Gauge Coupling Unification and Non-Equilibrium Thermal Dark Matter

TL;DR

This paper proposes a non-equilibrium dark matter production mechanism involving a massive mediator in models with an extra U(1) gauge symmetry, linking gauge unification with dark matter abundance and reheating temperature.

Contribution

It introduces a novel non-thermal dark matter production scenario connected to gauge unification and predicts specific relations between the mediator scale, reheating temperature, and dark matter abundance.

Findings

Dark matter is produced from the thermal bath after inflation without thermal equilibrium.

The model achieves gauge coupling unification at a high scale, consistent with grand unification.

Reheating temperature can be as high as 10^11 GeV, fixed by the unification scale and mediator properties.

Abstract

We study a new mechanism for the production of dark matter in the universe which does not rely on thermal equilibrium. Dark matter is populated from the thermal bath subsequent to inflationary reheating via a massive mediator whose mass is above the reheating scale, T_R. To this end, we consider models with an extra U(1) gauge symmetry broken at some intermediate scale M, of the order of 10^10 -- 10^12 GeV. We show that not only does the model allow for gauge coupling unification (at a higher scale associated with grand unification) but can naturally provide a dark matter candidate which is a Standard Model singlet but charged under the extra U(1). The intermediate scale gauge boson(s) which are predicted in several E6/SO(10) constructions can be a natural mediator between dark matter and the thermal bath. We show that the dark matter abundance, while never having achieved thermal equilibrium, is fixed shortly after the reheating epoch by the relation T_R^3/M^4. As a consequence, we show that the unification of gauge couplings which determines M also fixes the reheating temperature T_R, which can be as high as 10^11 GeV.