Radiative seesaw: Warm dark matter, collider and lepton flavour violating signals

TL;DR

This paper explores a model extending the standard model with right-handed neutrinos and a second Higgs doublet, predicting warm dark matter, lepton flavor violation, and collider signals, with implications for neutrino physics and dark matter composition.

Contribution

It introduces a specific mass spectrum in the radiative seesaw model and analyzes its implications for dark matter, collider phenomenology, and lepton flavor violation.

Findings

The lightest right-handed neutrino acts as warm dark matter, contributing about 10% to the total dark matter density.

Predicted decay branching ratios of charged scalars can be derived from neutrino data.

Large lepton flavor violating signals are expected in muon and tau final states.

Abstract

Extending the standard model with three right-handed neutrinos ($N_k$) and a second Higgs doublet ($\eta$), odd under the discrete parity symmetry $Z_2$, Majorana neutrino masses can be generated at 1-loop order. In the resulting model, the lightest stable particle, either a boson or a fermion, might be a dark matter candidate. Here we assume a specific mass spectrum ($M_1\ll M_2 < M_3 < m_\eta$) and derive its consequences for dark matter and collider phenomenology. We show that (i) the lightest right-handed neutrino is a warm dark matter particle that can give a $\sim$10% contribution to the dark matter density; (ii) several decay branching ratios of the charged scalar can be predicted from measured neutrino data. Especially interesting is that large lepton flavour violating rates in muon and tau final states are expected. Finally, we derive upper bounds on the right-handed neutrino Yukawa couplings from the current experimental limit on $Br(\mu\to e\gamma)$.