Pseudo-Dirac Sterile Neutrino Dark Matter

TL;DR

This paper proposes a pseudo-Dirac sterile neutrino dark matter model that avoids X-ray constraints and could help resolve the Hubble tension, with testable predictions for future cosmological measurements.

Contribution

It introduces a new sterile neutrino dark matter model with permutation symmetry, allowing decay channels that evade X-ray constraints and impact cosmological parameters.

Findings

The model avoids X-ray constraints via permutation symmetry.

It predicts an effective number of neutrino species measurable in future experiments.

The model may help alleviate the Hubble tension.

Abstract

Sterile neutrino is a promising dark matter (DM) candidate. However the parameter space of this scenario has almost been ruled out by the X-ray observation results whenever the sterile neutrino is solely produced by the Dodelson-Widrow (DW) mechanism in the early Universe. In this letter we propose an extension to the minimal sterile neutrino DM model by introducing the pseudo-Dirac sterile neutrino, which implies the existence of two nearly degenerate Majorana states $\hat N_{1,2}^{}$, and a permutation symmetry. The heavy state $\hat N_1$ is produced via the DW mechanism, and the light state $\hat N_2$, which serves as the DM, is produced from the decay of $\hat N_1$ in the early Universe. The X-ray constraint is avoided by the permutation symmetry, which forbidden the two-body decay of the DM into active neutrinos and photon. A promising signal of this scenario is the effective number of neutrino species, which will be precisely measured in future experiments, such as CMB stage IV. We further study the impact of this model on the cosmological parameters. The Markov Chain Monte Carlo analysis for the Planck + BAO+R19 data gives $H_0=69.2_{-0.59}^{+0.58}$, which may relieve the Hubble tension.