+N/2)l ] /2(nl). With a proper account of dimensions, the
selfadjoint base Hamiltonian obeys
^ ^ 2
MV*, X) = M2V2x+ r(r+2~N>ft + m^(rN/2) + m2bX2+ lVi(Wt).
2b
2bX
(8.9)
Obviously, For the singlecomponent case, (8.8) and (8.9) become
Cft) = /Â¡W>/4bIn<3/2tfll/2
W
^mX2 y(X, b, h)
2 n
(8.10)
h0/ax, X) = h2 + 7(7+1 }^2 + mfi(Y 1/2) + lm2tA2 + lVi(bX) .
2b 9X2 2b/.2 2 b
(8.11)
The Hamiltonian may also be expressed in terms of renormalized
fields as
H =  jinr2(x) + Im20r2(x) + Vi[
22 2 0
where nr(x) = Or(x) + T(r+2 N)ft2b21 Or(x) I + mh (2T N)b I Or(x) I and in
terms of bare fields as
H=J jiZn2(x) + lm2ZiJ>2(x) + lVi[Z(x)]jdx (8.13)
^2 2 2 02
where Z (x) = Z0> (x) + r(r+2N)/z2b2Z'310(x) I + mh (2rN)bZ'11
For the singlecomponent case, the Hamiltonian becomes
H =
jln2(x) + im2chr2(x) + Vi[Or(x)] jdx,
(8.14)
Â¡Zn2(x) + lm2Z02(x) + lVi[Zr(x)] jdx
(8.15)
where n2 = d>2+ y(y+l)n2b2 mh(2y l)b Or and Zn2 = Z + 7(7+1 )^2b20>'2Z'3
+ m^(27l)b oV1 =U2r.
91
The Hamiltonian operator (8.7) readily leads to the Heisenberg field
operator which is given by
I
0(x,t) = e*H/
I
= dX B+(x, X) X(t) B(x, X)
(8.16)
After this partial review, we turn our attention to the pathintegral
formulation of ultralocal models.
92
8.2 EuclideanSpace PathIntegral Formulation of SingleComponent
Ultralocal Fields
In this section, we will start from the operator solution presented in
Â§8.1 to derive the Euclidean time latticespace formulation. Attention is
focused on the timeordered vacuum to vacuum expectation functional
il
C[f] = < 0 I Texpj UI dx dt 0(x,t) f(x,t)
I 0>.
(8.17)
Insert (8.3), then we have
C[f] = < 0 I Texd U
pj^j" dx dt J dX B+(x, X) f(x,t)X(t) B(x, X)
I 0>,
By using the normal ordering technique, C[f] becomes
< 0 IT: exp j dx J dX B+(x, X) { exp [jJ
X) { exp[E dt f(x,t)X(t)] 1} B(x, X)
I 0>.
Notice that only the part inside { } depends on time t Therefore we can
move the timeordering sign T into the bracket, so we find that
C[f] = < 0 I: exp
j dx j dX B+(x, X) { Texpl^j
X) { Texpl^J dt f(x,t)X(t)] 1 } B(x, X)
ici
= exp  dx  dX c(X) { Texpfh j dt f(x,t)A,(t)] 1} c(X)
ll
: I 0 >

Full Text 
LD
\'\$o
I ^ V
. 263
UNIVERSITY OF FLORIDA
3 1262 08554 5555
SINGULAR DYNAMICS
IN
QUANTUM MECHANICS AND QUANTUM FIELD THEORY
By
CHENGJUN ZHU
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
Dedicated to
My Parents and Friends
ACKNOWLEDGMENTS
I wish to thank my supervisor, Prof. J. R. Klauder, for his efforts, patience
and encouragement throughout the time I have been at the University of Florida.
He introduced me to most of the topics involved in this dissertation and always
was ready for a discussion if needed. Over the years, his enthusiasm and
encouragement have been constant sources of inspiration to push the project
forward.
I am grateful to the other members in my supervisory committee, Prof.
Pierre Ramond for his valuable comments and suggestions, Prof. Charles
Hooper, Prof. Robert Buchler, Prof. David Tanner and Prof. Christopher Stark,
for patiently sitting through my oral exam and thesis defense. Special thanks
should go to Prof. Buchler for his kindness, concern and heuristic suggestions
when I was very depressed in jobhunting.
Also I want to express my deep thanks to my fellow graduate students
and colleagues, for their help and encouragement throughout the years.
TABLE OF CONTENTS
pages
ACKNOWLEDGMENTS iii
ABSTRACT vi
PART I CLASSICAL SYMPTOMS OF QUANTUM ILLNESSES
CHAPTERS
1 INTRODUCTION 2
1.1 Basic Concepts of Operator Theory 3
1.2 Symmetric Operators and Extensions 4
1.3 The Construction of SelfAdjoint Extensions 8
2 CLASSICAL SYMPTOMS OF QUANTUM ILLNESSES 10
2.1 Principal Assertions 10
2.2 Classical Symptoms of Quantum Illnesses 12
2.3 More General Examples 16
2.3.1 Examples of OneDimensional Hamiltonians 16
2.3.2 Examples of ThreeDimensional Hamiltonians 20
3 SELFADJOINTNESS OF HERMITIAN HAMILTONIANS 22
3.1 Three Different Cases of Hermitian Hamiltonians 22
3.2 The Application of Boundary Conditions and SelfAdjoint
Extensions at Regular Points 32
3.3 The Application of Boundary Conditions and SelfAdjoint
Extensions at Singular Points 34
3.4 Conclusion 38
PART II OPERATOR ANALYSIS AND FUNCTIONAL INTEGRAL
REPRESENTATION OF NONRENORMALIZABLE MULTI
COMPONENT ULTRALOCAL MODELS
4 INTRODUCTION 44
5 CLASSICAL ULTRALOCAL MODEL AND THE STANDARD
LATTICE APPROACH 48
6 OPERATOR ANALYSIS OF MULTICOMPONENT ULTRALOCAL
MODELS 53
IV
6.1 Operator Analysis of SingleComponent Ultralocal Models
54
6.2 Operator Analysis of FiniteComponent Ultralocal Fields
60
6.3 Operator Analysis of Infinitecomponent Ultralocal Fields
65
7 THE CLASSICAL LIMIT OF ULTRALOCAL MODELS 73
7.1 Ultralocal Fields and Its Associated Coherent States 74
7.2 Selection of the Coherent States for Ultralocal Fields
and the Classical Limit 77
8 PATHINTEGRAL FORMULATION OF ULTRALOCAL MODELS
86
8.1 Operator Solutions of Ultralocal Models 87
8.2 EuclideanSpace PathIntegral Formulation of
SingleComponent Ultralocal Fields 92
8.3 EuclideanSpace PathIntegral Formulation of
MultiComponent Ultralocal Fields 96
REFERENCES 101
BIOGRAPHICAL SKETCH 103
v
Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
SINGULAR DYNAMICS
IN
QUANTUM MECHANICS AND QUANTUM HELD THEORY
By
Chengjun Zhu
April, 1994
Chairman: Dr. John R. Klauder
Major Department: Physics
The classical viewpoint that the pathologies of quantum Hamiltonians are
reflected in their classical counterparts and in the solution of the associated
classical dynamics is illustrated through the properties of classical equations of
motion. Rigorous mathematical proofs are provided by calculating the
deficiency indices, which further help to analyze the possibility of extending the
Hermitian Hamiltonian to a selfadjoint one. A few examples of how to add
boundary conditions on wave functions in order to have selfadjoint extensions,
as well as to cure the illness of certain Hamiltonians, are discussed.
The nontrivial (nonGaussian), nonperturbative quantum field theory of
0(N)invariant multicomponent, nonrenormalizable ultralocal models is
presented. An indefinite nonclassical and singular potential has replaced the
nonvanishing, positivedefinite nonclassical and singular potential appeared in
the singlecomponent case. The operator theory of multicomponent ultralocal
vi
fields remains noncanonical even with the disappearance of the singular
potential. The validity of this nontrivial solution is supported by the fact that the
nontrivial quantum solution reduces to the correct classical theory in a suitable
limit as fi 0. The nontrivial (nonGaussian) path integral formulation
constructed by the nonperturbative operator solution, involving the nonclassical
and singular potential, replaces the standard lattice approach, which invariably
leads to a Gaussian theory regardless of any nonlinear interactions. The
appearance of the nonclasssical, singular potential suggests that we can not
always place the classical Lagrangian or classical Hamiltonian directly into the
pathintegral formulation, or in other words, a straightforward canonical
quantization of fields with infinite degrees of freedom does not always apply.
These differences suggest plausible modifications in the latticespace formulation
of relativistic nonrenormalizable models that may lead to nontriviality for N
4
component models such as On, n > 5 (and possibly n = 4), for N > 1.
Vll
PARTI
CLASSICAL SYMPTOMS
OF
QUANTUM ILLNESSES
CHAPTER 1
INTRODUCTION
The rules of quantization, as laid down in 1926 by Schrodinger, have stood
the test of time and have provided the basis for applying (and teaching)
nonrelativistic quantum mechanics1. Because of the overwhelming success of the
theory, it is not surprising that physicists have little use for several mathematical
niceties that go by the largely unfamiliar code words of "selfadjoint extension,"
"deficiency indices," " operator domains," etc. (which we will briefly define in
subsequent sections). 2/3
These concepts typically become important when the quantization
prescriptions are ambiguous or otherwise incomplete all by themselves4. Our
goal is to show that such quantum technicalities are actually reflected in the
classical theory by corresponding difficulties that are easy to see and understand.
It will be clear that such an evident classical difficulty must lead to some kind of
quantum difficulty, and thus the naturalness of the corresponding quantum
technicality will become apparent. We may go so far as to assert that there are
sufficient classical symptoms of any quantum illness that a complete diagnosis is
possible already at the classical level (Chapter 2). Of course, resolving the
problems and effecting a full cure, when one exists, can only take place at the
quantum level (Chapter 3).
This chapter contains basically a summary of the mathematical concepts
and theorems prepared for later chapters. In Chapter 2, we will discuss the
properties of classical solutions of given examples, whose "symptoms" can be
2
3
used to diagnose any potential quantum "illnesses". In Chapter 3, we will
provide the mathematical proof for all the assertions made in Chapter 2 and will
also give a few examples of how to add boundary conditions on the wave
functions in order to extend the Hamiltonians to be selfadjoint and so to cure the
illness of certain Hamiltonians.
1.1 Basic Concepts of Operator Theory
In this section we follow Ref. 3 closely. The operators we deal with in
quantum mechanics are frequently unbounded operators which need to be
defined on a domain D(A) to ensure that Ay/e for y/ e D(A), where 9{is
Hilbert space.
Generally, if A and B are two unbounded linear operators,
a,p e C,
y/e D (ocA + (5B).
D (aA + pB) = D(A) n D(B),
(aA + pB)y/ = a (A y/) + /3(B y/),
For the product put
D(AB) = {y/:y/eD(B), By/ eD(A)},
(AB)y/=A(By/)f y/e D (AB).
In general D(AB) * D(BA), and hence AB * BA, and even A A'1 * A'1 A,
because their domains may not coincide. So extra care is needed in treating these
operators.
4
We recall that A is densely defined in #if (and only if) jtfis the closure of
D(A), i. e., for y/ e ?{, there is a sequence of elements of D(A) converting to y/,
[fa +yf, fa e D(A)].
For a densely defined operator A for iH into there exists a unique
adjoint operator A+ which satisfies
(A yi,
where y/ e D(A) and 0 e D{A +).
If an adjoint operator A+ = A on D(A), and D(A) = D(A+), then A is called
a selfadjoint operator.
1.2 Symmetric Operators and Extensions
If A* = A on D(A), then D(A) Â£ D (A*) always holds (like Hermitian
Hamiltonian operators). Now,
(a) A is called a selfadjoint operator when D(A) = D(A+), and one writes A = Af.
(b) A is called a symmetric operator when D(A) c D(A+), and one writes A c A+.
Further, if there exists a symmetric extension As of A, such that A c As =
As+ c A+, then we say that A has the selfadjoint extension As (by enlarging D(A)
to D(AS) and contracting D(A+) to D(AS+) = D(AS)).
Let A + 01= Â±i 0t, with solutions QÂ± e NÂ± which are closed subspaces of ^4
known as the deficiency spaces of A; and their dimensions, nÂ± respectively, are
called the deficiency indices. We shall also say for brevity that A has deficiency
indices (n+, n_).
Lemma 1. If A is symmetric, then D(A'1â€™) = D( A )Â®N+Â®N., A denotes the
closure of A.
5
Lemma 2 A symmetric operator with finite deficiency indices has a self
adjoint extension if and only if its deficiency indices are equal.
With the help of the two above Lemmas, the following theorem regarding
deficiency indices is straightforward:
THEOREM 1: Suppose the Hermitian operator A has deficiency indices
(n+, n_), then if
(i) n+ = n. = 0,A is selfadjoint when D(A) is closed and the closure of A is self
adjoint when D{A) is not closed.
(ii) n+ = n * 0, A has selfadjoint extensions.
(iii) n+ * n., A is not selfadjoint and has no selfadjoint extension.
This theorem is used to classify Hermitian operators, and we see that not all
Hermitian operators will generate fulltime quantum mechanical solutions.
Example: A =  id/dx on LiiP)
A + Â±= Â±i 0Â±,
Ai=i d/dx,
0t(x) ~ exp(+ x).
(a) Q = ( + Â«): Neither 0+ nor 0. is in Â°o, + <*>), so n+ = n = 0 and A is
selfadjoint on its natural domain. This fact is consistent with its classical
behavior (see Fig. 1(a)), where there is a fulltime evolution.
(b) Q = [ 0, + Â«o): 0. = exp(x) is not in LÂ¿([ 0, + Â«>)), so (n+, n.) = (1, 0), A is
not selfadjoint and possesses no selfadjoint extension. This fact is consistent
with its classical behavior (see Fig. 1(b)), where there is no fulltime evolution.
(c) Q = [ 0,1]: Both Â± are in Â£^([ 0,1 ]), (n+, ru) = (1,1), A has selfadjoint
extensions by adding the boundary condition y/(l) = exp (iff) yKO), where 8e 9Ã.
6
The spectrum of A = 6 + 2n n, n = 0, Â± 1, Â± 2,.... For different 6, we get a different
selfadjoint extension. The case of 6 = 0 is the usual case used in quantum
mechanics and is called the periodic boundary condition. See Fig. 1(c) for its
consistent classical behavior.
