Feynman’s Perturbative Theory of the Thermal Green’s Function

Carlo Jacoboni

Giampaolo Co’

To date, we have primarily employed the Green function technique to study transport phenomena. As we have seen, the method is very powerful and can be used in several problems. However, perturbation theory, in terms of Feynman diagrams, can only be applied when the concept of quasiparticles is applicable. The simplest way to describe transport without reference to quasiparticles is through hydrodynamics, which explains the long-wavelength, long-time dynamics of a system close to thermal equilibrium. It is a powerful non-perturbative technique for describing transport in materials.

Eleftherios N. Economou

Girish S. Setlur

In this short write-up we argue that self-consistent diagrammatic perturbation theory(i.e. Feynman diagrams) for the one-particle Green function is unable to capture some important qualitative features no matter how self-consistently the Green functions are obtained. This write-up is intended to highlight the short-comings of perturbation theory and also tout the advantages of the sea-boson technique(hep-th/9706006).

Eleftherios N. Economou