Stochastic Gravitational Waves from Inflaton Decays
  Due to the universality of gravitational interactions, it is generally
expected that a stochastic gravitational wave (GW) background could form during
the reheating period when the inflaton perturbatively decays with the emission
of gravitons. Previously, only models in which the inflaton dominantly decays
into a pair of light scalar and/or fermion particles were considered in the
literature. In the present paper, we focus on the cases with a vector particle
pair in the final decay product. The differential decay rates for the
three-body gravitational inflaton decays are presented for two typical
couplings between the inflaton and vector fields, from which we predict their
respective GW frequency spectra. It turns out that, similar to the scalar and
fermion cases, the obtained GW spectra is too high in frequency to be observed
by the current and near-future GW detection experiments and calls for a new
design of high-frequency GW detectors.