The deficiency indices are clearly of central importance in the classification
of Hermitian operators and in the construction of selfadjoint extensions. These
may be found easily if explicit solutions of A fy/Â± = Â± i \Â¡rÂ± are known, but unless
the coefficients of A are simple, the calculations will involve difficult special
functions. In order to avoid those tedious, sometimes even impossible
calculations, we will use a modified theorem of deficiency indices, especially
when both end points of Â£2 are singular. First, let us look at an example with
quantum Hamiltonian H, where
2
H \f/=(p2 + x3)\i/=(^ + x3)y/
dx2
acting on functions defined on an interval Ã2 = (<Â»,+ Â°Â°). Both end points x = Â± Â°Â°
are singular. A direct calculation of the deficiency indices seems incredibly
tedious since the behavior of a solution of Hi//Â± = Â± i y/Â± at both end points must
be known. To simplify the difficulties, we separate Q = (a, b), where a and b are
both singular, to two intervals with Q\ = (a, c ] and Qi = [ c, b), where c is a
regular point. Here comes the second theorem regarding deficiency indices:
THEOREM 2 Let Aa and A\, be symmetric operators associated with A on
Q\ and / respectively. If nÂ±, nÂ±a, nÂ±b indicate the deficiency indices of A, Aa
and Ab , respectively, then nÂ±= n^ + nÂ±b  2, respectively (see Chapter 2 of Ref.
3).
To apply this result to the above example, we have
Since H is a real operator, i. e., H * = H, we have y/. = yC. So n+= n. and we only
need to consider y/+ and n+. Let 1/4 = yr,
2
(f+ X3)l//= I>.
ax2
The asymptotic behaviors at x Â»Â± Â°Â° is given by
yi  *V = 0
V4~ Vx Ki/5(Â§*5/2) ~ x"3/4exp(  Jx5/2)
5 5
.Â» ~ VRZi/sCgW572) ~ W3/4cos (xp/2
â€ž ~ VR Ni/5(^xf/2) ~ w 3/4sin( ^j5/2
5 5 20
where ]\, N\ and Xy are the Bessel functions of the first and second kinds,
respectively. Obviously, the integration
( yKxfdx
converges at x = +
Thus, h+ +00= 1. In the same way,
8
(1 2)
so that both solutions of satisfy
j y/ixtfdx converges at x = 
Therefore, n+.0 = 2, and
n+ n+i +oo + Â«+,. *  2 = 1 + 2  2 = 1
(n+, n.) = (1,1).
One boundary condition* is needed to extend H to be selfadjoint. The existence
of bound states yioo demonstrates that the energy spectrum is discrete. This
result is exactly what is claimed in Chapter 2.
Later in Chapter 3, we will see examples for three different cases of the
deficiency indices: (i) n+= n. = 0, (ii) n+= n. * 0, and (iii) n+* n..
1.3 The Construction of SelfAdjoint Extensions
Before we construct the selfadjoint extensions, we introduce some
notation (see Chapter 10 of Ref. 3):
(i) [(f), y/) = 04 , y/)  (0, A*y/), where D(A +);
(h) f\r fi â€¢" fn e D(A +)= D{A) Â®N+Â©N_, where fÂ¡ = h{ + fa i= 1,2,...,
hj e D(A), 0, â‚¬ N+0N..
If n+= n. , the number of boundary conditions = n+; see page 260 of Ref 3.
9
We call fi, fi â€¢â€¢â€¢ fn linearly independent relative to D(A) if fa, fa, ..., fa are
linearly independent.
With the help of the preceding definitions, we introduce the following
theorem:
THEOREM 3 Let A be a symmetric operator with finite nonzero deficiency
indices n+ = n.= n. Suppose that f\, f2 â€¢â€¢â€¢ /â€ž â‚¬ D(/4+) are linearly independent
relative to D{A) and satisfy
(fi,f,)= 0 (1,7 = 1,2, n).
Then the subspace Mof ^consisting of all y/e DiA*) such that (\j/,ft) = 0 (i = 1,2,
n) is the domain of a selfadjoint extension M of A, given by M y/= Afyj for
y/eM.
{yf, fi) = 0, i = 1, 2,n, are called the number of n boundary conditions on
the wave function yj.
In chapter 3, we will give a few examples of how to use theorem 3 to
obtain some of these selfadjoint extensions and thereby cure the illness of certain
Hamiltonians.
CHAPTER 2
CLASSICAL SYMPTOMS OF QUANTUM ILLNESSES
Without using the precise definitions and techniques of operator theory,
presented in chapter 1, we can simply show that the pathologies of quantum
Hamiltonians are reflected in their classical counterparts and in the solutions of
the associated classical equations of motion. This property permits one, on the
one hand, to appreciate the role of certain technical requirements acceptable
quantum Hamiltonian must satisfy, and, on the other hand, enables one to
recognize potentially troublesome quantum systems merely by examining the
classical systems.
In Â§2.1, we will make the principal assertions that three categories of
classical solutions correspond to three categories of the selfadjointness of
quantum Hamiltonian operators. Examples are given in Â§2.2 and Â§2.3, while the
mathematical proof will be presented in chapter 3.
2.1 Principal Assertions
H =
Pâ€˜
2m
Specifically, for the classical system with a real Hamiltonian function
+ V(q), the classical equation of motion
mq'(t) =  V'[q(t)]
admits two kinds of solution:
(i) q(t) is global (which is defined through Â°o < t < +<Â») and unique, e. g.,
H = p2 + i?4 ;
10
11
(ii) q(t) is locally unique, but globally possibly nonexistent (escapes to infinity
in finite time). This case may be also divided into two subcases:
extendible (q(t) can be extended to a global solution) or nonextendible.
For example, H = p2  qA, H = p2 Â± q3 are extendible, but H = pq3 belongs
to nonextendible situation.
The corresponding quantum mechanical problem
i/Â¿yKx, t) = HyKx, t) = [  //2 d2 + v(x) ] i/Kx, t)
ot 2m dx 2
has similar cases. To conserve probability, the time evolution of the wave
function must be effected by a unitary transformation. A unitary transformation
gives a prescription for wave function evolution for all times t,  Â°Â° < t < or as
we shall sometimes also say, for full time. The generator of such a unitary
transformation times V^T, which we identify with the Hamiltonian operator (up
to constants), must satisfy one fundamental property, namely, that of being "self
adjoint." Being selfadjoint is stronger, i.e., more restrictive, than being
Hermitian, which is the generally accepted sufficient criterion. According to
Theorem 1 on page 5, typically, there are three qualitatively different outcomes
that may arise (i) no additional input is needed to make the Hamiltonian self
adjoint; (ii) some additional input (i.e., the boundary conditions) is required to
make the Hamiltonian selfadjoint, and qualitatively different Hamiltonians may
thereby emerge depending on what choice is make for the needed input; and (iii)
no amount of additional input can ever make the Hermitian Hamiltonian into a
selfadjoint operator. Remember it is only selfadjoint Hamiltonians that have
fully consistent dynamical solutions for all time. Thus in case (iii) no acceptable
quantum dynamical solution exists in any conventional sense.
12
Therefore we make the general assertions that there are three categories of
classical solutions, which correspond to three categories of the selfadjointness of
quantum Hamiltonian operators:
Â£(0
Hamiltonian operator
selfadjoint & unique
selfadjoint extensions exist
no selfadjoint H exists
(i) global & unique
(ii) nonglobal but extendible
(iii) nonglobal & nonextendible
2.2 Classical Symptoms of Quantum Illnesses
To be sure, the majority of classical systems one normally encounters~as
represented by their classical Hamiltonians, their Hamiltonian equations of
motion, and the solution to these equations of motionare trouble free. But there
are exceptions, classical systems which exhibit one or another kind of singularity
in their solutions, and it is in these problematic examples that we will find the
anomalous behavior we seek to illustrate.
Let us consider three model classical Hamiltonians that will exhibit the
three kinds of behavior alluded to above.
Example a:
H = â€”p ^ 4.
2y 41
The equations of motion lead to
13
where E > 0 is the conserved energy. Nontrivial motion requires E > 0 and E >
^4/4 in which case
leads to a welldefined, unique solution valid for all time. This solution exhibits
a periodic behavior with an energy dependent period T(E). See example a in
Table I.
Example b:
H=2p2 + 3
The equations of motion lead to
42 = 2E
and E can assume any real value. Since cp < 3E, we find that
da
Â± . ^ t + c.
J
This solution has the property that cj diverges, c\  <*>, for finite times, for
any nonzero E; see the solid line of example b in the table. The indicator of this
behavior is the observation that the integral converges as the upper limit goes to
 oo leading to a finite value for the right side, namely, a finite value for the time.
Actually, this same trajectory diverges at an earlier time as well. As b illustrates,
14
the particle comes in from q =  Â®o at some time, say t = to, and returns to q = Â«Â» at
a later time, say T + to, where
0E)'/3
dq
T = 2
For any nonzero E, T < Â°Â°; in particular, by a change of variables, we learn that
where S(E) = E/ IEI, the sign of the energy. As I EI Â» 0 the particle spends more
and more time near q = 0, until, at E = 0, it takes an infinite amount of time to
reach (or leave) the origin.
Example b in the table illustrates the generic situation for E * 0 and finite
T. How could one possibly expect the quantum theory to persist for all time
when the generic classical solution diverges at finite times? The only possible
way for this example to have a genuine quantum mechanics is for the particle to
enjoy a fulltime classical solution. And to achieve thatand this is the important
pointwhenever the particle reaches q =  Â°o, we must launch the particle back
toward the origin with the same energy, once again follow the trajectory inward,
and then outward, until the particle again reaches q =  when we must again
launch the particle back toward the origin with the same energy,..., and so on,
both forward and backward in time ad infinitum. In brief, to get fulltime classical
solutions (as needed to parallel full time quantum solutions) we must recycle the
15
same divergent trajectory over and over again in an endless periodic fashion
(with period T(E)); see b in the table with the solid and the dashed lines.
Example c:
H = p q3.
The equations of motion, in this case, lead to
4 =<73,
with the solution
q(t) = Â± l/Yc21.
The solution is valid for t < c/2, diverges at t = c/2, and becomes imaginary for t >
c/2. See example c in the table, where we chose the constant c = 0. In no way can
an imaginary solution be acceptable as a classical trajectory. We cannot relaunch
the particle once it has reached q = Â± Â°Â° at t = c/2 following the kind of solution
we have found, the only solution there is, as we were able to do in case b. In
short there is no possibility to have a fulltime classical solution in the present
example.
If there is no fulltime classical solution, then there should be no fulltime
quantum solution, and that is exactly what happens. The corresponding
quantum Hamiltonian may be chosen as Hermitian, but there are no technical
tricks that can ever make it selfadjoint. Once again, the signal of this quantum
behavior can be seen in the classical theory, i.e., a divergence of the classical
16
solution followed by a change of that classical solution from real to imaginary.
With such a classical symptom, it is no wonder that there is an incurable
quantum illness.
2.3 More General Examples
In what follows we discuss a number of hypothetical classical
Hamiltonians, examine qualitatively the nature of their classical solutions, and
address, based on the thesis illustrated in Sec. 2.1, the problem of making an
Hermitian Hamiltonian into a selfadjoint one, if that is indeed possible.
Let us dispense with the "healthy" cases at the outset. Whenever the
classical equations of motion admit global solution for arbitrary initial conditions,
then the quantization procedure is unambiguous (apart from classically
unresolvable factorordering ambiguities). Observe that the existence of such
global solutions is an intrinsic property of a Hamiltonian independent of any
particular set of canonical coordinates.
2.3.1. Examples of OneDimensional Hamiltonians
q=p = Â±Ã2 VE + <74,
ÃI'JE + q4
dq
= Â±t +c.
Example d:
17
E can be any real value.
For E > 0, we notice that dq / Ã2 VE + qA converges to, say T (E), which
means when the particle travels from  Â« to + the time interval is T (E). For
nonzero E, T is finite; see the solid line of example d in the table. In order to get a
fulltime classical behavior, we must send the particle back when it gets q = Â± oÂ°;
see the two distinct dashed lines of d in the table. In quantum theory, this
situation corresponds to adding two boundary conditions (at q = Â± Â°Â°), which are
required to extend H to be selfadjoint.
For E < 0, the paths do not cross the origin, but there is no essential
difference in the quantum behavior from the case E > 0. That means we still need
to add two boundary conditions to extend H to be selfadjoint.
Example e:
h=2v2q2'
q=p = Â±Ã2 jE + ql,
(1/Ã2) In  q + Vi/2 + E  = Â±f + c.
When the particle travels from  Â«> to + Â«Â», the time spent by the particle spans the
whole faxis (see example e in the table), so there is a global solution for an
18
arbitrary initial condition. Thus the quantum Hamiltonian is unique and self
adjoint.
Since there is no periodic behavior, the spectrum of the quantum
Hamiltonian is continuous.
Example f.
H = 2pq2
2cj = l/(t + c).
Global solutions exist (see example / in the table) and the quantum Hamiltonian
is selfadjoint. Since there is no periodic behavior the spectrum is continuous.
Example g:
H =2p (1/q),
consider Â£2 = ( <*>, 0) or (0, + Â«),
4 = 2(1/*),
q2 = 4t + c.
19
similar to Example c, q becomes imaginary for t <  c /4, and there is no
possibility of having a fulltime classical solution, just as in the case of example c.
Therefore there is no way to extend the Hamiltonian to be selfadjoint.
Example h:
H = p2 + 2pq3,
q=2(p + q3) = Â±2 Jq6 + E.
Its classical solution is similar to example d, and is identical to H = p2  q6' to
which it is canonically equivalent.
Example i:
H = p2 + 2p /q
q * 0, so Â£2 = ( <*>, 0) or (0, + <Â»),
q=2(p + \/q) = Â±2 jE + l/q2,
Vl +Eq2 =Â±2E(t+c).
The solution to the motion reads
(2E)\t + c)2  E q2 = 1.
20
See example i in the table, where we chose E > 0. Since cÂ¡ = 0 is a singular point,
we divide SR into Q = ( <*>, 0) and (0, + <*>). For example, when the particle reaches
(j > 0+, we have to send it back or cross over cÂ¡ = 0 to get a fulltime classical
behavior. By choosing c, the fulltime classical picture may be like the solid and
dashed lines of i in the table. In quantum theory, one boundary condition is
needed to extend H to be selfadjoint.
Two additional examples (/ and m ) appear in the table without discussion
in the text.
2.3.2. Examples of ThreeDimensional Hamiltonians
To simplify the problem, we consider here only central potentials V{r). In
suitable units, the quantum Hamiltonian becomes
H =  V2 + V(r),
v2_ 1 drid L2
r2dr dr r2
Set
V/Â«,
then
Hr =  + ^4^ + V{r) for u(r).
dr1 rÂ¿
The condition that i l\yl2 d3r converges now becomes the condition that
Qu(r)fdr converges.
For V(r) =  A /rn, n = 1,2,3,..., A >0,
21
Hr = p?(X /rn) + (/ (/ + l)/r 2)
and the classical equation of motion is
f = 2VE + (A/râ€)(/ (/ + l)/r2).
