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Improved constraints on exotic electron-proton interactions in hydrogen

Lei Cong1,2,3, Filip Ficek4,5, Pavel Fadeev3, and Dmitry Budker1,2,3,6,*

  • *Contact author: budker@uni-mainz.de
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Phys. Rev. A 112, 052824 – Published 20 November, 2025

DOI: https://doi.org/10.1103/8nyk-sysy

Abstract

Atomic spectroscopy provides a sensitive tool for searching for new bosons that mediate exotic forces between elementary fermions. A comparison between a recent high-precision measurement [Bullis et al., Phys. Rev. Lett. 130, 203001 (2023)] of the hyperfine splitting of the 2S1/2 electronic level in hydrogen and up-to-date bound-state quantum electrodynamics calculations yields improved constraints on electron-proton exotic interactions. These are expressed in terms of the dimensionless coupling strengths gAgA, gpgp, and gVgV, corresponding to the exchange of axial-vector, pseudoscalar (axionlike), and vector bosons, respectively. Building on these results, our analysis highlights the importance of examining combinations of spin-dependent potentials that contribute to the same class of exotic interactions. In particular, we employ the combination V2+V3 for both axial-vector–axial-vector and vector-vector couplings. These findings motivate further precision measurements toward spin-dependent exotic interactions.

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Phys. Rev. A 112, 052824– Published 20 November, 2025
  • Received 28 May 2025
  • Accepted 17 October 2025
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