Anatomy of kaon decays and prospects for lepton flavour universality violation

TL;DR

This paper reviews kaon decay processes, updates Standard Model predictions, explores potential lepton flavour universality violation, and discusses future experimental sensitivities to new physics effects in rare kaon decays.

Contribution

It provides a comprehensive analysis of kaon decay modes, including new theoretical features and the impact of potential BSM effects related to lepton flavour universality violation.

Findings

Updated Standard Model predictions for kaon decays.

Identification of new features in $K_{S,L} o \muar u$ decays.

Analysis of BSM effects with tau and muon Wilson coefficients.

Abstract

The kaon sector is characterised by several processes which are under active investigation across different experiments. In this work, we present the global picture that emerges from a study of the different decay modes. We begin by revisiting the theoretical component of these decays and providing up-to-date predictions of the Standard Model as well as the corresponding uncertainties. Several new features emerge, in particular for $K_{S,L}\to \mu\bar\mu$, and are presented in considerable detail. This offers an ideal platform for extracting the parameter space supported by the existing data. Motivated by possible lepton flavour universality violation in $B$ decays, we investigate such Beyond the Standard Model effects also in rare kaon decays. Without loss of generality, our primary analyses correspond to the paradigm where the Wilson coefficients for operators involving tau leptons are chosen to be equal to that involving the muon, i.e. $\delta C^\tau=\delta C^\mu$. We conclude by presenting the possible picture that can be achieved towards the end of the run of data accumulation in the planned experiments. This includes assumptions on possible sensitivity goals that the experiments can aim to achieve, in order to extract the kind of physics highlighted in this paper.