Singlet-Doublet Majorana Dark Matter and Neutrino Mass in a minimal Type-I Seesaw Scenario

TL;DR

This paper presents a minimal extension of the Standard Model that explains dark matter as a Majorana particle and accounts for neutrino masses via a Type-I Seesaw, with implications for direct detection and collider searches.

Contribution

It introduces a novel model combining singlet-doublet Majorana dark matter with a Type-I Seesaw mechanism in a minimal setup, including a gauged $U(1)_{B-L}$ symmetry.

Findings

Dark matter is a Majorana particle avoiding $Z$-mediated constraints.

Parameter space consistent with relic density and direct detection limits identified.

Collider search strategies are proposed for the model.

Abstract

In a bid to simultaneous explanation of dark matter (DM) and tiny but non-zero masses of left-handed neutrinos, we propose a minimal extension of the Standard Model (SM) by a vector-like fermion doublet and three right handed (RH) singlet neutrinos. The DM arises as a mixture of the neutral component of the fermion doublet and one of the RH neutrinos, both assumed to be odd under an additional $\mathcal{Z}_2$ symmetry. As a result, the DM emerges to be a dominantly Majorana particle and escapes from $Z$-mediated direct search constraints to mark a significant difference from singlet-doublet Dirac DM. The other two $\mathcal{Z}_2$ even heavy RH neutrinos give rise masses and mixing of light neutrinos via Type-I Seesaw mechanism. The particle content automatically allows us to extend the model by a gauged $U(1)_{B-L}$ symmetry, which is anomaly free and brings an additional portal between DM and SM particles. Relic density and direct search allowed parameter space for both the cases are investigated through detailed numerical scan, while collider search strategies are also indicated.