$\chi$SF near the electroweak scale

TL;DR

This paper uses the chirally rotated Schr"odinger functional to study fermion bilinear correlations for renormalization, providing preliminary tuning results and comparing with perturbation theory, with implications for computing $B_K$ matrix elements.

Contribution

It introduces a novel application of the $ ext{chi}$SF to determine renormalization constants and improve $B_K$ calculations, including BSM contributions, at the electroweak scale.

Findings

Preliminary tuning of $z_f$ and $Z_A$ shown.

Comparison with one-loop perturbation theory conducted.

Framework for automatic $ ext{O}(a)$-improved $B_K$ computation outlined.

Abstract

We employ the chirally rotated Schr\"odinger functional ($\chi$SF) to study two-point fermion bilinear correlation functions used in the determination of $Z_{A,V,S,P,T}$ on a series of well-tuned ensembles. The gauge configurations, which span renormalisation scales from 4 to 70~GeV, are generated with $N_{\rm f}=3$ massless flavors and Schr\"odinger Functional (SF) boundary conditions. Valence quarks are computed with $\chi$SF boundary conditions. We show preliminary results on the tuning of the $\chi$SF Symanzik coefficient $z_f$ and the scaling of the axial current normalization $Z_{\rm A}$. Moreover we carry out a detailed comparison with the expectations from one-loop perturbation theory. Finally we outline how automatically $\mathrm{O}(a)$-improved $B_{\rm K}$ matrix elements, including BSM contributions, can be computed in a $\chi$SF renormalization scheme.