Limits from the grave: resurrecting Hitomi for decaying dark matter and forecasting leading sensitivity for XRISM

TL;DR

This paper enhances the search for decaying dark matter using archival Hitomi data and forecasts XRISM's future sensitivity, highlighting potential breakthroughs in detecting sterile neutrinos and axion-like particles in the 1-20 keV range.

Contribution

It presents the first improved analysis of archival Hitomi data for dark matter decay and projects XRISM's leading future sensitivity in this energy range.

Findings

Archival Hitomi data provides improved constraints on decaying dark matter.

XRISM will have the highest sensitivity for dark matter masses between 1 and 20 keV.

Implications for sterile neutrino and axion-like particle dark matter models.

Abstract

The Hitomi X-ray satellite mission carried unique high-resolution spectrometers that were set to revolutionize the search for sterile neutrino dark matter (DM) by looking for narrow X-ray lines arising from DM decays. Unfortunately, the satellite was lost shortly after launch, and to-date the only analysis using Hitomi for DM decay used data taken towards the Perseus cluster. In this work we present a significantly more sensitive search from an analysis of archival Hitomi data towards blank sky locations, searching for DM decaying in our own Milky Way. The soon-to-be-launched XRISM satellite will have nearly identical soft-X-ray spectral capabilities to Hitomi; we project the full-mission sensitivity of XRISM for analyses of their future blank-sky data, and we find that XRISM will have the leading sensitivity to decaying DM for masses between roughly 1 to 20 keV, with important implications for sterile neutrino and heavy axion-like particle DM scenarios.