Neutral kaon mixing beyond the standard model with nf=2+1 chiral fermions

TL;DR

This study calculates hadronic matrix elements for neutral kaon mixing beyond the Standard Model using nf=2+1 domain-wall fermions, providing non-perturbative renormalization and systematic error analysis.

Contribution

It presents the first unquenched calculation of these matrix elements with good chiral symmetry and non-perturbative renormalization, extending previous quenched results.

Findings

Large ratios of non-SM to SM matrix elements confirmed

Systematic errors including discretisation effects estimated

Results consistent with previous quenched studies

Abstract

We compute the hadronic matrix elements of the four-quark operators needed for the study of neutral kaon mixing beyond the Standard Model (SM). We use nf=2+1 flavours of domain-wall fermions (DWF) which exhibit good chiral-flavour symmetry. The renormalization is performed non-perturbatively through the RI-MOM scheme and our results are converted perturbatively to MSbar. The computation is performed on a single lattice spacing a=0.086 fm with a lightest unitary pion mass of 290 MeV. The various systematic errors, including the discretisation effects, are estimated and discussed. Our results confirm a previous quenched study, where large ratios of non-SM to SM matrix elements were obtained.