The Plasmon in Hot ${\varphi }^4$ Theory

Abstract

We study the 2-loop resummed propagator in hot $g^2{\varphi }^4$ theory. The propagator has a cut along the whole real axis in the complex energy plane, but for small $g$, the spectral density is sharply peaked around the plasmon. The dispersion relation and the width of the plasmon are calculated at zero {\em and} finite momentum. At large momenta the spectral width vanishes, and the plasmon looses its collectivity and behaves like a non-interacting free particle.

REVTeX, 30 pages, 8 uuencoded ps-figures