ALP leptogenesis

TL;DR

This paper introduces a new leptogenesis mechanism involving axion-like particles decaying into right-handed neutrinos, which reduces the required neutrino mass scale and predicts an early matter-dominated era in the universe.

Contribution

It presents a novel leptogenesis model using ALP decay into RHNs, lowering the mass scale needed and linking to supersymmetric scenarios with dark matter implications.

Findings

ALP leptogenesis requires ALP mass > 10^4 GeV and decay constant > 10^11 GeV.

The mechanism reduces the RHN mass or tuning needed by two orders of magnitude.

It predicts an early matter domination period induced by the ALP.

Abstract

We propose a novel realisation of leptogenesis that relies on the out-of-equilibrium decay of an axion-like particle (ALP) into right-handed Majorana neutrinos (RHNs) in the early Universe. With respect to standard thermal leptogenesis, our mechanism lowers by two orders of magnitude the RHN mass, or the tuning in the RHN mass splittings, needed to reproduce the baryon asymmetry of the Universe and neutrino masses. We find that ALP leptogenesis requires $m_a > 10^{4}$ GeV and $f_a > 10^{11}$ GeV for the ALP mass and decay constant, and predicts an early period of matter domination induced by the ALP in parts of its parameter space. We finally provide a viable supersymmetric realisation of ALP leptogenesis where the ALP is the $R$-axion, which accommodates GeV gravitino dark matter and predicts RHN below 10 TeV.