$\gamma_5$ in dimensional regularization -- a no-compromise approach using the BMHV scheme

TL;DR

This paper discusses the BMHV scheme for defining $oldsymbol{ extgamma_5}$ in dimensional regularization, focusing on restoring gauge invariance in chiral gauge theories through finite counterterms, with explicit 2-loop results.

Contribution

It introduces a method to identify finite counterterms needed to restore gauge invariance in the BMHV scheme at the 2-loop level.

Findings

Three types of symmetry-restoring counterterms are sufficient at 2-loop level.

The results are notably simple and manageable.

The approach facilitates applications and cross-checks of regularization schemes.

Abstract

$\gamma_5$ is notoriously difficult to define in $D$ dimensions. The traditional BMHV scheme employs a non-anticommuting $\gamma_5$. Its key advantage is mathematical consistency and the existence of all-order proofs. Its disadvantage is the spurious breaking of gauge invariance in chiral gauge theories like the electroweak standard model. Our research programme aims to determine the special finite counterterms which are necessary to restore gauge invariance, to allow more straightforward applications of the BMHV scheme and to cross-check alternative schemes. In these proceedings we present the key concepts and methods, and we outline the calculational procedure and present results for an abelian gauge theory at the 2-loop level. An important observation is the simplicity of the results -- three types of symmetry-restoring counterterms are sufficient at the 2-loop level.