Kaon leptonic and semileptonic decays with $N_f=2+1+1$ HISQ fermions

TL;DR

This paper reports progress in lattice QCD calculations of kaon decays using HISQ fermions, aiming to improve tests of CKM unitarity by analyzing decay constants and form factors with chiral perturbation theory guidance.

Contribution

It introduces a new analysis framework for kaon decay data using HISQ configurations and chiral perturbation theory to enhance precision in CKM unitarity tests.

Findings

Progress in lattice-QCD calculations of kaon decay constants and form factors.

Implementation of chiral-continuum fits guided by SChPT.

Initial results showing improved correlations and data analysis methods.

Abstract

Precision tests of the Standard Model (SM) currently show a deficit in first-row Cabibbo-Kobayashi-Maskawa (CKM) unitarity. In this talk, we discuss progress towards a correlated analysis of the lattice-QCD inputs needed to test this relation with kaon data using highly improved staggered quarks (HISQ) on the MILC $N_{f}=2+1+1$ configurations. We present the status of a new analysis of light-meson decay constant data where chiral-continuum fits are guided by staggered chiral perturbation theory (SChPT). The goal of SChPT is twofold: it allows us to use data not only at physical pion mass but also at unphysical masses. Moreover, it provides values of ChPT low energy constants (LECs) as well as their correlations. We also present a reanalysis of our previous kaon semileptonic form factor calculation, aiming to estimate correlations between the form factor and light-meson decay constants. We discuss the new methodology, new data included, and present some preliminary results.