| Summary: | © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has yielded unprecedented measurements of the soft gamma-ray spectrum of our Galaxy. Here we use those measurements to set constraints on dark matter (DM) that decays or annihilates into photons with energies E≈0.02-2 MeV. First, we revisit the constraints on particle DM that decays or annihilates to photon pairs. In particular, for decaying DM, we find that previous limits were overstated by roughly an order of magnitude. Our new, conservative analysis finds that the DM lifetime must satisfy τ≳5×1026 s×(mχ/MeV)-1 for DM masses mχ=0.054-3.6 MeV. For MeV-scale DM that annihilates into photons INTEGRAL sets the strongest constraints to date. Second, we target ultralight primordial black holes (PBHs) through their Hawking radiation. This makes them appear as decaying DM with a photon spectrum peaking at E≈5.77/(8πGMPBH), for a PBH of mass MPBH. We use the INTEGRAL data to demonstrate that, at 95% C.L., PBHs with masses less than 1.2×1017 g cannot comprise all of the DM, setting the tightest bound to date on ultralight PBHs.
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