Sterile neutrino dark matter in warped extra dimensions

TL;DR

This work analyzes sterile neutrino dark matter within a five-dimensional warped Randall-Sundrum framework with bulk fields, proposing radion decays as the primary production mechanism around the electroweak scale. Warp-factor suppressions naturally yield tiny effective 4D parameters and small wavefunction overlaps, enabling keV to MeV scale sterile masses without fine-tuning. A Boltzmann-equation treatment of radion-mediated production yields relic densities that can match observations, with concrete Planck- and TeV-brane Majorana-mass setups that satisfy Lyman-α and X-ray constraints. The results demonstrate that warped extra dimensions can host warm or cold sterile DM without relying on large active-sterile mixing, highlighting distinctive radion- and bulk-neutrino phenomenology for future exploration.

Abstract

We consider a (long-lived) sterile neutrino dark matter scenario in a five dimensional (5D) warped extra dimension model where the fields can live in the bulk, which is partly motivated from the absence of the absolutely stable particles in a simple Randall-Sundrum model. The dominant production of the sterile neutrino can come from the decay of the radion (the scalar field representing the brane separation) around the electroweak scale. The suppressions of the 4D parameters due to the warp factor and the small wave function overlaps in the extra dimension help alleviate the exceeding fine-tunings typical for a sterile neutrino dark matter scenario in a 4D setup.