Low-energy signals from the formation of dark-matter-nucleus bound states

Asher Berlin, Hongwan Liu, Maxim Pospelov, Harikrishnan Ramani

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2 Scopus citations


Dark matter particles may bind with nuclei if there exists an attractive force of sufficient strength. We show that a dark photon mediator of mass ∼(10-100) MeV that kinetically mixes with Standard Model electromagnetism at the level of ∼10-3 generates keV-scale binding energies between dark matter and heavy elements, while forbidding the ability to bind with light elements. In underground direct detection experiments, the formation of such bound states liberates keV-scale energy in the form of electrons and photons, giving rise to monoenergetic electronic signals with a time structure that may contain daily and seasonal modulations. We show that data from liquid-xenon detectors provides exquisite sensitivity to this scenario, constraining the galactic abundance of such dark particles to be at most ∼10-18-10-12 of the galactic dark-matter density for masses spanning ∼(1-105) GeV. However, an exponentially small fractional abundance of these dark particles is enough to explain the observed electron recoil excess at XENON1T.

Original languageEnglish (US)
Article number095028
JournalPhysical Review D
Issue number9
StatePublished - May 1 2022
Externally publishedYes

Bibliographical note

Funding Information:
The authors would like to acknowledge Carlos Blanco, Oren Slone, and Neal Weiner for fruitful conversations. A. B. is supported by the James Arthur Fellowship. H. L. is supported by the DOE under Award No. DE-SC0007968, NSF Grant No. PHY-1915409, and the Simons Foundation. M. P. is supported in part by U.S. Department of Energy (Grant No. DE-SC0011842). H. R. is supported in part by NSF Grant No. PHY-1720397 and the Gordon and Betty Moore Foundation Grant No. GBMF7946.

Publisher Copyright:
© 2022 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. Funded by SCOAP3.


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