Probing the fourth generation Majorana neutrino dark matter

TL;DR

This paper investigates the detectability of a stable fourth-generation Majorana neutrino as a dark matter candidate, showing current experiments can constrain its mass and predict measurable scattering cross sections.

Contribution

It introduces a model where the fourth-generation Majorana neutrino's stability is protected by a U(1) gauge symmetry and analyzes its detection prospects in current experiments.

Findings

Neutrino mass constrained to be above top quark mass by Xenon100 data.

Predicted spin-independent cross section around 1.5×10⁻⁴⁴ cm², within reach of future experiments.

Spin-dependent cross section in the range detectable by IceCube.

Abstract

Heavy fourth generation Majorana neutrino can be stable and contribute to a small fraction of the relic density of dark matter (DM) in the Universe. Due to its strong coupling to the standard model particles, it can be probed by the current direct detection experiments even it is a subdominant component of the whole halo DM. Assuming that it contributes to the same fraction of the local halo DM density as that of the DM relic density, we show that the current Xenon100 data constrain the mass of the stable Majorana neutrino to be greater than the mass of the top quark. In the mass range between 200 GeV and a few hundred GeV, the effective spin-independent cross section for the neutrino elastic scattering off nucleon is insensitive to the neutrino mass and is predicted to be $\sim 1.5\times 10^{-44} cm^2$, which can be reached by the direct DM search experiments soon. In the same mass region the predicted effective spin-dependent cross section for the heavy neutrino scattering off proton is in the range $2\times 10^{-40} cm^2\sim 2\times 10^{-39} cm^2$, which is within the reach of the ongoing IceCube experiment. We demonstrate such properties in a fourth generation model with the stability of the fourth Majorana neutrino protected by an additional generation-dependent U(1) gauge symmetry.