Gravitational Waves from Gauge Preheating

We study gravitational wave production during Abelian gauge-field preheating following inflation. We consider both scalar and pseudoscalar inflaton models coupled directly to Abelian U(1) gauge fields via either a dilatonic coupling to the gauge-field kinetic term or an axial coupling to a Chern-Simons term. In both cases gravitational waves are produced efficiently during the preheating phase, with a signature louder than most cosmological signals. For axially coupled fields the resulting gravitational wave spectrum is helically polarized - a unique feature that can be used to differentiate it from other stochastic gravitational wave backgrounds.