Under both cases of E < 0 and E > 0, we see the difference between Â« = 1 and
n > 2. For n > 2, near the origin, i.e., r ~ 0,r ~ 2 Ye + A /r", so r could go as near
as r ~ 0. See example k in the table. In quantum theory, one condition is
required to extend the Hamiltonians to be selfadjoint. It corresponds to one
parameter (e.g., see parameter B in Ref. 4), which is needed to specify quantum
solutions. But for n=1, f = 2Ve + A /r  (/ + l)/r2; with E < 0 and / > 0, the
motion oscillates between the two roots of the expression under the radical,
namely,
/(/+!)
E
1(1+1)
E
So it avoids the singular point r = 0, and therefore it has a fulltime classical
evolution (see example j in the table), thus its quantum Hamiltonian is a self
adjoint operator. That is why the hydrogen atom does not have any problems.
CHAPTER 3
SELFADJOINTNESS OF HERMITIAN HAMILTONIANS
Having recalled that simple and physically natural classical "symptoms"
are available to diagnose any potential quantum "illness," we now discuss some
of the standard techniques in Chapter 1 used to analyze Hamiltonian operators
and confirm that the classical viewpoint presented in Chapter 2 is fully in
agreement with conventional analyses.
In particular, we analyze in this chapter the selfadjointness of several
Hamiltonians which appeared in Chapter 2 by calculating their deficiency
indices directly. Therefore, we can verify the consistency of solutions of classical
and quantum Hamiltonians. According to Theorem 1 on page 5, we have three
different cases of the deficiency indices: (i) n+= n. = 0, (ii) n+= n. * 0, and (iii)
n+* n.. Cases (i) and (iii) are simple, where either a densely defined operator is
or is not selfadjoint, but case (ii) is much more complicated. Discussions such as
how to add boundary conditions on the wave functions in order to extend the
Hamiltonians to be selfadjoint, and what kind of physical interpretation those
extensions imply, etc., will be presented in Â§3.2 and Â§3.3.
3.1 Three Different Cases of Hermitian Hamiltonians
In this section we will apply Theorem si & 2 to four general types of
Hamiltonian, just as we did in Â§1.2 for H = p2 + x3:
22
23
(1) H = p2bxm,
(2) H = p xm + xm p,
(3) H = p2 + p xm + xm p,
(4) H = p2 + xpm +pmx
where m is a positive integer and b is a real constant. Those four types of H cover
all the Hamiltonians discussed in chapter 2.
3.1.1 H = P2  bxm
Obviously, H is Hermitian. Similarly to what we did for H = p2 + x3 in
Â§1.2,let
H+1/4= Â±Ã V4
withp =  id /Ax,
(Â£i + bxm)'t'Â± = + iV'Â±
As both b and m are real, \\f. = 1/4 . Thus, n+ = n. = n. So consider t/4 only; we
write
(^+focÂ»)vr=!>.
The asymptotic behavior of this equation as x > Â± is given by
1/ + bx mt// = 0
since we require y/ (<Â») = 0. The solutions are given by Bessel functions:
24
yKx) ~ VJxf Zi/(m + 2)( 2 ^ Vxm+2)
m + Z
where Zv ~ /v, Nv, /v, or Xv, which are Bessel functions of the first and second
kinds, respectively. To examine whether or not \ I y/(x) 12dx converges at x > Â°Â°,
we need to use the following asymptotic forms of the Bessel functions:
i y I Â» + ~,
2 2J
NUy)~
fv(y)~p=exp(y)
V2/ry
Kv(y) ~Vfexp(y)
If J I y/Or) I 2dx converges, then iyÂ±(x) e D(H+) c ^.
Examples:
(a) H = p2 +X4 :
y " x4y/= iyj
near Ixl ~ <Â», y/ 0; thus,
y/' xA\(/= 0.
25
Then b =  1 and m = 4. We should choose Z ~ IV/ Kv (with y = 1/3 I x 13), the
Bessel functions of the second kind.
For x ~ Â± oo, y/(x) ~ so n+/ ^ = 1
n+ = n+# +00 + n+r.Â«,  2 = 1 + 1  2 = 0 = n., i. e., (n+, n.) = (0,0).
Thus, H is selfadjoint in  <*>, + Â°Â°)), which makes possible the global solution
of the Schrodinger evolution equation (see Sections 9.6 and 9.7 of Ref. 3); the
existence of the bound states 1/4 and iy_ implies a discrete spectrum of energy.
(b) H = p2x4 :
y/' + xAy/= iy/
Here b = +1 and m = 4; thus
vÂ£2)(x)~Vx/i/6(1*3) and VxNi/6(ix3) ~ (l/x)cos or sin (ix3  }k).
w/ J
It is easy to check that both of the solutions are in Â£4, so n+ +co = 2 = n+>. ^ as yris
symmetric on x.
n+ = 2 + 2 2 = 2 = n., i.e., (n+, n.) = (2,2).
Two boundary conditions are required to extend H to be selfadjoint, and a
discrete energy spectrum is expected.
Indeed, even a WKB analysis leads to a discrete spectrum.
/v will make the integral diverge, and therefore is not allowed.
26
(c) H = p2 x2 (p2 + x2 is similar to p2 + x4 )
y + x2y= iy
where b = 1 and m = 2.
vt 2\x) ~ VR/i/4(^2) and i^Ni/A(]x2) ~ \41/2cos or sin {\xA  2tt)
T 4 4 4 8
but neither of them are in Â£2^); therefore,
(n+, n.) = (0, 0)
and H is selfadjoint, but its spectrum is continuous because no bound states
exist. Again, this conclusion follows from WKB arguments as well.
(d) H =p2 + x (p2  x is basically the same )
y'xy+ =  iy+
wl  (x i)y+ = 0.
For x > 0, b = 1 and m = 1,
y+(x) ~ 1xiKV3(kx if'2),
O
which is in Lq_.
27
But for x < 0, b = + 1, and m = 1,
V?' 2)(*) ~ Vx + i /i/3(
where we have ignored the unimportant phase term. Both of the solutions are
not in L2 (the square integral of y/+ diverges at x ~  Â°Â°). That means there is no
solution for x < 0, and no solution could be connected to yr+, x >0 either.
Therefore, we have
(i) (n+r n.) = (0,0) for Q = (Â«, 0),
(ii) (n+, n.) = (0,0) for Q = ( <*>, + oo);
(iii) (n+, n.) = (1,1) for Q = [ 0, + Â»).
The spectrum is expected to be continuous in (i) and (ii), but discrete in (iii).
This is an interesting system. In section 3.2, we apply it to a particle in a
gravitational field and a uniform electrical field.
3.1.2 H = pxm +x Wp
By substituting p ~  i d/dx and using [p,rm]=irnrm'1,we get
(p xm + x m p )!//+= (2p xm  imx m'1 )y/Â±= Â±i y/Â±
/
2xmy/Â± = (+1 mxm A)y/Â±
(i) m = 1, 2xy/Â± = (+1  l)y/Â±f
2x\i/+ = 2y/+,
xy/.0
28
with V4 ~ 1 /x., which is not in La since it diverges too rapidly at x ~ 0, and y/. =
const., which is not in La either. Therefore,
(n+, n.) = (0,0)
Thus, H = px + xp is selfadjoint and its spectrum is continuous.
(ii) m > 1,
2y/ /y/Â± = (+\
y/Â± ~ W' w/2exp (Â± 1 x1 m)
2(ml)
As x ~ Â± , y/Â± ~ 1 /[xj"w/2, which are square integrable, so Â± are regular points.
But now x = 0 is a singular point. Checking y/Â± near x = 0, we find
m = odd, n. = 1, n+ = 0, which has no selfadjoint extension. H is not self
adjoint and has no complete evolution, just as was the case for H = p x3 + x3 p in
Chapter 2.
m = even, n. = n+ = 0, H is selfadjoint with continuous spectrum. See the
example of H = p x2 + x2 p in the previous chapter.
It is interesting to point out that for L2 = (Â», 0), (Â«+, n.) = (0,1) if m = odd
and (1, 0) if m = even; for Q = ( 0, + Â«), (n+, n.) = (0,1) if m = odd and (0,1) if m =
even. Therefore, H is not selfadjoint in both L2 = ( Â«>, 0) and Q. = ( 0, + <*>), no
matter whether m is even or odd. To explain that by the classical picture (see
example c in the table), we say that neither of those intervals could contain a
complete temporal evolution.
29
3 \ 3 H = p^ + p x^i + x p
In the above section, we found that p xm + xm p is not selfadjoint if m =
odd. Here we will show that by adding p2 to it, the situation will be changed
dramatically. First let us examine the classical solutions:*
H = p2 + p cjm +cÂ¡mp = p2+2pcÂ¡rn
Cj=2p + 2qm = Â±2 ^E + cj^m
(i) If m = 1, the solution is like that for H = p2  cÂ¡2, where H is selfadjoint.
(ii) If m > 1, the solution is similar to that for H = p2 q4, where boundary
conditions must be added to make H selfadjoint.
Second, let us see that quantum features of H:
H = p2 + pxm +xmp = p2 + 2pxm imx m _1
[p 2+ 2p x m  imx m A)y/Â± = Â±i y/Â±
yÂ± + 2i xmy/Â±+ imx mAy/Â± = + iy/Â±
The asymptotic for near x ~ Â± Â°o is
// t
y/Â± + 2i xmy/Â±+ imx = 0.
H =p2+ 2p cÂ¡m, 2p =  2qm Â± 2 VÂ£ + q2m , 2p + 2pm= Â±2 Ve +
30
We introduce an equation with the solution given by the Bessel functions, i.e.,
O +[(1  2a)/x + 2ifiyxYl]0 + [(a2 v2?2)/*2? i/3)(y 2a)x r2] 0= 0
0 = xaexp (Â±ipx y) Zvifay).
Note that 1/4 just fits this equation by choosing
a =1/2, y=m + 1, P = 1/y, v=l/2(m + l),
1/4Â» ~ Vjxjexp ( iâ€”1â€”xm + 1) Zv (â€”1â€”xâ„¢ + 1) ~ 1/Vlxfâ€
m + 1 m + 1
which is square integrable when m> l*. So n+ Â±co = Â«. Â±00 = 2, and
(Â«+, n.) = (2,2), when m > 1.
So by adding p2, H always has selfadjoint extensions no matter whether m is
even or odd. This is exactly consistent with what we have just discussed from
the classical point of view.
As for the case m = 1, 1/4 ~ 1/Vpc[, which is not square integrable, so
(n+, M.) = (0, 0), which again agrees with what follows from the classical point of
view.
3 \ 4 H = p 2 + x p tri + p tn x
Classical method:
* Here Zv /n, Nv.
31
p =  dH/dcj =  2 pm
which is similar to cÂ¡ = 2 q m based on H = 2 p qm; therefore,
when m = even, H is selfadjoint;
when m = odd, H is not selfadjoint.
Quantum method:
x Â» id/dp, [x, pm] = imp m 1
(p2 + xpm +pmx )y/Â±(p) = Â± i y/Â±(p)
/
2ip my/Â± = (Â±i  p2  imp
y/Â±~ (l/V^p*") exp + 2(^_ p1  mj x exp  i 2{Â£^ P 3'm) (31)
For m > 1: (n+, Â«.) = (0, 0), if m = even,
(n+, n.) = (1, 0), if m = odd.
For m = 1, (n+, n.) = (0, 0) which has already been discussed in Section 3.1.3. We
see again that the classical picture is consistent with the operator analysis.
It is heuristic to observe that the last factor in Eq. (3.1) comes from the part
p1 in H, and it only induces a phase in the solution, therefore it would not change
the convergence or divergence of the square integral, i. e., the selfadjointness of
p 2 + x pm + pmx is exactly the same as x pm + pmx, and the latter one turns out
to be the same as p x m + xmp.
In other words, unlike the p2 in p2 + p xm + xmpr the p2 in
p2 + xpw will not change the properties of selfadjointness.
32
3.2 The Application of Boundary Conditions and SelfAdjoint Extensions at
Regular Points
Examples:
(a) A  p = 1 d/dx, with Q = [b, a]
py/Â±=Â±iyrÂ± , V4 = exp (+ x).
Thus, Â«+ = Â«. = 1, apply theorem 3 to this case, we have
fi= C]\f/++ c2Wf chc2e C
o = (/,,/,) = ( i ih/dx, ft)  (ft, dft/dx)  i [ft,ft] I*
= i Ift(Wft"(W ftto)ft"(fl)].
Set f\(b)/fi(a) = 2 ; we have 2 z* = 1, so z = exp(i0), 0 e 9^ For selfadjoint D(M) =
[^Cx): (
V*(W /i(fe)  yKa)fÃ(a) = 0
VKfe)/ yKa) = exp (iff) (3.2)
let us look at the eigenfunctions of p :
m = A y/xr
xpi ~ exp (z'Ax)
33
Vi(b)/ v^(fl) = exp (i'A( b  a))
y/x has to satisfy (3.2) to be in D(M); so we get
A( b  a) = 6+ 2m , n = 0,11, Â±2,...
Ã = (d+2m )/(ba).
The case of 6 = 0 is what is usually considered in quantum mechanics, and is
called the periodic boundary condition.
(b) H = p2 + x, with Ã2 = [0, + Â°o)
As we already discussed in (d) of Section 3.1.1, n+ = n. = 1 for Q = [0, + <*>).
Therefore*
0 = (Ml) = (p2/i + M/i)  v 2/i + xfo = (v 2h> /i)  (h,p2h)
=  (/i h /i fl) i o+~=M(0)  /i(0)/>).
So
fi(0)//1(0)=[/1(0)//1(0)J = tan6>
0â‚¬ 91,
D(M) = [!//(*): ( v^,/i) = 0 ], so the boundary condition at x = 0 is
i//(O)cos0  y/(O)sin0 = 0
(3.3)
34
In fact, at any regular point, the form is the same.
Consider a particle with 1/2 unit mass moving vertically in the earth's
gravitational field and set x = 0 at the surface of the earth, Q = [0, + Â°Â°). Then its
Hamiltonian is given by
H = p2 + mgx = p2 + x, by setting g = 2.
It is interesting to note that this system has a natural selfadjoint extension
set by y(0) = 0. That is the case of q = 0 in the above boundary condition (3.3).
Additionally consider a physical system of an electron in a uniform
electric field E applied in the + x direction. The form of the Hamiltonian is then
H = p2 + x with Ã2 = (  oÂ», + oÂ»). For such a system, no special boundary
condition is needed since n+ = n. = 0.
3.3 The Application of Boundary Conditions and SelfAdjoint Extensions at
Singular Points
In this section, we will look at the effect of an attractive central potential.
We discussed in the classical point of view that there is no trouble for systems
with nonrelativistic Coulomb potentials, since they have a full time evolution.
Here we will see that this holds because they are selfadjoint. We will also find
selfadjoint extensions for the superattractive potentials [V(r) = A/râ€, n> 2].
