Dissipation coefficients from scalar and fermion quantumfield interactions

Abstract

Dissipation coefficients are calculated in theadiabatic, near thermal equilibrium regime for a large class ofrenormalizable interaction configurations involving a two-stagemechanism, where a background scalar field is coupled to heavyintermediate scalar or fermion fields which in turn are coupled tolight scalar or fermion radiation fields. These interactions are typical of warm inflation microscopic model building.Two perturbative regimes are shown where well defined approximationsfor the spectral functionsapply. One regime is at high temperature, when the masses of both intermediateand radiation fields are less than the temperature scale and where thepoles of the spectral functions dominate. The other regime is at lowtemperature, when the intermediate field masses are much bigger thanthe temperature and where the low energy and low three-momentum regimedominate the spectral functions. The dissipation coefficients in thesetwo regimes are derived. However, due to resummation issues for the high temperature case, only phenomenological approximate estimates are provided for the dissipation in this regime. In the low temperature case, higher loop contributions are suppressedand so no resummation is necessary.In addition toinflationary cosmology, the application of our resultsto cosmological phase transitionsis also discussed.