Cogenesis of visible and dark matter in a scotogenic model

TL;DR

The paper addresses the challenge of jointly explaining the baryon asymmetry and dark matter within a single, minimal framework. It introduces a cogenesis mechanism in the scotogenic model, where the CP-violating decay of a heavy $N_2$ seeds both the visible BAU and a multipartite dark sector, and a sub-GeV dark matter candidate $N_1$ is produced by the late decay of the inert doublet $\eta$ in a freeze-in regime. The authors derive the CP asymmetry, solve coupled Boltzmann equations governing the two-sector evolution, and perform a comprehensive parameter scan to identify regions that satisfy neutrino oscillation data, LFV bounds, BAU, and the observed DM relic density ($\Omega_{ ext{DM}} h^2 = 0.12$). They find that a viable region exists with $M_{N_1} \approx 9.6\ \mathrm{MeV}$ and a characteristic hierarchy $M_{N_3} > M_{N_2} \gg M_{N_1}$, where late-time NLSP decay and scattering dynamics regulate the DM abundance while remaining compatible with structure-formation bounds. The work provides a minimal, testable unification of neutrino masses, leptogenesis, and sub-GeV dark matter with distinct late-time dynamics and structure-formation-consistent predictions.

Abstract

Within a scotogenic neutrino mass model we explore the cogenesis of matter from the CP violating decay of a heavy $\mathbb{Z}_2$-odd right handed neutrino that simultaneously populates the visible and a multipartite dark sector. The relic density of a sub-GeV scale freeze-in dark matter is generated by the late time decay of the next-to-lightest dark particle dynamically regulated by an interplay with the thermal scattering processes. We show that this model can simultaneously explain visible matter asymmetry and provide a cosmologically viable sub-GeV dark matter while remaining in consonance with the neutrino parameters and flavour observables.

Figures (8)

• Figure 1: Cogenesis of matter within the minimal scotogenic model
• Figure 2: Neutrino mass generation in the Scotogenic model
• Figure 3: Tree level (\ref{['fig:N2_decay_tree']}) and $N_3$ the leading one loop (\ref{['fig:N2_decay_loop_self']} and \ref{['fig:N2_decay_loop_vertex']}) decay of $N_2$.
• Figure 4: Left panel \ref{['fig:reac_den']} shows the decay and scattering reaction densities of the inert scalar doublet with respect to $z$. The vertical dashed line represents the equality of both these reaction densities. All other reaction densities utilized in Eq. \ref{['eq:boltz_full']} are shown in the right panel \ref{['fig:reac_den_all']} for the benchmark point given in Table \ref{['tab:bp_details']}.
• Figure 5: Evolution of abundances for various species involved in cogenesis for the benchmark point in Table \ref{['tab:bp_details']}.