Constraining Inflation With Gravitational Waves From Preheating

We study gravitational wave production during Abelian gauge-field preheating following axion inflation. Prior work showed that, in regimes in which preheating transitions the Universe to a completely radiation-dominated state, a near-detectable level of gravitational waves is produced. These gravitational waves can contribute to the radiation energy budget of the Universe at a level which will be probed by upcoming cosmic microwave background experiments through the effective number of neutrino species. In this work we explore the relationship between the specific model of inflation and the dynamics of gauge-preheating with the resulting gravitational wave production, finding that the relationship between the two is qualitatively generic. As a result, gravitational waves from preheating could provide the strongest constraints on inflation couplings to gauge-fields.