Gravitational Portals with Non-Minimal Couplings
  We consider the effects of non-minimal couplings to curvature of the form
$\xi_S S^2 R$, for three types of scalars: the Higgs boson, the inflaton, and a
scalar dark matter candidate. We compute the abundance of dark matter produced
by these non-minimal couplings to gravity and compare to similar results with
minimal couplings. We also compute the contribution to the radiation bath
during reheating. The main effect is a potential augmentation of the maximum
temperature during reheating. A model independent limit of
$\mathcal{O}(10^{12})$ GeV is obtained. For couplings $\xi_S \gtrsim
\mathcal{O}(1)$, these dominate over minimal gravitational interactions.
