MeV neutrino dark matter: Relic density, lepton flavour violation and electron recoil

TL;DR

This paper explores MeV to GeV right-handed neutrinos as dark matter candidates, analyzing their relic density, neutrino mass generation, and experimental constraints, including lepton flavor violation and direct detection prospects.

Contribution

It provides a comprehensive analysis of right-handed neutrino dark matter parameter space, incorporating relic density, neutrino masses, and experimental bounds, highlighting the impact of lepton flavor violation constraints.

Findings

Dark matter masses are consistent with big-bang nucleosynthesis bounds.

Lepton flavor violation experiments heavily constrain the parameter space.

Electron recoil detection prospects are limited by energy thresholds and mediator mass constraints.

Abstract

Right-handed neutrinos with MeV to GeV mass are very promising candidates for dark matter (DM). Not only can they solve the missing satellite puzzle, the cusp-core problem of inner DM density profiles, and the too-big-to fail problem, {\it i.e.} that the unobserved satellites are too big to not have visible stars, but they can also account for the Standard Model (SM) neutrino masses at one loop. We perform a comprehensive study of the right-handed neutrino parameter space and impose the correct observed relic density and SM neutrino mass differences and mixings. We find that the DM masses are in agreement with bounds from big-bang nucleosynthesis, but that these constraints induce sizeable DM couplings to the charged SM leptons. We then point out that previously overlooked limits from current and future lepton flavour violation experiments such as MEG and SINDRUM heavily constrain the allowed parameter space. Since the DM is leptophilic, we also investigate electron recoil as a possible direct detection signal, in particular in the XENON1T experiment. We find that despite the large coupling and low backgrounds, the energy thresholds are still too high and the predicted cross sections too low due to the heavy charged mediator, whose mass is constrained by LEP limits.