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Kaon decay constraints on vector bosons coupled to nonconserved currents

Matheus Hostert ^1,*, Maxim Pospelov^2,3,†, and Adrian Thompson ^4,‡

¹Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
²School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
³William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
⁴Department of Physics & Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA

^*Contact author: matheus-hostert@uiowa.edu
^†Contact author: pospelov@umn.edu
^‡Contact author: a.thompson@northwestern.edu

Phys. Rev. D 113, 115003 – Published 2 June, 2026

DOI: https://doi.org/10.1103/wvhd-8mtc

Abstract

We study rare three- and four-body kaon decays as a probe of light vector and axial-vector bosons coupled to nonconserved currents. We find that searches for $K_{L} \to π^{0} π^{0} (X \to e^{+} e^{-})$ decays constrain the couplings of light $X$ bosons to light quarks to be as small as $O (10^{- 5})$ . The charged-pion modes $K^{+} \to π^{+} π^{0} (X \to e^{+} e^{-})$ and $K_{L} \to π^{+} π^{-} (X \to e^{+} e^{-})$ provide weaker limits, but constrain complementary combinations of couplings to the $u$ , $d$ , and $s$ quarks at the level of $O (10^{- 4})$ . Finally, we also find that double emission of $X$ in $K \to π X X$ decays can provide yet additional constraints on the parameter space of light $X$ bosons due to a double $(m_{K} / m_{X})^{2}$ enhancement to the rate. For a 17 MeV boson, these limits add to the known tension between spin-1 bosons coupled to vector and axial-vector currents interpretations of the results of the ATOMKI experiment with meson decay data. Finally, we also comment on negative pion capture on hydrogen and deuterium as a source of light particles and discuss the prospects for testing the 17 MeV boson hypothesis.

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Phys. Rev. D 113, 115003– Published 2 June, 2026

Vol. 113, Iss. 11 — 1 June 2026

Received 17 March 2026
Accepted 16 April 2026

DOI: https://doi.org/10.1103/wvhd-8mtc

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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Kaon decay constraints on vector bosons coupled to nonconserved currents

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