Sterile Neutrino Dark Matter and Low Scale Leptogenesis from a Charged Scalar

TL;DR

This paper introduces a minimal model extending the Standard Model with sterile neutrinos and a charged scalar, providing new mechanisms for dark matter production and baryogenesis that are testable through experiments.

Contribution

It proposes a novel freeze-in production mechanism for sterile neutrino dark matter and demonstrates low-scale leptogenesis via sterile neutrino decays or oscillations.

Findings

Dark matter produced via scalar decays without active-sterile mixing

Leptogenesis achievable near the electroweak scale

Experimental signatures include X-ray lines and scalar production at LHC

Abstract

We show that novel paths to dark matter generation and baryogenesis are open when the Standard Model is extended with three sterile neutrinos $N_i$ and a charged scalar $\delta^+$. Specifically, we propose a new production mechanism for the dark matter particle --a multi-keV sterile neutrino, $N_1$-- that does not depend on the active-sterile mixing angle and does not rely on a large primordial lepton asymmetry. Instead, $N_1$ is produced, via freeze-in, by the decays of $\delta^+$ while it is in equilibrium in the early Universe. In addition, we demonstrate that, thanks to the couplings between the heavier sterile neutrinos $N_{2,3}$ and $\delta^+$, baryogenesis via leptogenesis can be realized close to the electroweak scale. The lepton asymmetry is generated either by $N_{2,3}$-decays for masses $M_{2,3}\gtrsim$ TeV, or by $N_{2,3}$-oscillations for $M_{2,3}\sim$ GeV. Experimental signatures of this scenario include an X-ray line from dark matter decays, and the direct production of $\delta^+$ at the LHC. This model thus describes a minimal, testable scenario for neutrino masses, the baryon asymmetry, and dark matter.