Limits on ALP-neutrino couplings from loop-level processes

Abstract

We obtain new bounds on effective ALP-neutrino interactions from their loop-level impact on the ALP couplings to electroweak gauge bosons $\gamma Z$, $ZZ$ and $W^+W^-$. Both types of interactions are connected via the chiral anomaly, which allows to overcome the fermion mass suppression of tree-level analyses. ALP couplings to charged leptons are considered simultaneously with ALP-neutrino ones, as required by gauge invariance. Complete one-loop computations are presented together with relevant kinematic limits. We leverage data obtained from rare meson decay measurements alongside observations from collider experiments, among others. The novel constraints are particularly competitive for ALP masses $\gtrsim 100$ MeV, evidencing the powerful potential of future ALP searches at colliders which target its couplings to electroweak gauge bosons.