  An energetic justification of a thermal component during inflation is given.
The thermal component can act as a heat reservoir which induces thermal
fluctuations on the inflaton field system. We showed previously that such
thermal fluctuations could dominate quantum fluctuations in producing the
initial seeds of density perturbations. A Langevin-like rate equation is
derived from quantum field theory which describes the production of
fluctuations in the inflaton field when acted upon by a simple modeled heat
reservoir. In a certain limit this equation is shown to reduce to the standard
Langevin equation, which we used to construct "Warm Inflation" scenarios in
previous work. A particle physics interpretation of our system-reservoir model
is offered.
