Constraining Axion Inflation with Gravitational Waves across 29 Decades in Frequency.

We demonstrate that gravitational waves generated by efficient gauge preheating after axion inflation generically contribute significantly to the effective number of relativistic degrees of freedom N_{eff}. We show that, with existing Planck limits, gravitational waves from preheating already place the strongest constraints on the inflaton's possible axial coupling to Abelian gauge fields. We demonstrate that gauge preheating can completely reheat the Universe regardless of the inflationary potential. Further, we quantify the variation of the efficiency of gravitational wave production from model to model and show that it is correlated with the tensor-to-scalar ratio. In particular, when combined with constraints on models whose tensor-to-scalar ratios would be detected by next-generation cosmic microwave background experiments, r≳10^{-3}, constraints from N_{eff} will probe or rule out the entire coupling regime for which gauge preheating is efficient.

Leptogenesis from Left-Handed Neutrino Production during Axion Inflation.

We propose that the observed matter-antimatter asymmetry can be naturally produced as a by-product of axion-driven slow-roll inflation by coupling the axion to standard model neutrinos. We assume that grand unified theory scale right-handed neutrinos are responsible for the masses of the standard model neutrinos and that the Higgs field is light during inflation and develops a Hubble-scale root-mean-square value. In this setup, the rolling axion generates a helicity asymmetry in standard model neutrinos. Following inflation, this helicity asymmetry becomes equal to a net lepton number as the Higgs condensate decays and is partially reprocessed by the SU(2)_{L} sphaleron into a net baryon number.

Natural inflation on a steep potential with classical non-Abelian gauge fields.

We propose a model for inflation consisting of an axionic scalar field coupled to a set of three non-Abelian gauge fields. Our model's novel requirement is that the gauge fields begin inflation with a rotationally invariant vacuum expectation value (VEV) that is preserved through identification of SU(2) gauge invariance with rotations in three dimensions. The gauge VEV interacts with the background value of the axion, leading to an attractor solution that exhibits slow roll inflation even when the axion decay constant has a natural value (