After separating the angular part from the radial part, we have
Hr = d 2/dr2 + 1(1 + l)/r 2 + V(r)
which acts on u(r) with the requirement that^w(r)p dr must converge.
35
(i) V(r) = A/r, A > O
Hr+ uÂ± = Â± i uÂ±, uÂ± + (Â±i + A/r  / (/ + 1 )/r 2)wÂ± = O
becomes, at small r,
wÂ± + (A/r  / (/ + l)/r2)uÂ± = 0
uÂ± ~ VT ZÂ± (2/ + d(2ÃAr) ~ VT (lÃÃrf(2Ã +1}.
Thus, with / > 0, nÂ±, o+ = 1.
//
At large r, uÂ± Â± iuÂ± = 0
and its is not hard to find that
"+, + 00=1
Therefore, (n+, n.) = (0,0) for H with a Coulomb potential.
(ii) V(r) = A/r2
uÂ± + (Â±2 +A/r 2 / (/ + l)/r2)uÂ± = 0.
At small r, the eigenfunction ue and uÂ± have the same form:
36
//
A  / (/ + 1)
+ T Â«Â±
= 0
uÂ±,uE~rP, p = 1/2 Â± V 1/4  (A  / (/ + 1))
For an swave (/ = 0) with A > 1/4 or A /(/ t1) > 1 /4, we have
uÂ±, ~ r 1/2sin (A'ln r), or r^^osiA'ln r)
where A' = [A / (/ + 1) 1/4]1/2. Then nÂ± 0* = 2. With nÂ±>+00 = l, we get
(n+, n.) = (1,1).
Now let us construct selfadjoint extensions: at small r,
fi = ci r1/2cos(A'ln r) + C2r 1/2sin(A'ln r).
Using ( o* [0 V*  0^1/ and noting that ( , ) is a bilinear form on
D(H+)xD(H+), and(/i ) = (h,g j, we have
Thus,
(r1/2sin(A'ln r),r ^sinfA'ln r) )o* = 0
(r 1/2C0S(A'ln r),r 1/2COs(A'ln r))jr = 0
(r1/2cos(A'ln r ), r ^sinfA'ln r )
0 = (/i,/i) = (cic2  cic2â€˜)A cic2= real.
Consequently c2/ci is also real. Set cj/ci = tan 8, where 6 e 9Ã; then
37
fi ~ r1/2cos(A'ln r  6)
The eigenfunctions have the same form at small r, i. e.,
ue = Cev1/2cos(A'ln r  6)
in order to satisfy (Â«Â£,/i ) = 0. In Ref. 4, the author found the dependence of
eigenenergy on the choice of 6. Because of 6, we have a oneparameter family of
selfadjoint extensions.
Further, D(M) = [ u(r): ( u, /i) = 0 ], and therefore the boundary condition
at r = 0 is given by
lim
r Â» 0*
u '(r)r1/2cos(A'ln r  6)
u(r) Â¿(r1/2cos(A'ln r  6))
dr
= 0
(hi) V{r) = A/r", n >2,
at small r,
Ur +(Â£ +A/r"  /(/ +l)/r2)wE = 0.
Ur +(A/rn)uE = 0
uE ~ VfZi/(â€ž+i)=Â¿&r(â€2)/2
Ln2
Using the Bessel asymptotic forms, we get
ue ~ r"/4sin(yr(â€'2)/2)
or
38
rn/4 cos(yr(Â«2)/2)
where y= 2ÃX /(Â« 2). uÂ± have the same form, so nÂ±t 0* = 2, (Â«+, n.) = (1,1).
The boundary condition is similar to (ii)
h  ci r"/4 sin(yr (n _2)/2 ) + C2rn/i cos(yr'2)/2)
using
(râ€/4 sin(yr _2)/2 ), r"/4 cos(/r(n 2>/2 )bâ€˜ = A1/2
Thus,
(/1, /1) = 0 gives C2/ci=tan6, 0e SR
fi ~ r"/4 sin(yrâ€˜(â€_2)/2 + 0)
ue = Ce r"/4 sin(yr
D(M) = [ Â«(r): (w, /1) = 0 ],
gives the requirement on u(r) at r > 0
lim
r â€”> 0*
u \r)r n/4 sin(yr 2)/2 + 0))  u(r) Â¿(râ€/4 sin(yr
dr
= 0
3.4. Conclusion
By calculating the deficiency indices for several representative examples of
Hermitian Hamiltonians, we have analyzed the possibilities in each case of
extending the operator to a selfadjoint one. In so doing we have confirmed the
39
connection proposed in the previous chapter that relates possible extensions to
associated characteristics in the solutions of the classical equations of motion.
The purpose of this chapter has been twofold: on the one hand, by demonstrating
that anomalies in the classical solutions to a dynamical system are reflected in
anomalies of the quantum Hamiltonian, certain technical issues ( such as
deficiency indices, etc.) are brought into the realm of everyday experience. On
the other hand, the intimate connection between classical and quantum
properties should enable one to examine a given system at a classical level in
order to assess what problems, if any, are expected to arise at the quantum level.
40
Table 1 Summary of classical and quantum highlights associated with several model problems Each model has a label, a classical Hamiltonian, typical
solution trajectories, nature of those solutions, character of quantum Hamiltonian, spectral properties, and. In some cases, related esamples as well T he
solid curve in the figure portionÂ» represents a typical trajectory or part of a trajectory in the case of a periodic orbit The doited curve denotes an
alternative typical trajectory, and the dashed curve denotes a periodic extension oÃ the basic orbit In d, the figure illustrates two possibly distinct periodic
extensions, h is omitted because it is a related example of d.
Example
Label
Classical
Hamiltonian
H
Qualitative Graph
t(q) of equations
of motion
Nature of
Classical
solutions
Selfadjoint
Quantum
Hamiltonian
Spectral
Properties
Related Examples
m = 1,2,3,
a
pâ€™ + Â«4
t
global
unique
discrete
pâ€™ +
â€”
t
pâ€™ + Â«S
t
â€”
periodic
one parameter
family of
solution (one
boundary
condition)
discrete
p5?5
pâ€™ Â± ?,m+>
=â– =
/ * y
c
2p?5
t
Q
partially
complex
nonexistent
none
P 1 , m = odd
^
r
d
P5  14
 
t
'
W
periodic
two parameter
family of
solution (two
boundary
conditions)
discrete
P5  7,m , m > 2
p5 + 2p7m , m > 2
t
pâ€™Â«â€™
i
global
unique
continuous
PJ + 2pÂ«
A
5
41
1 able I (Continued )
Kxample
label
Classical
Hamiltonian
//
Qualitative Graph
Ã(7) of equations
of motion
Nature of
Classical
solutions
Selfadjoint.
Quantum
Hamiltonian
Spec t ral
Properties
Related Pxarnples
rn â€” 1.2 3.
/
2,.,;
global
unique
continuous
/'7>m . rn > 1 . ru â€” even
9
2 v/l
A
t
t
/ â€” ?
e*
part Â¡ally
complex
nonexistent
none
2;i/?nâ€˜ . rn = odd
\
ir/i + pâ€™
^
\
piece wise
continuous
one parameter
family of
solution
continuous
P5 + 2p/irâ€
j
P?  * + ^
A > 0
Â£
1
AA,
i
<â€”' '
i i
global
unique
discrete
t
pi _ A + ÃœÃ+U
/ r r" ' r *
Ã‰
A
Aâ€”.
>
x*
x tr
periodic
one parameter
family of
solution.
discrete
42
Table I. (Continued.)
Example
Label
Classical
Hamiltonian
H
Qualitative Graph
t(q) of equations
of motion
Nature of
Classical
solutions
Selfadjoint
Quantum
Hamiltonian
Spectral
Properties
Related Examples
m = 1,2,3,
/
2 PI
i
\
\
r'
global
unique
continuous
m
P5 + V
:
global
unique
continuous
Fig. 1 Classical trajectories for the simple Hamiltonian H=p in three separate coordinate domains: (a) â€” oc
(b) 0
PART II
OPERATOR ANALYSIS
AND
FUNCTIONAL INTEGRAL REPRESENTATION
OF
NONRENORMALIZABLE MULTICOMPONENT ULTRALOCAL MODELS
CHAPTER 4
INTRODUCTION
As we know, the features of infinitely many degrees of freedom and
noncompact invariance groups have made the structure of quantum field
theory very complex. So seeking for the proper formulation of problems in
quantum field theory has been a difficult yet exciting endeavor in our
research. Even though conventional perturbation theory5'6, which is based on
a free field formulation, has proved successful in solving some problems, e.g.,
quantum electrodynamics (QED), we must ascertain whether the free field can
be generally used as the basis for a perturbation expansion7. One of the results
that arose from the traditional perturbation analysis based on free fields is the
appearance of nonrenormalizable interactions which some physicists regard
as hopeless. Therefore the structure of nonrenormalizable models has been
largely ignored over the years. Twenty years ago, the pseudofree theory was
proposed by Klauder7'8 in the study of ultralocal field models to extend the
usefulness of perturbation theory. An argument based on asymptotic
convergence suggests that the free theory is connected with continuous
perturbations while the pseudofree theory is related to discontinuous
perturbations, which have much to do with nonrenormalizable interactions.
At about the same time, a functional and operator approach to singleÂ¬
component ultralocal field models was developed through general
nonperturbative and cutoff free arguments9'10. There Klauder gave an
44
45
alternative quantum theory of such models, which does not fit into the
canonical framework. He also showed that as any interaction is turned off.
after it was once introduced, the theory will not pass continuously to the free
theory, but rather to a distinctly different pseudofree theory. Clearly,
conventional perturbation theory could not be applied to such a model.
The ultralocal model is obtained from covariant model by dropping the
spacegradient term. Since distinct spatial points there characterize
independent fields for all times, it unavoidably results in a
nonrenormalizable situation. We are interested in this model because it is
solvable by nonperturbative techniques and may give us some insight into
the structure of nonrenormalizable fields.
In chapter 5, we will show that just like nonrenormalizable relativistic
quantum field theories, on one hand they exhibit an infinite number of
distinct divergences when treated perturbatively, while on the other hand
they frequently reduce to (generalized) free fields when defined as the
continuum limit of conventional latticespace formulation11, ultralocal
models are specialized nonrenormalizable theories that also exhibit infinitely
many perturbative divergences and an analogous (generalized) freefield
behavior when defined through a conventional lattice limit12. However, the
characterization of infinitely divisible distributions13 allows ultralocal models
alternative operator solutions9'10 (also Chapter 6), which lead to a nontrivial
(nonGaussian) solution on the basis of operator methods. The validity of
this nontrivial solution is supported by the fact that the nontrivial quantum
solution reduces to the correct classical theory in a suitable limit as h â€”> 0; the
trivial (Gaussian) solution has no such correct classical limit (Chapter 7)12.
Recently, it has been found how to obtain the same nontrivial results
offered by operator techniques through the continuum limit of a
46
nonconventional latticespace formulation14. The key ingredient in the
latticespace formulation that leads to the correct behavior is the presence of
an additional nonclasssical, local potential besides the normally expected
terms.
In chapter 6, we will construct the operator theory of 0(N)invariant
multicomponent nonrenormalizable ultralocal models, where N < <*>. It has
been surprisingly found that the singular, nonclassical term in the
Hamiltonian which showed up in the onecomponent ultralocal fields can be
made to disappear15, when N, the number of field components, satisfies N>4.
Nevertheless, a similar singular, nonclassical term still appears in the
regularized pathintegral formulation16 that leads to the same nontrivial
quantum results for O(N) invariant multicomponent scalar fields (Chapter
8). Thus, for any N, the number of field components, the new path integral
formulation involving the singular, nonclassical term replaces the standard
lattice approach which invariably leads to a Gaussian theory regardless of any
nonlinear interactions, and supports the concept of a pseudofree theory.
One advantage of deriving the operator solutions by a latticespace
formulation is the clear focus the latter approach places on the differences
from traditional approaches needed to lead to nontriviality. These differences
for ultralocal models suggest plausible modifications in the latticespace
formulation of relativistic nonrenormalizable modes that may lead to
nontriviality for Ncomponent models such as n > 5 (and possibly n = 4),
for N > 1.
In my future research, I hope to extend analogous reformulations to
covariant quantum fields, the possible relevance of which has already been
noted23. The general argument is partially based on the realization that the
47
classical theory of a typical nonrenormalizable interaction exists and is
nontrivial24.
CHAPTER 5
CLASSICAL ULTRALOCAL MODEL AND THE STANDARD
LATTICE APPROACH
The classical Hamiltonian of an ultralocal scalar field is expressed as
Hci = j J1ji2(x) + lm2(p2(x) + Vi[
where n, cp denote the classical momentum and field respectively, and Vi[cp]
(= Vi[ 
configuration space of arbitrary dimension, xe9?n"\ This model evidently
differs from a conventional relativistic field theory by the absence of the term
The classical canonical equations of motion appropriate to (5.1)
become
iWx)]
(p(x,t)=JHci_ = 7I(x,t),
5rc(x,t)
ir(x,t) =  5Hcl =  m2(p(x,t)  Vj[(p(x,t)], (5.2)
5
Cp(x,t) = m2(p(x,t) Vj[cp(x,t)].
Unlike conventional canonical field quantization, the quantum theory
of ultralocal fields does not follow from standard canonical commutation
relations, etc., whenever a nonlinear interaction exists. In particular, we do
not have an equation such as (5.2) for local quantum operators (see Chap. 6).
48
49
Nevertheless, it is instructive to first examine these models from a
conventional lattice limit viewpoint.
Let us take a look at the result from a standard functional integral
approach (which is based on the standard canonical quantization) where the
vacuumtovacuum transition amplitude is formally given by 6:
ZQ] = ^ 'DQexpii
cf x J(x,t)(x,t) + Ã4> (x,t)  L (m^
2 2
ie) 2(x,t)  g
I
/'
4
where we have chosen VÂ¡ (O) = gO as an example. Using a latticespace
regularization in the space direction (but not in the time direction) we obtain
I
Z[J] = 9\i lim^o I (FI exp i dt Ik a
I
Jk(t)4>k(t) + LÃ³k (t) 1 (m2  ie) 4>^(t)  gOif (t)
2 2 .
J,
= limfl^o [I j 2>* expji j dt a
I
J k(t)0 (t) + iÃ³ (t)  L (m2  ie) 2(t)  g04(t)
2 2
where k labels points in the spatial lattice and a is the volume of the unit cell
in the spatial lattice. As we now show, the result for such an interacting
model leads in the continuum limit to the analog of a generalized free field.
