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General relativistic effects on photon spectrum emitted from dark matter halos around primordial black holes

Toya Suzuki1,2,*, Takahisa Igata3,†, Kazunori Kohri1,2,4,5,‡, and Tomohiro Harada6,§

  • *Contact author: toya.suzuki@grad.nao.ac.jp
  • †Contact author: takahisa.igata@gakushuin.ac.jp
  • ‡Contact author: kazunori.kohri@gmail.com
  • §Contact author: harada@rikkyo.ac.jp
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Phys. Rev. D 112, 023501 – Published 1 July, 2025

DOI: https://doi.org/10.1103/vjp4-2pty

Abstract

We investigate general relativistic effects on the photon spectrum emitted from decaying (or annihilating) particle dark matter in the halo surrounding a primordial black hole. The spectrum undergoes significant modification due to gravitational redshifts, which induces broadening as a result of the intense gravitational field near the black hole. This characteristic alteration in the photon spectrum presents a unique observational signature. Future observations of such spectral features may provide critical evidence for a mixed dark matter scenario, involving both primordial black holes and particle dark matter.

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Phys. Rev. D 112, 023501– Published 1 July, 2025
  • Received 11 April 2025
  • Accepted 9 June 2025
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