SU(3)-breaking effects in kaon and hyperon semileptonic decays from lattice QCD

TL;DR

This paper reports a high-precision lattice QCD calculation of the kaon to pion vector form factor at zero momentum transfer, which impacts the determination of the CKM matrix element |V_us| and includes preliminary hyperon decay results.

Contribution

It provides a quenched lattice QCD calculation of f+(0) with percent-level accuracy and explores hyperon decay form factors using a similar approach.

Findings

f+(0) = 0.960 ± 0.005_stat ± 0.007_syst, consistent with previous estimates.

Updated |V_us| extraction using the new lattice result and recent experimental data.

Initial lattice study of hyperon Sigma -> n l nu decays with promising results.

Abstract

We discuss the result of a recent quenched lattice calculation of the K -> pi vector form factor at zero-momentum transfer, relevant for the determination of |V_us| from K-> pi l nu decays. Using suitable double ratios of three-point correlation functions, we show that it is possible to calculate this quantity at the percent-level precision. The leading quenched effects are corrected for by means of quenched chiral perturbation theory. The final result, f+(0) = 0.960 +- 0.005_stat +- 0.007_syst, turns out to be in good agreement with the old quark model estimate made by Leutwyler and Roos. In this paper, we discuss the phenomenological impact of the lattice result for the extraction of |V_us|, by updating the analysis of K -> pi l nu decays with the most recent experimental data. We also present a preliminary lattice study of hyperon Sigma -> n l nu decays, based on a similar strategy.