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Constraints on millicharged particles from nuclear γ-decays

Ting Gao1,* and Maxim Pospelov1,2,†

  • 1School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
  • 2William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA

  • *Contact author: gao00212@umn.edu
  • †Contact author: pospelov@umn.edu
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Phys. Rev. D 113, 115044 – Published 17 June, 2026

DOI: https://doi.org/10.1103/ys3l-3bcd

Abstract

We consider nuclear gamma decays and γ-emitting reactions that can be an efficient source of hypothetical millicharged particles (χ). In particular, we revisit the production of millicharged particles in nuclear reactor environment, pointing out that γ cascades from U239 is an overlooked yet a powerful source of χχ¯ pairs. This leads to an increased flux compared to previous studies. We then apply new estimates of the flux to derive novel limits on the value of millicharge, ϵ=Qχ/e, from the electron recoil searched for in a variety of experiments placed in proximity to the reactor cores. The derived limits on ϵ are the strongest in the interval of masses ∼0.7–2  MeV. We also derive the millicharged particles flux from the Sun and point out potential sensitivity of the low-threshold dark matter search experiments.

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Phys. Rev. D 113, 115044– Published 17 June, 2026
  • Received 19 November 2025
  • Accepted 19 May 2026
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Published by the American Physical Society under the terms of the 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. Funded by SCOAP3.

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