Nonperturbative improvement of SU(2) lattice gauge theory with adjoint or fundamental flavors

TL;DR

This paper develops a nonperturbative O(a) improvement for SU(2) lattice gauge theory with adjoint and fundamental fermions, reducing lattice artifacts for more precise simulations relevant to technicolor models.

Contribution

It provides the nonperturbative determination of the Sheikholeslami-Wohlert coefficient for improved Wilson fermions in SU(2) gauge theories with adjoint and fundamental flavors.

Findings

Nonperturbative Sheikholeslami-Wohlert coefficient determined

Boundary improvement terms calculated perturbatively

Facilitates more accurate future lattice studies

Abstract

SU(2) gauge theory with two fermions transforming under the adjoint representation may appear conformal or almost conformal in the infrared, and is one of the candidate theories for building models for technicolor. Early lattice Monte Carlo studies of this model have used unimproved Wilson fermion formulation, which can be expected to have large lattice cutoff effects. In this paper we present the calculation of the O(a) improved lattice Wilson-clover action of the theory. The Sheikholeslami-Wohlert coefficient has been determined non-perturbatively, and various boundary improvement terms, needed for the Schroedinger functional formalism, have been calculated in perturbation theory. For comparison, we have also determined the improvement coefficients for SU(2) gauge theory with two fundamental representation fermions. The calculation paves way for more accurate lattice Monte Carlo analyses of the theory in the future.