Transformations of real-time finite-temperature Feynman rules

Abstract

We consider transformations of the 2\ifmmode\times\else\texttimes\fi{}2 propagator matrix in real-time finite-temperature field theory, resulting in transformed n-point functions. As special cases of such a transformation we examine the Keldysh basis, the retarded/advanced RA basis, and a Feynman-like FF\ifmmode\bar\else\textasciimacron\fi{} basis, which differ in this context as to how ``economically'' certain constraints on the original propagator matrix elements are implemented. We also obtain the relation between some of these real-time functions and certain analytic continuations of the imaginary-time functions. Finally, we compare some aspects of these bases which arise in practical calculations.