From the preceding equation, using u = O Va, go =g/a, and < â€¢ > as an average
in the complex distribution, we have
Z[J] = Vi hm^o IT
k
J k(t)u(t)VÃ¡ + lÃº2(t)
2
50
I
limado II < exp{i I dt J k(t)u(t)Va } >
= lim^oIT {l [ I J k(t)u(t) dt ]2> + [ I J k(t)u(t) dt ]4 > + â€¢ â€¢ â€¢}
4!
/
= exp {1/2 I d x dt dt' J(x, t) J(x, t') < u(t) u(t') > }.
(5.3)
Evidently (5.3) is a Gaussian result in which (assuming 0
J,
< u(t) u(t') > = ti I 'Du u(t) u(t') exp dt
I
lÃº2(t) 1 (m2  ie) u2(t) gu4(t)]
= < O IQ exp(  i I ttâ€™ IH )Q I 0 >
= Â£<0 I Q I n > e < n I Q I 0 >
â€™y Pn q  i I tt' I mn
n 2mn
(5.4)
where mn, n=l, 2, 3, denote the eigenvalues of H,
Pn = I < 0 I Q I n > I 2.
2mn
H = 1/2 (P2 + m2^ ) +gQ4  const., and the constant is chosen so that H10 >=0.
It is easy to verify that ^ pn = 1, and since < 01QH4Q 10 > < it follows that
n
oo
^ pnm^ < oo. Thus we have
Z[J] = exp {1 /4J d3xdtdt'J(x,t)J(x,tâ€™)X (pn/mn) e *iltt'lmn }
51
= i! exp {
n
d3 x dt dt' J(x, t) J(x, t') e â€˜11 ttâ€™1 mn }.
(5.5)
The ultralocal free field corresponds to g= g=0, in which case mn = mn ,
Pi = 1/ Pn = 0 (n*l) in (5.4), so that
< u(t) u(t') > =_Leiltflm .
2m
Then (5.3) gives
Zf[J] = exp {
d3 x dt dt' J(x, t) J(x, t') e â€˜11 t_t'1 m }
= <0 I Texpfil d4xJ(x,t)Op (x,t)} I 0 >. (5.6)
Observe that the ultralocal free field operator Op (x,t) satisfies
â– â– m m
Op (x,t) + m2Op (x,t) = 0.
Comparing (5.5) and Eq. (5.6), we get
ZQ] = IT < 0 1 Texp {i
d^ J(x,t)0â„¢n(x,t)} I 0 >
= < 0 I Texp {i d^ J(x,t) X
0>
= < O I Texp {i I d'Sc J(x,t) 0(x,t)} I 0 >,
(5.7)
where (x,t) =X F^fot). 0?ln(x,t) are ultralocal free field operators with
n
mass mn , n = 1,2,3â€¢ â– â– ,which satisfy Op "(x,t) + nrÂ¿Op^fot) = 0 for each n.
From (5.7) we see that our regularized interacting model has led in the
continuum limit to an ultralocal generalized free field, a natural analog of the
relativistic generalized free field17. As a consequence of
[0(x,t), [0(y,t), 0(z,t)] ] = 0, which holds for a generalized free field under our
present conditions, it is clear that the field operator O of an interaction like
4
Vi (O) = g with g>0 can not satisfy this commutation equation. Obviously
this (generalized) freefield behavior is limited neither to g
replaced by other local powers), or to the spacetime dimension n=4. This fact
indicates some sort of failure of the conventional formulation of canonical
field quantization for these models. Moreover, with the help of coherent state
techniques18'19 we find that the classical limit of an ultralocal generalized free
field does not limit as (h Â»0) to a classical field that satisfies the classical
nonlinear canonical Eq.(1.2); instead, the classical limit of
n n
CHAPTER 6
OPERATOR ANALYSIS OF MULTICOMPONENT
ULTRALOCAL MODELS
The quantum theory of ultralocal scalar fields had been discussed
extensively by Klauder9'10 over two decades ago. The employment of probability
theory and Hilbert space methods with an emphasis on infinitely divisible
distributions and coherent states techniques, respectively, enables us to give a
proper quantization of these models, which otherwise are meaningless within
the conventional canonical formulation of quantum field theory (see chap. 5).
An operator solution of multicomponent, nonrenormalizable,
ultralocal quantum field models is developed here along lines presented
earlier for singlecomponent models. In Â§6.2, we will show that the
additional, nonclassical, repulsive potential that is always present in the
solution of the singlecomponent case becomes indefinite and may even
vanish in the multicomponent case. The disappearance of that nonclassical
and singular potential does not mean a return to standard field theory. The
operator solution of multicomponent ultralocal fields remains
noncanonical. In Â§6.3, we will show that nontrivial, i.e., nongaussian, results
hold for any number N of components, and suitable nontrivial behavior
persists even in the infinitecomponent ( N=Â°Â° ) case as well.
53
54
6.1 Operator Analysis of SingleComponent Ultralocal Models
Let us briefly summarize the operator analysis of singlecomponent
ultralocal models9'10. Assume that the field operator O(x) becomes self
adjoint after smearing with a real test function f(x) at sharp time. Since
distinct spatial points characterize independent fields for all time, we may
write the expectation functional as
(6.1)
Where in the last step, we have used the result of Levy's canonical
representation theorem for the infinitely divisible characteristic functions13,
and have eliminated a possible contribution of the Gaussian component,
which applies to the free field. The real, even function c(A) is called the
"model function".
An operator realization for the field O(x) is straightforward. Let
A+(x, X) and A(x, X) denote conventional, irreducible Fock representation
operators for which 10 > is the unique vacuum, A(x, A,) 10 > = 0, for all
xe 9ln \ Xe 9L The only nonvanishing commutator is given by
(6.2)
Introduce the translated Fock operators
55
B(x,X) = A(x, X) + c(X), B+(x,W =A+(x,W + c(X), (6.3)
Obviously, the operators B+(x, X) and B(x, A.) follow the same commutation
relation (6.2). Then the operator realization for the field O(x) is given by
The correctness of this expression relies on the fact that
â€¢I
< 0 I exp{ i I dxO(x)f(x)} I 0 >
=< 0 I exp {i
=< 0 I: exp {
i j dxj dA. B+(x,
j dxj dX. B+(x,
X) Xf(x)B(x, X)} I 0 >
*)(eW*>l)B(x,X)}:l 0>
= exp { j dxj dA. [ 1  e^M] c2(X.)}
as required by (6.1).
The Hamiltonian operator is constructed from the creation and
annihilation operators and is given by
H = J dxj dX. B+(x, X) h(d/dX, X) B(x, A.)
56
= j dxj dX A+(x,
X) h(B/3X, X) A(x, X).
(6.5)
Where h(3/3X, X) = btdi2/3X2+ V(X), which is a selfadjoint operator in the X
variable alone. It is necessary that h(3/3X, X) > 0 in order that H > 0 and that
I 0 > be a unique ground state. Equality of the two expressions in (6.5) requires
h(3/3X, X) c(X) = 0, implying that c(X) e L2 in order for 10 > to be unique. This
relation also determines V(X) as V(X) = b2 c"(K)/c(k). Assuming that
dXX2 c2(X) < Â©o, so that <0 I02(f) I0><Â°o, where O(f) = I dx
I
I
â– I
together with the condition I dX c2(X) = we are led to choose
c(W=l^exp{^mx2y(4
(6.6)
where y, called the "singularity parameter", satisfies l/2
have (pk =  ih B/BX )
h(3/3X, X) =  b2^ + Y(Y+1)^2 + m(Y. 1/2)h + jnn2X2 + Vi(X)
2 BX2 2X2 2
= }:Px2 +^^ + m(Yl/2)^ + iin2X2 + VI(X), (6.7)
2 2X 2
Vi(X) = y ( y" + y'2) + ( mftX + yh2/\ ) y'. (6.7b)
This equation determines c(X) for any given interaction potential VÂ¡(X), at
least in principle. Notice that in addition to the free term â€” p^2 + ^m2X2 and
2 2
57
the interaction term Vi(A.), there appears a nonvanishing, positive, singular
and nonclassical potential y{y+\)h2/2X . It is important to note that this
additional potential makes the pathintegral formulation of ultralocal fields
totally different than that of standard quantum field theory14.
The definition of renormalized local powers of the field follows from
the operator product expansion
O(x) O(y) = 5(xy) di B+(x, X) X2 B(x, X) + :
which suggests the definition
I
dX B+ (x, X) X2 B(x, AO = Z O2 (x), Z'1 = 5 (0) (6.8)
or more generally,
Ork(x) = j dX B+(x, X) Xk B(x, X) = 1[Z 0(x)]k, k = 1,2,3, â€¢ â– â– (6.9)
For k > 1, these expressions are local operators, i.e., become operators when
dA. B+(x, X) 1 B(x, A.), and
X
I dA. B+(x, X) B(x, X) = O,1 (x), then we can extend (6.9) for renormalized
J X
k
negative powers of the field. But we should note that for k < 0, r(x) are not
local operators.
l,
smeared by a test function. For k < 0, let Oâ€™ (x) =
sZ1
58
Corresponding to (6.7), the Hamiltonian may be expressed by
renormalized fields as
H = j jirÃÃx) + Im2
2 â€˜ 2 92 0
where nr = Or+ y(y+l)/r Â®r + m(2y\)h Â®r Obviously it means that nr
neither fits into the canonical framework! flr = Or ) nor fulfills the standard
canonical commutation relation [Or(x), nr(y)] = i hh{x  y). We should also
notice that although Â®r ( = O = i [ O, H ] /h = ih J dX B+(x, X) d/dX B(x, X) ) is
not a local operator due to the assumption regarding c(X), neither are
â€¢220 2
Or,Or ,0>r local operators by themselves alone; only the combination Fir is a
welldefined local operator. These are major differences from standard
quantum field theory.
The Heisenberg field operator is given by
0(x,t) = eiHt/fc O(x) ein*/**
â– /
â– I
dX B+(x, X) e,ht//'Xe'iht/fi B(x, X)
dX B+(x, X) X(t) B(x, X)
(6.11)
which is well defined. The timeordered truncated npoint vacuum
expectation values are given by
< 01T [0(Xl,ti) 0(x2,t2) â€¢ â€¢ â– Â®(xn/tn)] 10 >T
59
= 5(xrx2) 5(x2x3) â€¢ â€¢
5(xnixn)
 dXc^TtMtOMt^.Xan)] c(X).
(6.12)
For ultralocal pseudofree fields ( defined when the interaction
potential Vi(A.) vanishes ), we have the model function
ca)=M'Y exp { mX2/2h }, and the expectation functional
E[f] = exp {
â€¢M
dX
1  tos [ Xf (x) ]
W*
exp
(6.13)
which is obviously not a Gaussian solution such as for ultralocal free fields.
In Â§6.2, the operator analysis of finitecomponent ultralocal models is
presented. There we will see how an indefinite (positive, negative or
vanishing), singular, and nonclassical potential affects the operator solutions.
In Â§6.3, the expectation functional of infinitecomponent ultralocal
fields is discussed. Even in this case the solution of any interacting theory
does not reduce to that of the free theory in the limit of vanishing nonlinear
interaction and again supports the concept of a pseudofree theory7'8.
60
6.2 Operator Analysis of FiniteComponent Ultralocal Fields
Following the pattern of the singlecomponent case, the field operator
and the Hamiltonian of N component ultralocal fields are defined by
d>(x) =
I
dX B+(x, X) X B(x, X)
(6.14)
and
dX B+(x, X) h(Vx, X) B(x, X)
dX A+(x, X) h(V^, X) A(x, X)
(6.15)
where h(Vx, X) =  + V(A), X svr2. Notice that here the Ncomponent
ultralocal models under consideration have O(N) symmetry. The
commutation relation becomes
[a(x, X), A+(x', X')} = 5(xx') b(XX')
(6.16)
and the unique ground state satisfies A(x, X) 10 > = 0. The operator B(x, X) is
related to A(x, X) by
B(x, A.) = A(x, X) + c(X).
(6.17)
The renormalized local powers of the field are given by
61
â– I
^ri,...ik(x) S dX BT(x, X) XÂ¡, â€¢ Xik B(x, X), ii, â€¢ â€¢ â€¢ ,ik = 1, 2,3, â€¢ â€¢ â– N
Occasionally, we need to use the renormalized negative powers of the field
even though they are not local operators. Take a singlecomponent case for an
example:
Orf(x) =
I
dXB+(x,X)X,kB(x,X) = MZ Oi(x)]1
Zj
i = 1,2 â€¢ â– â€¢ N,
(6.18)
which can be extended to k < 0, as long as we define
Oj1 (x) =Z? I dXB+(x,X)â€”B(x,X) and dXB+(x,X)JB(x,X) = ch^x).
] Xi J Xi
From the requirement that h(V^, X) c(X) = 0, we have
1 ? 2
V(X) =Hi Vxc(k)/c(k). The real, even model function c(X) becomes
c(X) = â€” exp   ^LmX2  y(X)
(6.19)
with N/2 < T < N/2 +
dNX c2(X) = oo and
I
I
1 which is determined by the conditions
dNX X2 c2(X) < oo.
Next let us find out how the operator h(V^, X) appears. From (6.19), it
follows that
V(X) = lfi2Vxc(X)
2 c(X)
_ fi2 V" d2
2 c(X) i=i a^2
c(X)
(6.20)
= r(r+2 ~N)â€” + mh(T N/2) + Â±m2X2 + Vi(X),
2X2 2
where Vi(/.) = 1/z2 ( y" + y'2 ) + y' { mhX + [ T (Nl)/2 ] h2/X }, which
corresponds to the interaction. Therefore
h(VÂ¡, X) =  ^2VÃ + V(X)
2
=  h2vl + r(r+2 ' N)h â– +mh(r N/2) + Un2X2 + Vi(X). (6.21)
2 IX2 2
This base Hamiltonian of multicomponent ultralocal fields is similar to that
of singlecomponent ultralocal fields (6.7); but a surprising difference between
the two equations is that unlike the nonvanishing, positive, singular and
nonclassical potential y[y+\)h2/2X2 appearing in (6.7), T(r+2  N)^2/2^.2 is not
always positive and moreover it may vanish. These properties follow since
N/2 < T < N/2 + 1, i.e., 0 < T  N/2 < 1 and therefore
2  N/2 < r+2  N = 2 + ( T  N/2)  N/2 < 3  N/2.
Summarizing, T+2N>0 for N<4; r+2N<0 for N>6; and T+2N is
indefinite, when 4
even equal to zero. As examples of vanishing T(r+2  N)/r/2X we have N=4
and T=2, or N=5 and T=3.
It is worth mentioning that the disappearance of T(r+2  N)Ã±2/2X2 does
not mean a return to standard (canonical) field theory or standard path
63
integral formulation; even in this case it can be shown that a similar nonÂ¬
vanishing, singular, nonclassical potential arises in the regularized path
integral formulation (Chapter 8).
It is worthwhile to discuss further the Hamiltonian which according to
(6.21), is given by
H =
= j Â±nr(x) + im2Or(x) + Vi[Or(x)] dx.
