  Dynamics of the inflaton is studied when it interacts with boson and fermion
fields and in minimal supersymmetric models. This encompasses multifield
inflation models, such as hybrid inflation, and typical reheating models. For
much of the parameter space conducive to inflation, the inflaton is found to
dissipate adequate radiation to have observational effects on density
perturbations and in cases to significantly affect inflaton evolution. Thus,
for many inflation models, believed to yield exclusively isentropic inflation,
the parameter space now divides into regimes of isentropic and nonisentropic
inflation.
