2026/02/23 by Matheus Hostert, Maxim Pospelov, Adrian Thompson · 1 voice
#hep-ph #hep-ex
We study rare three- and four-body kaon decays as a probe of light vector and axial-vector bosons coupled to non-conserved currents. We find that searches for KL → π0 π0 (X→ 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+ → π+ π0 (X → e+e-) and KL → π+ π- (X → 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 → πXX decays can provide yet additional constraints on the parameter space of light X bosons due to a double (mK/mX)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.