Heisenberg and interaction representations in thermo field dynamics

T. S. Evans*, I. Hardman, H. Umezawa, Y. Yamanaka

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)


In this paper the so-called α degree of freedom appearing in thermal quantum field theory is discussed, using thermo field dynamics (TFD). This paper is confined to stationary thermal situations, both nonequilibrium and equilibrium. The main result is that when the stationary number distribution differs from the equilibrium one the use of time ordered and antitime ordered formalisms picks up α = 1 and α = 0, in contrast to the general belief that the Feynman diagram method is usable for any other a as well. This situation in TFD will be compared with the other approaches. The reason why the Feynman diagram method becomes available for any a in the case of the equilibrium distributions is also studied.

Original languageEnglish
Pages (from-to)370-378
Number of pages9
JournalJournal of Mathematical Physics
Issue number1
Publication statusPublished - 1992
Externally publishedYes

ASJC Scopus subject areas

  • Statistical and Nonlinear Physics
  • Mathematical Physics


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