  We show that reheating of the universe occurs spontaneously in a broad class
of inflation models with f(phi)R gravity (phi is inflaton). The model does not
require explicit couplings between phi and bosonic or fermionic matter fields.
The couplings arise spontaneously when phi settles in the vacuum expectation
value (vev) and oscillates, with coupling constants given by derivatives of
f(phi) at the vev and the mass of resulting bosonic or fermionic fields. This
mechanism allows inflaton quanta to decay into any fields which are not
conformally invariant in f(phi)R gravity theories.
