Warm Dark Matter in Two Higgs Doublet Models

TL;DR

This paper proposes a two Higgs doublet model where a neutral scalar acts as warm dark matter, explaining relic density, the 3.5 keV X-ray line, and making testable predictions for future experiments.

Contribution

It introduces a novel warm dark matter candidate within two Higgs doublet models with seesaw neutrino masses, linking cosmological and astrophysical observations.

Findings

The scalar an account for the relic density of dark matter.

The model explains the 3.5 keV X-ray anomaly via scalar decay.

Constraints on right-handed neutrino mass and lifetime are established.

Abstract

We show that a neutral scalar field, \sigma, of two Higgs doublet extensions of the Standard Model incorporating the seesaw mechanism for neutrino masses can be identified as a consistent {\it warm} dark matter candidate with a mass of order keV. The relic density of $\sigma$ is correctly reproduced by virtue of the late decay of a right-handed neutrino N participating in the seesaw mechanism. Constraints from cosmology determine the mass and lifetime of N to be M_N = 25 GeV - 20 TeV and \tau_N = (10^{-4} - 1) sec. These models can also explain the 3.5 keV X-ray anomaly in the extra-galactic spectrum that has been recently reported in terms of the decay \sigma \to \gamma \gamma. Future tests of these models at colliders and in astrophysical settings are outlined.