# Improved bounds on $\mathbb{Z}_{3}$ singlet dark matter

## TL;DR

This paper refines theoretical bounds and improves the treatment of thermal freeze-out for $ ext{Z}_3$ scalar singlet dark matter, providing updated constraints and predictions for detection experiments.

## Contribution

It introduces stronger stability bounds, incorporates dark matter temperature evolution in relic calculations, and refines detection signal predictions for $ ext{Z}_3$ singlet dark matter.

## Key findings

- Stronger lower limits on direct detection cross section.
- Modified relic abundance calculations including dark matter temperature evolution.
- Large semi-annihilation region will be tested by XENONnT.

## Abstract

We reconsider complex scalar singlet dark matter stabilised by a $\mathbb{Z}_{3}$ symmetry. We refine the stability bounds on the potential and use constraints from unitarity on scattering at finite energy to place a stronger lower limit on the direct detection cross section. In addition, we improve the treatment of the thermal freeze-out by including the evolution of the dark matter temperature and its feedback onto relic abundance. In the regions where the freeze-out is dominated by resonant or semi-annihilation, the dark matter decouples kinetically from the plasma very early, around the onset of the chemical decoupling. This results in a modification of the required coupling to the Higgs, which turns out to be at most few per cent in the semi-annihilation region, thus giving credence to the standard approach to the relic density calculation in this regime. In contrast, for dark matter mass just below the Higgs resonance, the modification of the Higgs invisible width and direct and indirect detection signals can be up to a factor $6.7$. The model is then currently allowed at $56.8$ GeV to $58.4$ GeV (depending on the details of early kinetic decoupling) $\lesssim M_{S} \lesssim 62.8$ GeV and at $M_{S} \gtrsim 122$ GeV if the freeze-out is dominated by semi-annihilation. We show that the whole large semi-annihilation region will be probed by the near-future measurements at the XENONnT experiment.