New calculations of neutron and kaon decays

TL;DR

This paper presents improved theoretical calculations of radiative corrections in neutron and kaon decays, refining the values of CKM matrix elements and potentially indicating new physics beyond the Standard Model.

Contribution

It introduces a novel dispersive analysis for the neutron gamma-W box diagram and combines multiple theoretical approaches for kaon decay corrections, enhancing precision and understanding.

Findings

Refined value of V_{ud} with reduced uncertainty

Improved determination of radiative corrections in kaon decays

Potential implications for new physics due to anomalies in CKM measurements

Abstract

We describe two recent developments of the radiative correction theory in semileptonic beta decays. For neutron, a novel dispersive analysis of the $\gamma W$-box diagram making use of neutrino scattering data leads to an improved precision and a shifted central value of $V_{ud}$; for kaon, an appropriate combination of meson form factors, lattice QCD inputs and chiral perturbation theory gives a much-improved determination of the radiative corrections in semileptonic kaon decays. These new calculations help to unveil/sharpen a series of anomalies in the measurements of $V_{ud}$ and $V_{us}$ that may point towards the existence of new physics.