Singlet-doublet self-interacting dark matter and radiative neutrino mass

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 underabundant SIDM relic due to large annihilation rates into mediator particles, often requiring an extension of the simplest thermal or nonthermal 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 nonthermal 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 Z(2) symmetry can also explain nonzero neutrino mass in scotogenic fashion.

Automated summary

This study explores a scenario of singlet-doublet fermion dark matter, where a light scalar mediator is introduced to explain the velocity-dependent dark matter self-interaction. The doublet fermion provides a nonthermal contribution to the singlet relic, filling the deficit in the thermal relic of singlet SIDM. Additionally, the mixing of the light scalar mediator with the standard model Higgs allows for the detection of such dark matter at terrestrial laboratories.