Rescuing Gravitational-Reheating in Chaotic Inflation

We show, within the single-field inflationary paradigm, that a linear non-minimal interaction $\xi\,M_P\,\phi\,R$ between the inflaton field $\phi$ and the Ricci scalar $R$ can result in successful inflation that concludes with an efficient heating of the Universe via perturbative decays of the inflaton, aided entirely by gravity. Considering the inflaton field to oscillate in a quadratic potential, we find that $\mathcal{O}(10^{-1}) \lesssim \xi \lesssim \mathcal{O}(10^2)$ is required to satisfy the observational bounds from Cosmic Microwave Background (CMB) and Big Bang Nucleosynthesis (BBN). Interestingly, the upper bound on the non-minimal coupling guarantees a tensor-to-scalar ratio $r \gtrsim 10^{-4}$, within the range of current and future planned experiments. We also discuss implications of dark matter production, along with the potential generation of the matter-antimatter asymmetry resulting from inflaton decay, through the same gravity portal.