ALP leptogenesis

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.