Wash-in leptogenesis after axion inflation

TL;DR

This paper introduces a novel leptogenesis mechanism called wash-in leptogenesis, driven by axion inflation, which generates baryon asymmetry through primordial charge asymmetries reprocessed by right-handed neutrinos, with implications for cosmological observations.

Contribution

It proposes a new leptogenesis scenario utilizing axion inflation coupled to hypercharge, accounting for flavor effects and providing bounds on right-handed neutrino masses.

Findings

Viable scenarios for wash-in leptogenesis identified.

Lower bound of 10^5 to 10^9 GeV on RHN mass established.

Potential observational signatures in magnetic fields and gravitational waves.

Abstract

CP violation and the violation of baryon-minus-lepton number B-L do not necessarily have to occur simultaneously in order to accomplish successful leptogenesis. Instead, it suffices if new CP-violating interactions at high energies result in primordial charge asymmetries, which are then reprocessed into a nonvanishing B-L asymmetry by right-handed neutrinos (RHNs) at lower energies. In this paper, we study this novel mechanism known as "wash-in leptogenesis", utilizing axion inflation as the source of high-scale CP violation. We specifically consider axion inflation coupled to the Standard Model hypercharge sector, which results in the dual production of hypermagnetic helicity and fermionic charge asymmetries. Although the survival of these charges is endangered by sphaleron processes, magnetic diffusion, and the chiral plasma instability, we find a large range of viable scenarios. We consistently account for RHN flavor effects and coherence among the Standard Model lepton flavors across a wide range of RHN masses. We find a lower bound of 10^(5...9) GeV on the mass of the lightest RHN involved in wash-in leptogenesis, depending on the onset of turbulence in the chiral plasma and the Hubble scale of inflation. Our model is representative of a broader class of new leptogenesis scenarios and suggests interesting observational signatures with regard to intergalactic magnetic fields, primordial black holes, and gravitational waves.