Dissipation coefficients from scalar and fermion quantum field
  interactions
  Dissipation coefficients are calculated in the adiabatic, near thermal
equilibrium regime for a large class of renormalizable interaction
configurations involving a two-stage mechanism, where a background scalar field
is coupled to heavy intermediate scalar or fermion fields which in turn are
coupled to light scalar or fermion radiation fields. These interactions are
typical of warm inflation microscopic model building. Two perturbative regimes
are shown where well defined approximations for the spectral functions apply.
One regime is at high temperature, when the masses of both intermediate and
radiation fields are less than the temperature scale and where the poles of the
spectral functions dominate. The other regime is at low temperature, when the
intermediate field masses are much bigger than the temperature and where the
low energy and low three-momentum regime dominate the spectral functions. The
dissipation coefficients in these two 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 suppressed and so no
resummation is necessary. In addition to inflationary cosmology, the
application of our results to cosmological phase transitions is also discussed.
