Gravitational Effects on Inflaton Decay
  We point out that the inflaton inevitably couples to all non-conformally
coupled matters gravitationally through an oscillation in the Hubble parameter
or the cosmic scale factor. It leads to particle production during the inflaton
oscillation regime, which is most efficient just after inflation. Moreover, the
analysis is extended to the model with non-minimal inflaton couplings to
gravity, in which the Hubble parameter oscillates more violently. We apply our
results to the graviton production by the inflaton: gravitons are also produced
just after inflation, but the non-minimal coupling does not induce inflaton
decay into the graviton pair.
