MeV dark matter decay forecasts for the COSI mission

Robin Anthony-Petersen; Orion Ning; Yu Watanabe; Benjamin R. Safdi; Maíra Dutra; Francesca Calore; Savitri Gallego; William Guan; Christopher M. Karwin; Alexander Kusenko; Israel Martinez-Castellanos; Shigeki Matsumoto; Michela Negro; Uwe Oberlack; Field R. Rogers; Thomas Siegert; Tadayuki Takahashi; Haoyu Xie; Hiroki Yoneda; Andreas Zoglauer; Steven E. Boggs; Dieter H. Hartmann; Carolyn A. Kierans; John A. Tomsick

arXiv · 2610.17217

MeV dark matter decay forecasts for the COSI mission

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Abstract

The decay of dark matter (DM) is a generic prediction of many particle physics models, producing distinctive monochromatic signatures in environments such as the Galactic halo. Searches for decaying DM in the elusive 'MeV gap' have remained conspicuously under-explored, despite well-motivated models including axion-like particles, sterile neutrinos, and hidden-sector scenarios predicting signatures in this energy range. The upcoming Compton Spectrometer and Imager (COSI) telescope will help bridge this gap. Designed to probe this energy band with high spectral resolution, low background, and wide field of view, COSI is well-suited for DM line searches at the MeV scale. In this work, we make projections for COSI's 2-year sensitivity for DM decay in the Milky Way halo using dedicated all-sky simulations incorporating COSI's predicted instrument response. We conclude that COSI will improve the sensitivity to the DM lifetime by more than an order of magnitude over the DM mass range 0.4 to 10 MeV.

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Robin Anthony-Petersen, Orion Ning, Yu Watanabe, Benjamin R. Safdi, Maíra Dutra, Francesca Calore, Savitri Gallego, William Guan, Christopher M. Karwin, Alexander Kusenko, Israel Martinez-Castellanos, Shigeki Matsumoto, Michela Negro, Uwe Oberlack, Field R. Rogers, Thomas Siegert, Tadayuki Takahashi, Haoyu Xie, Hiroki Yoneda, Andreas Zoglauer, Steven E. Boggs, Dieter H. Hartmann, Carolyn A. Kierans, John A. Tomsick. 2026-10-12. MeV dark matter decay forecasts for the COSI mission. https://arxiv.org/abs/2610.17217

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