THESEUS Insights into ALP, Dark Photon and Sterile Neutrino Dark Matter

TL;DR

This paper evaluates the THESEUS mission's instruments for detecting decaying dark matter signals, showing potential to significantly improve existing constraints on axion-like particles, dark photons, and sterile neutrinos.

Contribution

It demonstrates that THESEUS can enhance dark matter parameter constraints by up to 300 times, depending on systematic uncertainties and the specific DM model.

Findings

THESEUS can improve existing dark matter constraints by up to a factor of 300.

Systematic uncertainties of 1% can reduce the constraining power by one to two orders of magnitude.

THESEUS constraints will complement and surpass those of upcoming missions like eXTP and Athena.

Abstract

Through a series of simulated observations, we investigate the capability of the instruments aboard the forthcoming THESEUS mission for the detection of a characteristic signal from decaying dark matter (DM) in the keV-MeV energy range. We focus our studies on three well studied Standard Model extensions hosting axion-like particle, dark photon, and sterile neutrino DM candidates. We show that, due to the sensitivity of THESEUS' X and Gamma Imaging Spectrometer (XGIS) instrument, existing constraints on dark matter parameters can be improved by a factor of up to ~300, depending on the considered DM model and assuming a zero level of systematic uncertainty. We also show that even a minimal level of systematic uncertainty of 1% can impair potential constraints by one to two orders of magnitude. We argue that nonetheless, the constraints imposed by THESEUS will be substantially better than existing ones and will well complement the constraints of upcoming missions such as eXTP and Athena. Ultimately, the limits imposed by THESEUS and future missions will ensure a robust and thorough coverage of the parameter space for decaying DM models, enabling either a detection of dark matter or a significant improvement of relevant limits.