Consistent treatment of axions in the weak chiral Lagrangian

TL;DR

This paper develops a consistent method for including axions in weak decay processes within chiral Lagrangian theory, correcting previous inaccuracies and providing new, more precise predictions for specific decay rates.

Contribution

It introduces a correct representation of flavor-changing quark currents in the chiral framework for axion-related weak decays, improving upon prior approaches.

Findings

The $K^- o ext{pi}^- a$ branching ratio is nearly 40 times larger than earlier estimates.

Derived model-independent decay results at leading order for arbitrary axion couplings and masses.

Provided a consistent theoretical framework for axion-involved weak decays in chiral perturbation theory.

Abstract

We present a consistent implementation of weak decays involving an axion or axion-like particle in the context of an effective chiral Lagrangian. We argue that previous treatments of such processes have used an incorrect representation of the flavor-changing quark currents in the chiral theory. As an application, we derive model-independent results for the decays $K^-\to\pi^- a$ and $\pi^-\to e^-\bar\nu_e a$ at leading order in the chiral expansion and for arbitrary axion couplings and mass. In particular, we find that the $K^-\to\pi^- a$ branching ratio is almost 40 times larger than previously estimated.