(6.22)
2 ^*2 â€” 2 â€” 0
Here nr(x) = Or(x) + r(r+2  N)/Â¡21 Or(x) I + m/i(2rN) lOr(x)l . Notice that
j d?, B+(x, X) (Ã±2 d2/dX,2 )B(x, X) ,
i=l, 2, N, are not local operators,
â€” o â€” 2
neither are On(x), IOr(x)l or IOr(x)l , but somewhat surprisingly
N . 2
^ On (x) = Or(x) is a welldefined operator for N=4 and T=2 and
i=l
N . 2 â€” 0 ^*2 â€” 0
2_, On (x) + mÂ£ IOr I =Or(x) + m/z I
i=l
*2 =*2
and T=2, we have nr(x) = Or(x), which in the present case is a local operator,
but nr(x) = Or(x) involves local forms rather than local operators due to the ill
defined On(x).
Summarizing, the canonical equation nr(x) = Or(x) and the standard
canonical commutation relation [On(x), ft^fy)] = i^5jj5(x  y) do not hold for
the multicomponent ultralocal fields, just as for the singlecomponent
ultralocal fields, irrespect of whether the singular potential T(T+2  N)Ã±2/2X
â€” 2
[~ I Or(x) I ] is present or not.
Analogous to the singlecomponent case, the Heisenberg field operator
is given by
64
â– /
â– Ã
dX B+(x, X) eiht/^Xe_iht/fi B(x, X)
dX B+(x, X) X(t) B(x, X)
(6.23)
which is well defined. It follows that the timeordered, truncated npoint
function reads
< 0 I T [Oi/x^ti) <*>i2(X2,t2) â€¢ â– â€¢ ^(XnA)] 10 >T
= 5(xrx2) 5(x2x3) â– â€¢ â€¢ 5(xn.rxn) dX c(X) TlXJt!) Xj2(t2) â€¢ â€¢ . Xin(tn>] c(X).
(6.24)
65
6.3 Operator Analysis of InfiniteComponent Ultralocal Fields
The expectation functional of finitecomponent fields is
E[f] = < 0 I exp
dx 3>(x)f(x) I 0 >
= exp { g
dX [ 1  e^'f(x)] C2(X)}.
(6.25)
Here we have introduced g , a scale factor which cannot be determined on
general grounds but rather represents the only arbitrary renormalization scale
involved in the operator construction. The possibility of its existence lies in
the fact that two model functions differing by a constant factor lead to the
same differential operator h and thus to the same Hamiltonian H.
An operator realization of the infinitecomponent field requires us to
give a proper measure which is well defined. In doing so, notice that we can
absorb the model function c(X) into the measure so that we have the new
measure dp(X) = g c2(X) ndXj. Let us redefine the commutator
A(x, X), A+(x', X')\ = 5(xx') 5P(X; X'),
(6.26)
where 5p(X; X') is related to the measure p by J dp(Xâ€™) f(Xâ€™)5p(X; X') = f(X). The
operator B and the infinitecomponent field are redefined as
66
B(x, X) = A(x, X) + 1,
(6.27)
O(x) = j dp(X) B+(x, X) X B(x, X).
(6.28)
Then we immediately recognize that (6.25) stays the same. The renormalized
local powers of the field and the Hamiltonian are given analogously by
ik(x) s j dp(X) B+(x, X) Xu â€¢ X[k B(x, X), ii, â€¢ â€¢ â€¢ ,ik = 1, 2,3, â€¢
â€¢ â– N, (6.29)
and
H = j dxj dp(X) B+(x, X) h(Vh X) B(x, X)
= J dxj dp(X) A+(x, X) h(V^, X) A(x, X),
(6.30)
with the requirement of h(V^, A.)l = 0. The Heisenberg field operator is
given by
0(x,t) = eiHt/ft O(x)
I dp(X) B+(x, X) eiht/^eiht/* B(x, X)
l dp(X) B+(x, X) X(t) B(x, X).
(6.31)
The timeordered, truncated npoint function reads
67
< O I T [Oi,(Xi,ti) i2(X2,t2) â€¢ â€¢ â€¢ O^Xrvtn)] I 0 >T
= 6(xiX2) 5(x2x3) â€¢ â– â€¢ 8(xn_rXn)
I
dp(WTI^I(t1)Aia(t2)..Xi.(tn)M.
(6.32)
It is worth mentioning that the above formulation for the infinite
component case is suitable for the finite component case as well.
Next we try to obtain the characteristic functional of infinite
component fields as the limit of finitecomponent ones. Take the general
form of c(X) = X Fexp   ^mA.2  y(A.)J in the finite case, then we have
E[f] = expj gj dxj dX [ 1  1 exp [  lmA.2  2y(X) ] (6.33)
In order for this limit to exist as we need to scale several parameters,
namely y=yN/ m=m>j and to choose a suitable factor g=gN Following the
Ref. 22, suppressing the integration over x, let us consider
68
Ã
where  dr rn ev = SL has been used. If we introduce the Fourier transform
yi+l
pair: e' 2YN^) = j d^ 1\n(!;) e'^Â¿, h^) = dAZ e'2YN(:>l) e*1^, L[f] can be
expressed as
lim
Nâ€”> <
â€”J dr râ„¢ J dX[l  e^'f ] exp   (^mN + r) A2 + iÂ£A" jh^C^) dÂ£,
The integration over A now involves simply Gaussian integration
U dx e"00^ +^â€˜x = (^)N/2 e?/4a  and leads to
lim
Nâ€”
_SN_ f dr rri / e N/2 [ 1  e?/ 4(mN/h + r  Â£)] hN(^) dt
(r1)! J0 \mN//z + r  Â£1
= lim
NÂ».
â€” J dr r^mN/r/j  i^/r + i)'N/2[ l  e'?/ 4(mN/ti + r  iÂ£)] hN(Â£) dE,
(rD! A
where 1 < 0 = TlN/2 < 0. Now we are ready to make the choice of y^, m^
and gN Assume that gN= g^'N/2(rl)!, m^= m/N and yxKA) = y (A/ÃÃ‘") which
suggests that hjsr(^) = N h(N^). Following a change of variables of we take
the limit by using lim^^^i 1  expJL(m//i  iÂ£)j,
and we get
L[f] = g I dr re expj ^(m/h  Â¡4) J [ 1  e?/ 4r] h(Â£) d^
Jo
69
= g j dr re expj'^ (m/fi)  2 y(J) [ 1  e?/ 4r]
â€¢/o
= g I do â€”2â€” exp( (m//z) o  2y(o)} [ 1  e of2/2], (6.35)
Jo (2o)e+2 1 1
where 1 < 0 < 0, and in the last step, we have substituted o = l/(2r).
We can also try in the following way to obtain the characteristic
functional of infinitecomponent fields as the limit of finitecomponent
ones. Take the general form of c(X) = X'rexp j  ^LmX2  y(X)J in the finite
case, then we have
E[f] = exp {
W
dp(A.) [ 1  e^â€™fW] }
= exp g
I dxI dX [ 1  e^^'^x)]â€”exp [ l*nX22y(X) ]/
J J x2r h I
1
(6.36)
In order for this limit to exist as Nâ€”>Â«, we need to scale several parameters,
namely y=y^, m=m^ and to choose a suitable factor g=gN Suppressing the
integration over x, let us consider
I
L[f] = dpN(W[le^fW]
(6.37)
I
2r
= gN I dX [ 1  e1^'f ] J exp j  fmNX2  2yN(X)
70
= lim
Nâ€”>oo gN
j dXâ€”â€”  exp  imN^.2 2yu(X) jj dÃÃ [ 1  cos Â®]. (6.38)
Where dQ= sinN'2 0 d0 df2'. By changing the variable 0 Â»0/N + k/2 and
taking N large, we have cos 0 =  sin (0/N) =  0/N and therefore
~ . ~ 2 N2 ~ 2
sinN2 0= cosN2 (0/N)  [ 1  1(0/N) ] Â« exp[  Â±{0/N) (N  2) ]. Hence we
may write
J dQ [ 1  e&f cos Q]=J d0 exp[  i02(N  2) ] [ 1  e~ iXf0]J dÂ£T
2k.
N2
j dn' { 1 exp[lf2X2/(N2)]}
= S{lexp[lf2X2/(N2)]}.
(6.39)
Where S denotes the spherical surface area in Ndimensions, N Â» 1, namely
S =
2 n
N2
N/2j dir.
Substituting (6.39) into (6.38), we have
L[f] =/i'mN_>00 gN J dX 1 exp j lmNX2 2yN(X) I S {1  exp[ lfV/(N  2)]}
J ^2rN + i \ Ã± J 2
= /^N^oogN j dXN y)/2SCxpjlmNNX2 2yN(fÃ‘" X)j {1 exp[lf2X2^L]}.
In the last step we have made a change of variables of Xâ€”>VÃ‘~ X', p = 2T N + 1.
71
Now we must choose yu, mN and gjsj. Assume that mÂ¡sj= m/N,
yN(X) = y (A./VÃ‘) and gN= N^'^/^g/S, where gis proportional to g in (6.35).
By taking the limit we obtain
(6.40)
where 1< p< 3. So the characteristic functional of infinitecomponent fields
becomes
= exp g
From (6.41), we see that a nontrivial, i.e., nonGaussian, result holds for
infinitecomponent fields, just as it does for the finitecomponent ones.
Notice that the scalings we have used here, such as mw= m/N and
yrA) = y (A./VÃ‘), are different from the standard ones. For example: for
4 ~*4
Vi = O , the standard scaling assumes (Vi)n = O /N, while the nonstandard
scaling employs mN= m/N and yrA) = y (A./VÃ‘) which gives
(Vi)rAl = VitX/VÃ‘T] = X4/N2 or equivalently (Vi)N[i>] = VitO/lbf] = 04/N2.
The nonstandard scaling admits a 1/N expansion relevant to the Poisson
distributed finiteN solution, while the standard scaling does not. Another
similar nonstandard scaling example was shown to hold in the independent
*2 *2
value models where mfo = m2/N, (Vi)n[0 ] = VjÃO /N] are also used22.
72
Judging from these examples it would appear that the standard scaling may
fail for certain nonrenormalized fields.
CHAPTER 7
THE CLASSICAL LIMIT OF ULTRALOCAL MODELS
As given in chapter 5, the classical Hamiltonian of an ultralocal scalar
field may expressed as
Hci = j J~"7C2(x) + lm2(p2(x) + Vi[
where xe SR0"1,7t,
the interaction potential. The classical canonical equations of motion
appropriate to (7.1) are
8rc(x,t)
7t(x,t) =   SHcl =  m2cp(x,t)  Vj[
5cp(x,t)
In fact, these formulas do not take into account a vestige of the quantum
theory that really is part of the classical action. Since the additional,
nonclassical, repulsive potential proportional to (field )'2 in (6.10) belongs in
73
74
the quantum Hamiltonian density, as Ã± Â»0 the coefficient of this term
vanishes save when tp(x) = 0. To account for this term we formally write
0(p'2(x,t) in the classical Hamiltonian density, and to respect this potential we
need to derive the equations of motion for (p(x,t) by means of a scale
transformation20, namely, using 8cp(x,t) = 5S(x,t)(p(x,t). This leads to a related
but alternative set of classical equations of motion (see Examples 1 and 2
below).
In the following, we will show that the alternative quantum theory of
ultralocal scalar fields described in Chapter 6 does indeed lead to the required
classical limit as h Â»0, thereby giving additional support to such an
alternative, nonGaussian solution.
7.1 Ultralocal Fields and Associated Coherent States
The proper quantum Hamiltonian of ultralocal fields given by (6.10)
has an evident connection with the classical Hamiltonian. In (6.10), the
subscript 'r' means the fields are renormalized, and instead of fl = O, we have
According to (6.4) and (6.5), the field operator O and Hamiltonian
operator are given by
B(x, X) = A(x, X) + c(X),
(7.3)
75
dX A+(x, X) h(â€”, X) A(x, XX
dX
dX B+(x, X) h (â€”, X) B(x, X), (7.4)
dX
with h(â€”, X) =  H2â€” + y{y+1)h2 + Lm2X2 + V^X)
M 2 dX2 2X2 2
= \ Px2 + + Â±m2X2 + V:(X) , (7.5)
2 2r 2
(PjL =. in A)
dX
Here we write the interaction potential as Vi(X) instead of Vi(X), since we
have used Vi as the classical interaction potential in (7.1). By using
exp(^Ht) B(x, X) exp(  Â¿Ht) = exp[  M h(â€”, X) ] B(x, X,) (7.6)
Ã± h h Â¿X
we can show that the Heisenberg field operator for any renormalized field
power is given by
OrG(x, t)= dX B+(x, X)exp[ M h(â€”, X) ] X6exp[  Â¿t h(â€”, X) ] B(x, X)
J * dx * ax
 dX B+(x, X) X6(t) B(x, X),
(7.7)
76
where XG(t) = exp[ 4 h(â€”, X) ] X6exp[  4 h(â€”, X) ] . Even though
* dX Ã± dX
[Or(x), nr(y)] * iÃ± 5(x  y), the variables X and p^ satisfy the standard oneÂ¬
dimensional canonical commutation relations. Therefore
X = â€” [X, h] = pi
in â„¢'
(7.8)
Pl4IPl'hl= ,3
y{y+l)Ã±2
 m^X  V^X).
We now introduce canonical coherent states for the ultralocal fields
I \\f > = U[\j/] I 0 >,
(7.9)
where, for each \j/e L , the unitary transformation operator
U[\j/] = expjj" dX d3x [\/(x, X) A+(x, X)  \j/*(x, X)A(x, X)]
(7.10)
It is straightforward to show that
U+[\/] A(x, X) U[\/j = A(x, X) + \jr(x, X),
U+ [\/] A+(x, X) U[f] = A+(x, X) + \/*(x, X);
(7.11)
evidently the same relations hold for B(x, X) and B+(x, X) as well.
77
7.2. Selection of the Coherent States for Ultralocal Fields and the Classical
Limit
Let us employ a Diraclike (first quantized) formulation for functions of
X, and in particular let us set
X) = (X I 1/2 a(x)),
(7.12)
where
( X I K1/2 a(x)) = j^)1/4expj  ^[x  cp(x)]2 + i Xn(x) + i pj (7.13)
a(x) = L [ (p(x) + i 7t(x) ].
Ã2
(7.14)
The expression (7.13) has the form of a conventional canonical coherent state,
i is an arbitrary phase, and I a(x)) = exp[a(x) a+  aâ€™(x) a] I 0 ) = U[a(x)] I 0 ), is
similar to the ordinary coherent state I a)18'19 except that in the present case
a is a function of x. a, a+ are the usual annihilation and creation operators,
which are related to X and p^by the relation
(7.15)
Note well the appearance of h in these various expressions.
