Ricci Reheating
  We present a model for viable gravitational reheating involving a scalar
field directly coupled to the Ricci curvature scalar. Crucial to the model is a
period of kination after inflation, which causes the Ricci scalar to change
sign thus inducing a tachyonic effective mass $m^{2} \propto -H^2$ for the
scalar field. The resulting tachyonic growth of the scalar field provides the
energy for reheating, allowing for temperatures high enough for thermal
leptogenesis. Additionally, the required period of kination necessarily leads
to a blue-tilted primordial gravitational wave spectrum with the potential to
be detected by future experiments. We find that for reheating temperatures
$T_{\rm RH} \lesssim 1$ GeV, the possibility exists for the Higgs field to play
the role of the scalar field.
