  We propose a new preheating mechanism through the coupling of the
gravitational field to both the inflaton and matter fields, without direct
inflaton-matter couplings. The inflaton transfers power to the matter fields
through interactions with gravitational waves, which are exponentially enhanced
due to an inflation-graviton coupling. One such coupling is the product of the
inflaton to the Pontryagin density, as in dynamical Chern-Simons gravity. The
energy scales involved are constrained by requiring that preheating happens
fast during matter domination.