In terms of these expressions we have
<\\f I Or(x) I \\f > = <0 I U+[\)/] Or(x) U[\j/] I 0 >
78
â– I
= I dX < O I [B+(x, X) + yâ€˜(x, X)] X [B(x, X) + \/(x, X)] I 0 >
= dX [c(X) + x/(x, X)] X [c(X) + \(t(x, X)]
I
Since c(X) always takes the form c(X) = lexp mX2  yi(X) , it follows that
xT 1 2n 1
Â°i
lim^ _> o I dX c (X) X \j/(x, X) = 0. Consequently
lim^ _> o< VI =lim^_Â»o dX \/*(x, X) X \/(x, X)
j dX \/*(x,
â– 1
= lim;, _>o I dX( K1/2 a(x) I X) X, ( X I K1/2 a(x))
= linv, _>o( 1/2 a(x) IX I K1 /2 a(x))
= (p(x).
(7.16)
Before we calculate , we need to prove several useful
identities. By using
U^/f1/2 a(x)] X U[A*1/2 a(x)] = X + cp(x),
UV1/2 a(x)] pxU[r1/2 a(x)] = p^ + 7i(x),
we can calculate any arbitrary monomial in X's and p^ 's:
79
( h~1/2 oc(x) I ^01 â€¢ â€¢ p0n I K1/2 a(x))
= ( O I ( A, + cp(x) )01. â– â€¢ (pjt+ jc(x) )0n I 0 )
Because of the prefactor fh in the definition of X ( a + a+) ] and p^
[ = a+  a )], all the terms involving X and p^ will go to zero when we
take the limit Ã± â€”> 0. Thus we have
lim/i _> o (tÃ1/2 a(x) I A01 â€¢ â€¢ p0" I fi1/2 a(x)) = cp01(x> â€¢ 7r0n(x). (7.17)
Now with h(â€”, X) = h =  h2^â€” + W{X) , we calculate
dX
2 dX2
A(t) = exp(M: h) ^.exp(  â€”t h)
Ã± Ã±
= x + jt [h, y + iM[h, [h, y 1 +it)3[h, [h, [h, X]]]]
= X + tPi  it2v'(W [v'(X) Pl + PiV'(X)] + â– â– .. (7.18)
After an expectation in the coherent states l/f1/2a(x)) and the limit Ã± Â»0,
we obtain
lim/j 4 o (tÃ1 /2 a(x) I A(t) I K1 /2 a(x))
=
(7.19)
80
where we have used (7.17), and introduced
Vo[cp(x, t)] = lim/j _Â»0V [(p(x, t)]. (7.20)
Notice that Vo(cp) no longer depends on Ã± , but it does contain a vestige of h
in the term 0(p'2(x,t).
We now prove that the result of (7.19) is just the solution
classical canonical equations with the Hamiltonian
d3>
i7T2(x,t) + V0[cp(x, t)] ,
k(x, t) = V0[cp(x, t)].
(7.21)
(7.22)
With (p(x, 0) = (p(x), 7t(x, 0) = k(x), we can use a Taylor series expansion:
cp(x, t) = (p(x, 0) +t cp(x, 0) +i12 (p(x, 0) + 13 ^ + â€¢ â€¢ â–
2 3! at3
=
=
=
In the same way, we can prove that
81
lim/j _> o ( K172 tx(x) I p^(t) I Ti~1/2 a(x)) = 7i(x, t).
Thus
lim^_>0
= lim^ _> o< Â¥ I j dX B+(x, X) X(t) B(x, X) I \\i >
= limÂ¿ _> 0( K1/2 a(x) I X(t) I K1/2 a(x)) = cp(x, t); (7.24)
and evidently
limÂ¿ o< VI ^rCx, t) I y > = k(x, t). (7.25)
According to (7.22), cp(x, t) satisfies the classical equation of motion, namely
(p(x, t) =  Vo[cp(x, t)]. (7.26)
Let us present two examples:
Example 1. Ultralocal PseudoFree Theory
The quantum Hamiltonian of the ultralocal pseudofree field is given
H =  d3xj
dX Bf(x,X)h(â€”,X)B(x,X)
dX
82
where
h(â€”,>.) =  p^2 + + ^2^+ m(y 1/2)h .
M 2 2X2 2
The model function c(X) for the system is determined through (6.7b), and the
result is
C(W = ^eXP!2Vn>4 (727)
Expressing the quantum Hamiltonian in terms of the renormalized
field operators, we have
where we have defined the local operator
nr2 = <3>r+ y(y+l)h2 Or"2+ m(yl)^Or0.
Obviously this definition means that nr neither fits into the canonical
framework nor fulfills the commutation relation [Or(x), nr(y)] = i Â£5(x  y).
From the above analysis, the classical limit of the field operators in the
coherent states denoted by tp(x, t) and 7i(x,t) fits into the classical canonical
equation (7.22), with Vi((p) = 0, and cp(x, t) is the solution of the classical
pseudofree field equation of motion (7.26)20 :
83
cp(x, t) = 0cp'3(x,t)  m2cp(x,t),
where the role of 0cp'3(x,t) is to assure that cp(x, t) > 0 or
that (p(x, t) is not allowed to cross through (p(x, t) = 0, This kind of solution can
be secured if we replace the above equation by the scalecovariant equation of
motion3
cp(x,t) [
For readers interested in the equation of motion of the pseudofree field
operators, Ref. 21 is recommended.
crÂ¿
Example 2. Ultralocal Field with Interaction Potential g(p4 + â€”â€”tp6
2m 2
â– I 'â– I
The quantum Hamiltonian is H = I d3x I dX B+(x, X) h(â€”, X) B(x, X),
dX
and the expressions of h(â€”, X) and c(X) for such a model are
dX
u,d ,, 1 , Y(Y+1 )tÂ¡2 1 â€ž2 .4 g2
Mâ€” = + â€”â€”2 + + 7^
ax 2
2Xâ€˜
2m
* + m (Y 1/2)fi + 8 V/2)^
2 1 m
c(X) = 1 exp ( JmX2 â€”X4
^JY H 2Ã 4mi
(7.28)
The Hamiltonian expressed in terms of the renormalized field operators is
84
H=Ã jtÃ³x) + i [m2 + 2g (Ym3/2)h ]r(x)jd3X ,
J \2 2 m 2 m2 I
T
2*2 2
with nr = d>r + y(Y+l)/i2 r + m(y)/jOr . Since the last two terms in
h(â€”, A,) vanish when we take the classical limit, according to (7.20), the
3A
corresponding classical Hamiltonian when /z â€”> 0 is
Hci = I Jrc2(x) + 0cp'2(x) + im2
J \2 2 2 m2 I
The canonical equations are
7t(x, t) = 0cp'3(x,t)  m2(p(x,t)  4g(p3(x,t) 
and the equation of motion is
cp(x, t) = 0cpâ€˜3(x,t)  m2
according to (7.26).
^Â¿
m2
^Â¿
m2
(7.29)
Again the role of 0 0 or cp(x, t) < 0 ,
namely, that (p(x, t) is not allowed to cross through (p(x, t) = 0, This kind of
solution can be secured if we replace (7.29) by the scalecovariant equation of
motion3
(p(x,t)cp(x, t) =  m2tp2(x,t)  4gcp4(x,t)  â€”2
m2
which is satisfied by the classical limit of the ultralocal field
lim^ _> o< VI ^*r(x, t) I \j/ >, according to Eq. (7.24).
CHAPTER 8
PATHINTEGRAL FORMULATION OF ULTRALOCAL
MODELS
In an earlier chapter, we have pointed out that the pathintegral of the
quartic selfcoupled ultralocal scalar field leads to an trivial (Gaussian) result
when approached by the conventional lattice limit (Chap. 5). However, the
characterization of infinitely divisible distributions allows ultralocal models
alternative operator solutions (Chap. 6) which suggest a new expression of
pathintegral with a nonvanishing, nonclassical potential. In this chapter, we
seek to replace the standard lattice formulation by a nonstandard one which
admits nontrivial results. Specifically, we will use these alternative,
nonperturbative operator solutions to construct nontrivial latticespace path
integrals for nonrenormalizable ultralocal models. As we will see, the
indefinite, nonclassical, singular potential required for the nontriviality in
multicomponent case has different effects on distributions compared to the
singlecomponent case, however the essential property of reweighting the
distribution at the origin is similar. The appearance of additional
nonclasssical, singular potentials suggests that we can not always place the
classical Lagrangian or classical Hamiltonian directly into the pathintegral
formulation, or in other words, a straightforward canonical quantization of
fields with infinite degrees of freedom does not always apply.
86
8.1. Operator Solutions of Ultralocal Models
In this section, we will select certain results, which will be used here,
from Chapter 6 on the operator analysis of ultralocal models15, and put them
into completely proper dimensional forms. Following Chapter 6, the N
component ultralocal field operator can be expressed as
J
(x) = I dA B+(x, A,) A B(x, A)
(8.1)
Where the operators B+(x, A) and B(x, A) are translated Fock operators, defined
through B(x, A) = A(x, A) + c(A), A = Viâ€, while A+(x, A) and A(x, A) denote
conventional irreducible Fock representation operators for which I 0 > is the
unique vacuum, A(x, A) 10 > = 0. for all xeSR""1, Ae91N. The only
nonvanishing commutator is given by
A(x, A), A+(x', A') = 5(xx0 8(AA0.
(8.2)
Obviously, the operators B+(x, A) and B(x, A) follow the same commutation
relation (8.2). For the singlecomponent case, (8.1) becomes
0(x) =
 dA B+(x,
A) A B(x, A).
(8.3)
Renormalized products follow from the operator product expansion:
which suggests the definition of the renormalized square as
sbl
(8.4)
Here we have introduced an auxiliary constant b designed to keep Z
dimensionless. (In the previous chapters, we have generally chosen b=l).
With [â€¢] = dimension (â€¢), we have [b]= [x]1_n. More generally, the
renormalized local powers of the field are given by
= bk lj dX B+(x, X) XÂ¡t â– \ B(x, X) =Zk1011. (8.5)
ii, â€¢ â€¢ â– ,ik = 1,2,3, â€¢ â– â€¢ N and k = 1,2,3, â€¢ â€¢ â–
Occasionally, we need to use the renormalized negative powers of the field
even though they are not local operators. Take the onecomponent case for
example:
dXBf(x,X) (b?ij)kB(x,X) = Mz 01(x)]k,
z
i = 1,2   â€¢ N;
(8.6)
it can formally be extended to k < 0, as long as we define
89
The Hamiltonian of O(N) invariant, Ncomponent ultralocal fields can
be expressed as
dX B+(x, X) h(Vx, X) B(x, X)
dX A+(x, X) h(V\, X) A(x, X).
(8.7)
1 9 2
Where h(V^, X) =  Â¿h V>. + V(X) is a selfadjoint operator in the X variable
alone. The connection between these two relations holds when we insist that
h(Vx, X) c(X) = 0, and in order for 10 > to be the unique ground state of H, it
follows that c(X) g Â£2(9tN). Since [c]2 = [x]1'n[X]â€™N and [X]2= [x]n [h], we have
[c]2 = [x]1"n(1+N/2)[^]â€˜N/2. Therefore, by taking into account of the dimensions,,
the model function may be expressed as
c(X) = ft(2rN)/4baX exp (  y(X, b, ft) j, (8.8)
! r r1 2Ã± I
where a = [ n(lT+N/2)l ] /2(nl). With a proper account of dimensions, the
selfadjoint base Hamiltonian obeys
^ ^ 2
h(Vx, X) =  M2vl+ r(r+2~N^ + m^(rN/2) + bn2bx2+ ^Vi(b?0.
2b
2bX
(8.9)
Obviously, For the singlecomponent case, (8.8) and (8.9) become
Cft) = /Â¡W>/4bIn<3/2tfU/2
W
^mX2  y(X, b, h)
2 n
(8.10)
90
hÂ®/aX,X) = L)Â¡JÃœ + Ã&i^+mÂ«Yl/2) + im2bX2 + lVi(bW . (8.11)
2b SX2 IbX2 2 b
The Hamiltonian may also be expressed in terms of renormalized
fields as
H =j inr2(x) + im2Or2(x) + Vi[Or(x)] Jdx, (8.12)
22 â€” 2 â€” 0
where nr(x) = Or(x) + T(r+2  N)fr2b21 Or(x) I + mh (2T N)b IOr(x) I , and in
terms of bare fields as
H =  jiZn2(x) + lm2Zch2(x) + ^Vi[ZO(x)] jdx (8.13)
^2 2 , , ,  2 02
where ZÃœ (x) = Z0> (x) + r(r+2N)/z2b2Z'310(x) I + mÃ± (2rN)bZ_1 I
For the singlecomponent case, the Hamiltonian becomes
H =  (Â±nr2(x) + lm2chr2(x) + Vi[Or(x)]jdx, (8.14)
=  Â±Zn2(x) + lm2Z02(x) + lVi[ZOr(x)] jdx (8.15)
where n2 = d>2+ yiy+l)h2b2 0>;2 + mÃ±(2y l)b OrÂ° and Zn2 = Z0>2+ Yfy+DfiVo'V3
+ mÃ±(2y l)b oV1 = U2r.
91
The Hamiltonian operator (8.7) readily leads to the Heisenberg field
operator which is given by
â– I
0(x,t) = e*Hâ€˜/Â»
â– I
= dk B+(x, k) k(t) B(x, k)
(8.16)
After this partial review, we turn our attention to the pathintegral
formulation of ultralocal models.
92
8.2 EuclideanSpace PathIntegral Formulation of SingleComponent
Ultralocal Fields
In this section, we will start from the operator solution presented in
Â§8.1 to derive the Euclidean time latticespace formulation. Attention is
focused on the timeordered vacuum to vacuum expectation functional
C[f] = < 0 I Texpj UI dx dt 0(x,t) f(x,t)
I 0>.
(8.17)
Insert (8.3), then we have
C[f] = < 0 I Texd U
pj^j" dx dt j dA, B+(x, X) f(x,t)X(t) B(x, X)
I 0>,
By using the normal ordering technique, C[f] becomes
< 0 IT: exp j dx J dX B+(x, X) { exp [jJ
X) { exp[E dt f(x,t)X(t)] 1} B(x, X)
I 0>.
