ALPy Cogenesis

TL;DR

This paper introduces a new leptogenesis mechanism involving heavy right-handed neutrino decay into an axion-like particle and a light fermion, linking neutrino mass generation, dark matter, and baryon asymmetry.

Contribution

It presents a novel cogenesis scenario utilizing two-body decay of heavy RHN with ALP DM, and explores a Dirac fermion variant without lepton number violation.

Findings

Constraints on RHN mass and axion decay constant for successful leptogenesis

Potential observable signatures in CMB, DM searches, and particle physics experiments

Expanded parameter space for ALP and QCD axion DM within experimental reach

Abstract

We propose a novel cogenesis scenario by utilising the two-body decay of heavy right-handed neutrino (RHN) via an effective operator involving an axion-like particle (ALP) dark matter (DM) and a light chiral fermion $\nu_R$. This allows the two-body decay of heavy RHN into $\nu_R$ and ALP thereby generating a lepton asymmetry in $\nu_R$ which later gets transferred to left-handed leptons via sizeable Yukawa coupling with a neutrinophilic Higgs doublet. The asymmetry in left-handed leptons is then converted into baryon asymmetry via electroweak sphalerons. The lepton number violation by heavy RHN also induces a one-loop Majorana mass of $\nu_R$ rendering the light neutrinos to be Majorana fermions. Successful leptogenesis constrain the parameter space in terms of RHN mass and axion decay constant. This has interesting consequences for both ALP and QCD axion DM parameter space within reach of several ongoing and near future experiments. We also propose a Dirac version of this scenario without any total lepton number violation. This leads to a long-lived asymmetric Dirac fermion contributing partially to DM thereby opening up more parameter space for ALP. In addition to axion search experiments, the proposed scenarios can have observable signatures at cosmic microwave background (CMB), DM search as well as terrestrial particle physics experiments.