Thermal and non-thermal production of dark matter via Z'-portal(s)

TL;DR

This paper investigates how Z'-portal models can produce the correct dark matter abundance in the early universe, analyzing weak-scale and very massive mediators, and exploring thermalisation effects on relic density.

Contribution

It provides a detailed analysis of dark matter production via Z'-portals, including kinetic mixing constraints, relic abundance calculations, and the impact of thermalisation processes.

Findings

Small kinetic mixing values can produce the observed dark matter density.

Relic abundance constrains the relationship between reheating temperature and interaction scale.

Thermalisation significantly affects relic abundance calculations.

Abstract

We study the genesis of dark matter in the primordial Universe for representative classes of Z'-portals models. For weak-scale Z' mediators we compute the range of values of the kinetic mixing allowed by WMAP/PLANCK experiments corresponding to a FIMP regime. We show that very small values of the kinetic coupling (1.e-12 < delta < 1.e-11) are sufficient to produce the right amount of dark matter. We also analyse the case of very massive gauge mediators, whose mass is larger than the reheating temperature, "T_RH", with a weak-scale coupling to ordinary matter. Relic abundance constraints then impose a direct correlation between T_RH and the effective scale "Lambda" of the interactions: Lambda ~ 1.e3--1.e5 * T_RH. Finally we describe in some detail the process of dark thermalisation and study its consequences on the computation of the relic abundance.