Right-handed Neutrino Dark Matter in a U(1) Extension of the Standard Model

TL;DR

This paper explores a minimal $U(1)$ extension of the Standard Model where a right-handed neutrino acts as dark matter, analyzing phenomenological constraints and viable parameter space, especially for a $U(1)_{(B-L)_3}$ symmetry.

Contribution

It provides a detailed phenomenological analysis of right-handed neutrino dark matter in a specific $U(1)$ extension, including bounds and detection prospects, which was not previously detailed.

Findings

Dark matter mass bound of $\lesssim 2$ TeV under high-scale perturbativity.

Strong direct detection constraints if the scalar mixes significantly with the Higgs.

Viable parameter space remains for small mixing, accessible via future collider and indirect detection.

Abstract

We consider minimal $U(1)$ extensions of the Standard Model in which one of the right-handed neutrinos is charged under the new gauge symmetry and plays the role of dark matter. In particular, we perform a detailed phenomenological study for the case of a $U(1)_{(B-L)_3}$ flavoured $B-L$ symmetry. If perturbativity is required up to high-scales, we find an upper bound on the dark matter mass of $m_\chi\lesssim2$ TeV, significantly stronger than that obtained in simplified models. Furthermore, if the $U(1)_{(B-L)_3}$ breaking scalar has significant mixing with the SM Higgs, there are already strong constraints from direct detection. On the other hand, there remains significant viable parameter space in the case of small mixing, which may be probed in the future via LHC $Z^\prime$ searches and indirect detection. We also comment on more general anomaly-free symmetries consistent with a TeV-scale RH neutrino dark matter candidate, and show that if two heavy RH neutrinos for leptogenesis are also required, one is naturally led to a single-parameter class of $U(1)$ symmetries.