Title An Approach to the Commutation Relations in Quantum Field Theory Author(s) Kakazu, Kiyotaka Citation 琉球大学理工学部紀要. 理学編 = Bulletin of Science & Engineering Division, University of Ryukyus. Mathematics & natural sciences(24): 29-34 Issue Date 1977-09 URL http://hdl.handle.net/20.500.12000/24435 Rights
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An Approach to the Commutation Relations in Quantum Field ... · of the free and interaction Lagrangians, the propagation functions for the asymptotic fields have been determined
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Title An Approach to the Commutation Relations in Quantum FieldTheory
Author(s) Kakazu, Kiyotaka
Citation琉球大学理工学部紀要. 理学編 = Bulletin of Science &Engineering Division, University of Ryukyus. Mathematics &natural sciences(24): 29-34
A general rule for obtaining both the commutator and anticommutator
for any two points in space-time is studied in the case of the absence
of interaction. The anticommutator is determined except for its sign. Examples
of the use of this method are gIven.
29
§ 1. Introduction
As is well known, the commutator for any two points in space-time plays an
important role in quantum field theory. There are several ways of obtaining the
commutator. The usual method is to introduce the canonical conjugates of field
variables and postulate the equal-time commutators between them.
A general rule for obtaning the commutator was first given by Peierls.l)
He treated the commutator as the one being related directly to the Lagrangian of the
system.
The purpose of the present paper is not to obtain any new results, but to
simplify Peierls' method. When the total Lagrangian density of a system consists
of the free and interaction Lagrangians, the propagation functions for the asymptotic
fields have been determined on the basis of the Yang-Feldman formalism. 21··In § 2 and § 3 we present a simple rule for forming the commutation relations,
and the last section ( § 4) is devoted to its application:
§ 2. Commutation relations based on Peierls' method
In this section, we consider general four-dimensional commutation relations
according to Peierls' method.
The free Lagrangian density L of a system is in general given by
where the field operators ,pa are chosen to represent Bose fields, the subscript a
denotes the different types of field as well as the components of each field.
The field equations for .,pa are expressed by2)
•Junier College Div. (Physics), Univ. of the Ryukyus
•• After this work was completed, the author became aware that Nishijima had
already obtained a similar conclusion.:')
30 Kakazu : An Approach to the Commutation Relations in Quantum Field Theory
( 2. 2 )
where a is any differential operator, D(a) a matrix. Let us define the retarded
(JR) and advanced (JA) Green's functions in such a way that
( 2.3 )
A modified Lagrangian L' can be given
( 2.4 )
where L is the Lagrangian of the system, A an infinitesimal parameter, and A any
function of the field operators. For definiteness A=¢t(y) is employed in this section.
Then, the modified Lagrangian density L' becomes
L' (x) = L(x)+ A¢t(y )54 (x -y). ( 2.5 )
Considering the modified field operators ¢~(x) as expansions in powers of A,
we can write them to first order as
( 2.6 )
( 2.7 )
Similarly we can define other modified field operators
( 2.8 )
with
( 2.9 )
According to Peierls, four-dimensional commutation relation between two field