Kaon Mixing Beyond the Standard Model

TL;DR

This paper presents a lattice QCD calculation of hadronic matrix elements relevant for K-Kbar mixing in BSM theories, aiming to resolve discrepancies and improve precision using domain wall fermions at two lattice spacings.

Contribution

It extends previous work by including a second lattice spacing and employs non-perturbative renormalization to enhance the accuracy of matrix element calculations.

Findings

Discrepancies with previous results highlight the need for uncertainty reduction.

Use of multiple lattice spacings improves the robustness of the results.

Non-perturbative renormalization enhances the reliability of matrix element estimates.

Abstract

We report on an ongoing calculation of hadronic matrix elements needed to parameterize K-Kbar mixing in generic BSM scenarios, using domain wall fermions (DWF) at two lattice spacings. Recent work by the SWME collaboration shows a significant disagreement with our previous results for two of these quantities. Since the origin of this disagreement is unknown, it is important to reduce the various uncertainties. In this work, we are using N_f=2+1 DWF with Iwasaki gauge action at inverse lattice spacings of 2.31 and 1.75 GeV, with multiple unitary pions on each ensemble, the lightest being 290 and 330 MeV on the finer and coarser of the two ensembles respectively. This extends previous work by the addition of a second lattice spacing (a^{-1}\approx 1.75 GeV). Renormalization is carried out non-perturbatively in the RI/MOM scheme and converted perturbatively to MSbar.