# Flavor constraints on electroweak ALP couplings

## TL;DR

This paper investigates how axion-like particles (ALPs) could influence flavor-changing neutral current processes, providing new insights into their potential signals and constraints within the 0-5 GeV mass range.

## Contribution

It presents the first comprehensive calculation of ALP contributions to FCNC decays considering the most general electroweak couplings at one-loop order.

## Key findings

- $K o ext{pi}
u ar{
u}$ decays set strong limits for invisible ALP channels.
- $B$-meson decays constrain visible ALP decay channels, such as displaced vertices.
- Collider constraints are complementary to flavor-based bounds.

## Abstract

We explore the signals of axion-like particles (ALPs) in flavor-changing neutral current (FCNC) processes. The most general effective linear Lagrangian for ALP couplings to the electroweak bosonic sector is considered, and its contribution to FCNC decays is computed up to one-loop order. The interplay between the different couplings opens new territory for experimental exploration, as analyzed here in the ALP mass range $0<m_a \lesssim 5$ GeV. When kinematically allowed, $K\to \pi \nu \bar{\nu}$ decays provide the most stringent constraints for channels with invisible final states, while $B$-meson decays are more constraining for visible decay channels, such as displaced vertices in $B\to K^{(\ast)} \mu^+ \mu^-$ data. The complementarity with collider constraints is discussed as well.