Two Puzzles, One Solution: Neutrino Mass and Secluded Dark Matter

TL;DR

This paper proposes a minimal secluded dark matter model linked to neutrino mass generation, where tiny mixing suppresses detection signals, but the model remains consistent with cosmological constraints and explains both neutrino masses and dark matter relic abundance.

Contribution

It introduces a unified framework connecting neutrino masses and secluded dark matter with a suppressed Higgs portal, consistent with current experimental bounds.

Findings

Dark matter relic density is set by p-wave annihilation into dark Higgs particles.

Tiny Higgs mixing angle naturally arises from neutrino mass generation mechanisms.

Model remains consistent with BBN constraints and evades current detection limits.

Abstract

We present a minimal secluded dark-matter (DM) framework based on an extra $U(1)_X$ gauge symmetry. The model contains a Dirac DM particle $\chi$, three heavy neutrinos $N_I$ with masses $M_{N,I}$, and a singlet scalar $R$ that mixes with the Standard Model Higgs doublet $\Phi$ by an angle $\alpha$. A symmetry forbids the $\Phi$-$R$ portal at tree level; the leading portal then arises at one loop from the same Yukawa structures that generate active neutrino masses $m_{\nu,I}$, implying $\tan(2\alpha) \propto \sum_I m_{\nu,I} M^2_{N,I}/(v_h m_H^2)$, where $v_h$ and $m_H$ are the SM Higgs VEV and mass. For heavy-neutrino masses in the multi-TeV range, this yields a naturally tiny mixing, $\tan(2\alpha)\sim 5\times 10^{-11}\left(M_N/10~\mathrm{TeV}\right)^2$, which strongly suppresses DM signals in direct, indirect, and collider searches. For PeV-scale heavy neutrinos the DM-nucleon cross section can instead enter the reach of direct-detection experiments. The visible and dark sectors thermalize at temperatures of order a few times the mass of the lightest heavy neutrino, then subsequently decouple, and typically evolve with a slightly hotter dark bath. In the secluded regime, with $\tan(2\alpha)\ll 1$ and $m_\chi>m_{H_p}$, the relic density is set by $p$-wave annihilation $\chi\bar\chi \to H_p H_p$ (with $H_p$ the Higgs-like particle of the dark sector), and the dark-sector Yukawa couplings required to reproduce the observed abundance are $\sim(0.1\text{-}1)$, as in the standard WIMP case. For heavy-neutrino masses $\gtrsim 10~\mathrm{TeV}$, the mediator decays before nucleosynthesis without spoiling BBN observables, while the tiny portal suppresses present-day signals below current and near-future sensitivities. This links two long-standing puzzles, the absence of DM signals and the smallness of neutrino masses, within a predictive thermal framework.