By employing retarded and advanced propagators, Aurenche and Becherrawy
showed how to rewrite the real-time thermal Feynman rules so that the
temperature dependence is removed from the free propagators and transferred to
the vertices. The present paper introduces retarded and advanced field
operators and incorporates all temperature dependence into the interaction term
of the Hamiltonian. Perturbative expansions of the Green functions in the
Hamiltonian formulation give the correct results order by order in perturbation
theory.
The spectrum of the temperature-dependent Hamiltonian contains the thermal
quasiparticles that produce poles in the propagators.Comment: 27 pages, latex, no figure
