Fourth generation Majorana neutrino, dark matter and Higgs physics

TL;DR

This paper explores a fourth-generation neutrino as a dark matter candidate and its implications for Higgs physics, analyzing current collider data and dark matter detection prospects.

Contribution

It introduces a model with a stable fourth Majorana neutrino that affects Higgs decay and dark matter detection, constrained by LHC data.

Findings

Lightest fourth Majorana neutrino mass range: 41-59 GeV

Predicted spin-independent DM-nucleus cross-section near Xenon100 limits

Potential detectability of the neutrino in upcoming Xenon1T experiments

Abstract

We consider extensions of the standard model with fourth generation fermions (SM4) in which extra symmetries are introduced such that the transitions between the fourth generation fermions and the ones in the first three generations are forbidden. In these models, the stringent lower bounds on the masses of fourth generation quarks from direct searches are relaxed, and the lightest fourth neutrino is allowed to be stable and light enough to trigger the Higgs boson invisible decay. In addition, the fourth Majorana neutrino can be a subdominant but highly detectable dark matter component. We perform a global analysis of the current LHC data on the Higgs production and decay in this type of SM4. The results show that the mass of the lightest fourth Majorana neutrino is confined in the range $\sim 41-59$ GeV. Within the allowed parameter space, the predicted effective cross-section for spin-independent DM-nucleus scattering is $\sim 3\times 10^{-48}-6\times 10^{-46} \text{cm}^{2}$, which is close to the current Xenon100 upper limit and is within the reach of the Xenon1T experiment in the near future. The predicted spin-dependent cross sections can also reach $\sim 8\times 10^{-40}\text{cm}^{2}$.