Cosmological Histories in Neutrino Portal Dark Matter

TL;DR

This paper investigates the different cosmological evolution scenarios of a dark sector connected to the Standard Model via a sterile neutrino, analyzing their implications for detection and cosmology.

Contribution

It classifies four distinct cosmological histories of a sterile neutrino portal dark sector and explores their evolution using Boltzmann equations.

Findings

Identified four qualitatively different dark sector histories.

Analyzed the evolution of dark sector temperature and densities.

Discussed experimental and observational probes for these histories.

Abstract

We explore the diverse cosmological histories of a dark sector that is connected to the Standard Model (SM) via a Dirac sterile neutrino. The dark sector consists of a complex scalar and a Dirac fermion dark matter (DM) candidate protected by a global $U(1)$ stabilizing symmetry. Assuming the dark sector has negligible initial abundance and is populated from reactions in the SM thermal plasma during the radiation era, we show that the cosmological histories of the dark sector fall into four qualitatively distinct scenarios, each one characterized by the strengths of the portal couplings involving the sterile neutrino mediator. By solving Boltzmann equations, both semi-analytically and numerically, we explore these thermal histories and transitions between them in detail, including the time evolution of the temperature of the dark sector and the number densities of its ingredients. We also discuss how these various histories may be probed by cosmology, direct detection, indirect detection, collider searches, and electroweak precision tests.