  Our present understanding of the reheating phase is incomplete due to a lack
of observations. Apart from its cosmological implications, the reheating should
play a vital role in particle physics and inflation model building.
Conventionally reheating dynamics are modeled by invoking arbitrary coupling
among the inflaton and daughter fields. Such an approach lacks robust
cosmological predictions due to its arbitrary couplings and is difficult to
verify through observation. In this paper, we propose a minimal reheating
scenario where the inflaton is coupled with all the daughter fields only
gravitationally. Besides being successful in reheating the Universe, the
scenario offers a strong cosmological prediction of the primordial
gravitational wave spectrum and discards a large number of possible models of
dark matter and inflation that are otherwise consistent with Planck.
