Electroweak right-handed neutrino portal dark matter

TL;DR

This paper explores a neutrino portal dark matter model involving electroweak scale right-handed neutrinos, analyzing its relic abundance, internal dark sector interactions, and connections to neutrino physics and collider searches.

Contribution

It introduces a comprehensive framework combining neutrino physics with dark matter production, utilizing Particle Swarm Optimization for viable parameter sets and detailed Boltzmann equation solutions.

Findings

Internal dark sector interactions can significantly alter relic density estimates.

Coupled Boltzmann equations are essential for accurate dark matter abundance calculations.

The model provides testable links between neutrino physics, collider searches, and dark matter.

Abstract

We study dark matter coupled to the standard model via electroweak scale right-handed neutrinos in a Type-I seesaw framework. We consider a minimal dark sector containing a fermion $\chi$ and a complex scalar $\phi$ whose only connection to the standard model is through renormalizable Yukawa interactions with right-handed Majorana neutrinos, thus realizing a neutrino portal after seesaw mixing. We discuss three representative realizations of electroweak right-handed neutrinos arising from the Type-I seesaw mechanism, spanning small, large, and ultraweak couplings to the standard model sector, so that the dark particles can either undergo secluded freeze-out or be produced via freeze-in. Instead of merely estimating the order of magnitude of the seesaw couplings, we use the Particle Swarm Optimization algorithm to obtain viable seesaw parameter sets consistent with neutrino data and other constraints, and then compute the coupled evolution of the dark particles and right-handed neutrinos, reproducing the observed dark matter relic abundance in representative benchmark scenarios. For the freeze-in case, we show that internal dark sector interactions can significantly modify the predicted relic density: treating each hidden particle as an independent freeze-in component and simply adding late decays can misestimate the final dark matter abundance by $30\%$, or even $95\%$, depending on the type of internal interactions, compared to a full solution of the coupled Boltzmann equations for all dark species, including the dark sector temperature. Electroweak right-handed neutrino portal dark matter thus provides a robust, testable framework that tightly connects neutrino physics, collider searches for heavy neutral leptons, and the cosmological dark matter relic density, offering a well-motivated benchmark for multi-messenger probes at the high energy frontier.