Limits on ALP-neutrino couplings from loop-level processes

TL;DR

This paper derives new bounds on axion-like particle (ALP) interactions with neutrinos by analyzing their loop effects on gauge boson couplings, using experimental data from meson decays and colliders.

Contribution

It provides the first complete one-loop calculations connecting ALP-neutrino and gauge boson couplings, improving constraints especially for ALP masses above 100 MeV.

Findings

New bounds on ALP-neutrino interactions from loop effects.

Constraints are competitive for ALP masses > 100 MeV.

Future collider searches can significantly improve these bounds.

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.