Notice that only the part inside { } depends on time t . Therefore we can
move the timeordering sign T into the bracket, so we find that
C[f] = < 0 I: exp
j dx j dX B+(x, X) { Texp [j^j
X) { Texpl^J dt f(x,t)X(t)] 1 } B(x, X)
lidxl
= exp  dx  dX c(X) { Texpfh j dt f(x,t)A,(t)] 1} c(X)
lÂ»l
: I 0 >
93
H
de(if(x,t
= exp j dxj dX c(X) { Texp[ I dt (Lf(x,t)X  hQ/c)X, X)) ] 1} c(X)
= lima_Â»o exp Â£ a j dX Cg(X) { Texp [j dt (ifk(x,
t)XhÂ«(a/aX, X))]l}c8(X)
Here in the last step we have employed a latticespace regularization in which
a is the space volume. Let
cs(X) =fcW>/4 ba (X2+ 52)'Y/2exp j  ^m(X2+ 82)  y(X, 5) j,
where 8 is the function of a, a = [n(3/2y)l]/2(nl), and choose 8 so that
a j dX C^fX) = 1. Then we find out that 5 = fh (a b2aF)1/(2yl), F = j dx (x2+l)'7
for y> 1/2; and 5 <*= V7T bn/12(1'n)1 exp[l/(2ab)] for y=l/2. Therefore 8 â€”Â»0, as
aâ€”>0, lima^o c5(X) = c(X), and
C[f] = lima^oll exP
k
if dl (ifk(x,
a dX CÂ§(X) {Texp[ dt (Lfk(X/t)X  hÂ§0/3X, X)) ] 1} Cg(X)
= lima_>0 ]"] a j dX Cg(X) { Texp [J dt ^fk(t)X J
dt hsO/aX, X) ]} Cs(X)
where a^cgfX) represents the normalized ground state of hsO/3X, X), i.e.,
hÂ§0/3X, X) Cg(X) = 0. To the required accuracy in 5, we have
h50/ax, W = +
2b ax2
7(V+1)X 78 h2+ m( 1/2)ft + lm2bx2+ IVj(bX)
2b(X2+ 82)2 2 b
94
and C[f] is reduced to a pathintegral form of single degree quantum
mechanics as
limaron D)i exp f dt {L(kX [Â±bl + 7(Y+1)â€”m(yl/2)Â«
k J J Ã± 2 2b(X2+ 52)2
+ lm2bA.2+ lVi(bX)] } (8.18)
2 b
=lim
aÂ»0
AÂ¿Â¡ (FlDXk)expXj dt{Â± fkXk[Â±bXk+
Y(Y+l^Y82^m(Yl/2)ft
2b(Xk+ 52)2
+^m2bA.k+JVi(b>,k)]}
2 b
Set A,k = aOk, then this expression becomes
C[f] =lima_+0 K  (ÃœDOk) exp^ a j dt {jr^k  [^abOk +
jdt ft
+ m)z(Y1/2)1 + im2abOk+ â€”Vi(abOk)] }
a 2 ab
Y(Y+l)Oka2Y52 n2
2b(Ok+a_252)2 a3
(8.19)
In the formal limit aâ€”>0, we have
C[f] = 9Â¿j DO expj dx dt {lf(x, t)0(x, t)  [IzoV^^Z'V2
+ mfi(r l/2)b oV1 + lm2Z02+â€”Vi(ZO)]}
2 Z
95
dx dt f(x, t)0(x,
, t) j
dtL
(8.20)
Where
L= dx jiZO)2+ y{y+l^1 b Z'V2+ mh(y l/2)b0Â°Z'1+ ^m2Zd>2+ ^Vi(ZO) J,
and notice that we have used the formal factor Z= b/5(0) = lima^o ha.
Obviously, because of the appearance of the additional nonclasssical,
singular potential, the form of L is no longer the classical Lagrangian of the
ultralocal model which reads Lci =j dx ^m2
difference suggests that we can not always place the classical Lagrangian or
classical Hamiltonian directly into the pathintegral formulation, or in other
words, a straightforward canonical quantization of fields with infinitely many
degrees of freedom does not always hold.
96
8.3 Euclidean Space PathIntegral Formulation of MultiComponent
Ultralocal Fields
Following what we did in Â§8.2 and using the results presented in Â§8.1,
we have the timeordered vacuumtovacuum expectation functional
Â¡I
C[f] = < 0 I Texpâ€”I dxdt(x,t)f(x,t)
I 0>.
(8.21)
Substitute (8.1) into the above equation, and it becomes
= < 0 ITexp â€”
j^j dxdt j dA, B+(x,
X) f(x,t)X(t) B(x, X)
I 0>
As we did before, by using the normal ordering technique, we obtain
C[f] = < 0 IT: exp J dx j dX B+(x, X) {exp[J dt i f(x,t)A.(t)] 1 } B(x, A.)
J dx J dX B+(x, A,) { Texp [J dt Uf(x,t)A,(t)]  1 } B(x, A.)
I 0>
= < 0 I: exp
: I 0 >
= exp
= exp
H
M
dX c(X) {Texp[ dt Tf(x,t)X(t)] 1} c(X)
[Ã dtjfix,
[Jdtqlu,
dX c(X) {Texp[ dt (ff(x,t) X  h(Vx, X)) ] 1} c(X)
= lima^o exp
X a j Cg(A.) {Texp [j" dt (jjfk(x,
.t)Xh8(Vx,A,))]l}C8(X)
97
Where in the last step we have employed a latticespace regularization in
which a is the latticecell volume. Let
c5(X) = fi(2rN)/4ba 1 exp ( ^V+ 82)  y(K 5)1,
n2 R2J72 12 n I
(X + 5 )
where a = [ n(lT+N/2)l ] /2(nl), and choose a j dA, CÂ§(X) = 1, then we
have
C[f] = limado]! exP a I dX Cg(X) {Texpl j dt (Ãfk(x,t)X  h5(V^, X)) ] 1} Cg(X)
[Ã dt(iik(x,t
= lima_>o II a j d>. C5O.) {Texp( j dt (  hafV;_, X)) ]) 05ft),
where a1/2cÂ§(A.) denotes the normalized ground state of hsfVx, X), i.e.,
hÂ§(V^, X) cs(X) = 0. Thus, to the required accuracy in 5, we have
h6(Vx, x) = Â±n2vl +
r(r+2N)ft2
2b(X2+52)
rr2)f5 + mA(rN/2) + ^m2bX.2+ ^Vi(bX).
,.2 2.2 2 b
2b(X +5 )
Expressing C[f] in a pathintegral form, we get
C[f] = lima^n ^ j DX exp
jJ dtfk(t) X j
dtLk(X, X)
(8.22)
where
98
^ u2
LX(\, X)=^bX +
rcr+2N)^2
2b(X2+ 62)
nr+2)^252
2 2 2
2b(X + 8 )
m^(r N.) + lm2bx2+ lVi(bX)
2 2 b
It is worth notice that in the cases of vanishing nonclassical, singular
potential
. , T(T+2NW
2b(?t2+ 52)
, another regularized singular potential,
r(T>2)fi252
2 2 2
2b(r+ 52)
> will
take over the reweighting role of the distribution, but only at the origin X, = 0.
y(y+1 )A.2 y82
Unlike the regularized term h2 in (8.18), which is reduced as aÂ»0
2b(X2+ 52)2
y(y+l )fi2
to the positive nonclassical potential â€”â€”â€” when X * 0, the second term in
2bXT
the expression above may be reduced to either a positive, zero or negative
nonclassical potential
r(r+2N)ft2
2bX2
when X * 0 (the third term reduces to zero),
so we can expect that different effects of reweighting the distribution may
happen. But at the point X = 0 the combination of above two terms gives a
regularized negative singular potential  ^(r+2)fi , wblicbl [s similar to of
2b 82 2bS2
N = 1 case. Therefore the reweighting behavior near X = 0 is essentially the
same.
Since the subscript k denotes independent spatial points, we therefore
may write (8.22) as
dt {* fk'^k " Xk) }
n
Set X* = aOk and take the limit, we then obtain
99
dt{j fkOkJUÃaOk, ad>k)}
h a
dt jf(x, t)0(x, t) 
h
l dt L
(4.3)
where we have used the formal factor Z= b/5(0) = lima>o ba, and
L(0, O) = lima_>o \ Lx.(aOk/ aOk)
â– /
u2 * 2 * 0 *2 â€”
dx {1ZO + ^r(r+2N)^2b2Z'31 I + mh(V ^)bZ_110> I + im2ZO + ^Vi(ZO)}
2 2 2 2 2
Once again, the appearance of the additional nonclasssical, singular
potential, has made the form of L no longer the classical Lagrangian of
Ã! 2 21
ultralocal model which reads Lci = I (lo (x) + ^m20 (x) + VilOfx)] jdx. Such a
difference suggests again that we can not always set the classical Lagrangian or
classical Hamiltonian directly in a pathintegral formulation, or in other
words, the canonical quantization for multicomponent fields with infinitely
many degrees of freedom does not always hold.
We are unable to illustrate a path integral construction for N = <*>
directly, although there is always the option to introduce N â€”> Â» outside of
(4.3). On the other hand, the desired generating function for N = can be
formulated in the operator language. In particular, by using the results of the
100
operator solution in Ref. 7 for the infinitecomponent case ( i.e., (3.2)
through (3.7) in Ref. 7 ), we have
4/
C[f] = < 0 iTexpâ€”I dx dt 0(x,t)f(x,t)
0>
= < 0 I Texd Ã
pj^J dxdtj dp(X) B+(x, X) f(x,t) X.(t) B(x, X)
I 0>
= < 0 IT: exp I dx I dp(X) B+(x, X) {exp[ dt â€” f(x,t)X(t)]  1 } B(x, X.)
M
H
= < 0 I: exp I dx I dp(X) B (x, X) {Texp[ I dt â€” f(x,t)X(t)]  1 } B(x, X)
J dt if(x,t
j dt X f(x,t
: I 0 >
: I 0 >
= exp I dxl dp(X) {1Texp[ dt if(x,t)X(t) ] }
jdt F(x'1
= exp
M
dp(X) {1  Texp[
:jdtif(x,t yxj
dt h(V^X)]}
where h(V^, X)l = 0 and dp(X) = g â€”exp  .2y(X, b, /OjdXdQ, 1 < p < 3.
X" 1 n
It would be interesting to try to reformulate this final expression by
means of a path integral, but so far we have not succeeded in doing so.
However, we can still predict that the result is nontrivial, since we have
already obtained the nontrivial characteristic functional of infinite
component fields as the limit of finitecomponent ones, see (6.35) or (6.41).
REFERENCES
1. See, for example, L. I. Schiff, Quantum Mechanics (McGrawHill, New
York, 1968).
2. F. Riesz and B. Nagy, Functional Analysis (Dover, New York, 1990).
3. V. Hutson and J. S. Pym, Applications of Functional Analysis and
Operator Theory (Academic, London, 1980).
4. K. M. Case, Phys. Rev. 80, 797806 (1950).
5. C. Itzykson and J. Zuber, Quantum Field Theory ,(McGrawHill Inc.,
1980);
N. N. Bogoliubov and D. V. Shirkov, Introduction to the Theory of
Quantized Fields , 3rd edition (WileyInterscience, New York, 1979).
6. L. H. Ryder, Quantum Field Theory (Cambridge Univ. Press,
Cambridge, 1985).
7. J. R. Klauder, Acta Phys. AustrÃaca, Suppl. XI, 341 (1973).
8. J. R. Klauder, Phys. Lett. 47B, 523 (1973);
Science 119, 735 (1978).
9. J. R. Klauder, Comm. Math. Phys. 18, 307318 (1970);
Acta Phys. AustrÃaca, Suppl. 8, 227  276 (1971).
10. J. R. Klauder, Lectures in Theoretical Physics, vol. 14B, Ed. by W. E.
Brittin (Colorado Associated Univ. Press, Boulder, Colo., 1973) p. 329.
11. M. Aizenmann, Comm. Math. Phys. 86, 1 (1982);
J. Frohlich, NucÃ. Phys. B 200, 281 (1982);
D. J. E. Callaway, Phys. Rep. 167, 241 (1988).
12. Chengjun Zhu and John R. Klauder, "The Classical Limit of Ultralocal
Scalar Fields" (to appear in J. Math. Phys.)
13. E. LukÃ¡cs, Characteristic Functions (Hafner, New York, 1970)
101
14.
102
J. R. Klauder, "SelfInteracting Scalar Fields and (Non) Triviality" to
be published in the Proceeding of the Workshop on Mathematical
Physics Toward the XXIst Century, Beer Sheva, Israel, March, 1993.
15. Chengjun Zhu and John R. Klauder, "Operator Analysis of
Nonrenormalizable Multicomponent Ultralocal Field Models"
(submitted to Phys. Rev. D.)
16. Chengjun Zhu and John R. Klauder, "Nontrivial Path Integrals for
Nonrenormalizable fields â€”Multicomponent Ultralocal Models",
(submitted to Phys. Rev. D.).
17. O. W. Greenberg, Ann. Phys. 16, 158176 (1961);
A. L. Licht, Ann. Phys. 34, 161186 (1965)
18. K. Hepp, Comm. Math. Phys. 35, 265  277 (1974)
19. J. R. Klauder and B. S. Skagerstam, Coherent States, (World Scientific,
Singapore, 1985 )
20. J. R. Klauder, Phys. Lett. 73B, 152 (1978);
Ann. Phys. 117, 19 (1979)
21. B. S. Kay, J. Phys. A: Math. Gen. 14, 155165 (1981)
22. J. R. Klauder and H. Narnhofer, Phys. Rev. D. 13, 257 (1976)
23. John. R. Klauder, " Covariant Diastrophic Quantum Field Theory ",
Phys. Rev. Lett. 28, 769, (1972)
24. M. Reed, Abstract Nonlinear Wave Equations, Lecture Notes in
Mathematics, 507 (SpringerVerlag, Berlin, 1976)
BIOGRAPHICAL SKETCH
Born in 1963, Chengjun Zhu grew up in the city of Hefei, Anhui
Province, China. She obtained her B. S. and M. S. degrees in physics from
Hefei University of Technology and the University of Science and
Technology of China, respectively. Since September 1988, she has been
working towards her doctoral degree in the Department of Physics, University
of Florida.
103
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a dissertation for the degree of Doctor of Philosophy.
$, [ Ãjl&jvMu.
Joh^R. Klauder, chairman
Professor of Physics
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a dissertation for the degree of Doctor of Philosophy.
J. Robert Buchler
Professor of Physics
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a dissertation for the degree of Doctor of Philosophy.
Pierre Ra
Professo
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in ^cope and
quality, as a dissertation for the degree of Doctor of Philosophy.
Charles F. Hooper
Professor of Physics
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a dissertation for the degree of Doctor of Philosophy.
( 'l/' c
David B. Tanner
Professor of Physics
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a dissertation for the degree
Associate Professor of Mathematics
f Doctor of Philosophy.
z.
Christopher W. Stark
This dissertation was submitted to the Graduate Faculty of the
Department of Physics in the College of Liberal Arts and Sciences and to the
Graduate School and was accepted as partial fulfillment of the requirements for
the degree of Doctor of Philosophy.
April, 1994
Dean, Graduate School
LD
\'\$o
I Â°i ^ 6
. 263
UNIVERSITY OF FLORIDA
3 1262 08554 5555
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