Enabling Thermal Dark Matter within the Vanilla $L_\mu$-$L_\tau$ Model

TL;DR

This paper explores how the $L__$-$L__$ model can accommodate thermal dark matter in the sub-GeV range, emphasizing the impact of early-universe matter domination and the potential of upcoming experiments to probe this parameter space.

Contribution

It introduces a detailed analysis of thermal dark matter within the $L__$-$L__$ model, considering early-universe effects and experimental prospects, which is a novel approach in this context.

Findings

Next-generation experiments will probe large regions of the viable parameter space.

Matter-dominated era affects the relic density calculations.

Sub-GeV thermal dark matter remains testable with upcoming accelerators.

Abstract

Thermal dark matter is a compelling setup that has been probed by a multitude of experiments, mostly in the GeV-TeV mass range. The thermal paradigm in the sub-GeV range is about to experience the same experimental test with the next generation of low-energy accelerators and light dark matter detectors. Motivated by this, we investigate thermal dark matter in the $L_\mu-L_\tau$ and assess how the introduction of a matter-dominated era impacts the parameter that yields the correct relic density. Interestingly, we show that the projected experiments, such as MuSIC, FCC-ee, and LDMX, will probe a large region of the viable parameter space that yields the correct relic density. In the GeV-TeV mass regime, the usual large-scale detectors push the sensitivity. Our work highlights the rich interplay between early-universe dynamics, dark matter phenomenology, and the discovery potential of next-generation experiments.