ALPy Cogenesis

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 $ν_R$. This allows the two-body decay of heavy RHN into $ν_R$ and ALP thereby generating a lepton asymmetry in $ν_R$ 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 $ν_R$ 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.

Figures (8)

• Figure 1: Processes responsible for creating asymmetry in $\nu_R$.
• Figure 2: One-loop contribution to Majorana mass of $\nu_R$.
• Figure 3: Evolution of comoving number densities in minimal ALPy cogenesis.
• Figure 4: Allowed parameter space of minimal ALPy cogenesis scenario in $f-M_1$ plane considering dimensionless couplings $\tilde{\lambda}_{i\alpha}, y_{\alpha \beta}\sim 10^{-2}$. The shaded regions are disfavored leaving only the white region allowed for minimal ALPy cogenesis.
• Figure 5: Processes responsible for creating asymmetry in $\nu_R$ in Dirac ALPy cogenesis.