Gravitational waves from gauge preheating

Abstract

We study gravitational wave production during Abelian gauge-field preheating following inflation. We consider both scalar and pseudoscalar inflaton models coupled directly to Abelian 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. These gravitational waves can contribute to the radiation energy budget of Universe at a level which will be probed by upcoming cosmic microwave background experiments through N eff . 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. We compute the gravitational topological charge and demonstrate that gauge preheating following axion inflation may be responsible for the matter-antimatter asymmetry of the Universe via gravitational leptogenesis.

Constraining axion inflation with gravitational waves from preheating

“…Our numerical approach is very similar to that employed in Ref. [46]. We numerically integrate the classical equations of motion of the inflaton, Eq.…”

“…There are two differences in our numerical implementation relative to that in Ref. [46]. First, we have improved our procedure for obtaining the power spectra of the gauge fields at the end of inflation.…”

“…In contrast to Refs. [40,46], here we more carefully account for the backreaction of the gauge fields onto the background quantities. At the range of couplings we explore, the approximations used to derive the analytic results Eqs.…”

“…During preheating, significant energy density can be deposited into subhorizon gravitational waves which, as in Ref. [46], may be constrained by CMB and BBN measurements of the total radiation density in species beyond the standard model,…”

“…Subsequently, we extended this work in Ref. [46] to compute the gravitational wave spectrum produced by the dynamics of gauge preheating. The surprising result was that the (over-) production of gravitational radiation provides the strongest probe of (or constraints on) the coupling scale between the axion and gauge fields.…”