Reheating of the universe after inflation withf(ϕ)Rgravity

Abstract

We show that reheating of the universe occurs spontaneously in a broad class of inflation models with $f(\ensuremath{\phi})R$ gravity ($\ensuremath{\phi}$ is the inflaton). The model does not require explicit couplings between $\ensuremath{\phi}$ and bosonic or fermionic matter fields. The couplings arise spontaneously when $\ensuremath{\phi}$ settles in the vacuum expectation value (vev) and oscillates, with coupling constants given by derivatives of $f(\ensuremath{\phi})$ 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 $f(\ensuremath{\phi})R$ gravity theories.