QED corrections to bound-muon decays from an effective-field-theory framework

TL;DR

This paper develops an effective-field-theory framework to systematically compute QED corrections in bound-muon decays, improving the precision of spectral predictions crucial for new physics searches.

Contribution

It introduces a universal EFT approach for calculating QED corrections in bound-muon decays, providing the most accurate spectra predictions to date.

Findings

Radiative corrections alter the leading-order spectrum ratio by 5%.

The corrections show minimal energy dependence.

Framework advances the connection between high-energy physics and low-energy observables.

Abstract

Bound-muon decays are a powerful probe of new physics, making precise theoretical predictions for their spectra essential. While QED corrections significantly affect the shape of the spectra, their calculation is extremely challenging below the nuclear scale. By exploring the universality of modern effective-field-theory techniques, we present a framework that systematically computes those corrections across a broad class of bound-muon decays. As a key application, we provide the most accurate predictions to date for the signal and background spectra in muon conversion. We show that radiative corrections modify the leading-order ratio of these spectra by $5\%$ with minimal energy dependence, a result relevant for enhancing the discovery reach of upcoming experiments. Our framework also represents a crucial step toward connecting high-energy physics to low-energy observables, complementing recent progress above the muon mass scale.