Singlet-Doublet Self-interacting Dark Matter and Radiative Neutrino Mass

TL;DR

This paper proposes a singlet-doublet fermion dark matter model with a light scalar mediator that explains small-scale structure issues, provides a non-thermal relic component, and connects to neutrino mass generation, with experimental constraints from direct detection.

Contribution

It introduces a novel singlet-doublet fermion dark matter scenario with a light mediator and a mechanism for non-thermal relic enhancement, also linking to neutrino mass via a scotogenic model.

Findings

The model achieves velocity-dependent self-interactions compatible with astrophysical observations.

It predicts detectable signals at terrestrial laboratories like XENON1T and CRESST-III.

The extended sector can generate neutrino masses consistent with observations.

Abstract

Self-interacting dark matter (SIDM) with a light mediator is a promising scenario to alleviate the small-scale problems of the cold dark matter paradigm while being consistent with the latter at large scales, as suggested by astrophysical observations. This, however, leads to an under-abundant SIDM relic due to large annihilation rates into mediator particles, often requiring an extension of the simplest thermal or non-thermal relic generation mechanism. In this work, we consider a singlet-doublet fermion dark matter scenario where the singlet fermion with a light scalar mediator gives rise to the velocity-dependent dark matter self-interaction through a Yukawa type attractive potential. The doublet fermion, by virtue of its tiny mixing with the singlet, can be long-lived and can provide a non-thermal contribution to the singlet relic at late epochs, filling the deficit in the thermal relic of singlet SIDM. The light scalar mediator, due to its mixing with the standard model Higgs, paves the path for detecting such SIDM at terrestrial laboratories leading to constraints on model parameters from CRESST-III and XENON1T experiments. Enlarging the dark sector particles by two more singlet fermions and one scalar doublet, all odd under an unbroken $\mathcal{Z}_2$ symmetry can also explain non-zero neutrino mass in scotogenic fashion.