The running of the bare coupling in SU(N) gauge theories

TL;DR

This paper investigates the running of the bare coupling in SU(N) gauge theories, demonstrating that the string tension fits perturbative expressions with lattice corrections and comparing coupling schemes to identify the most accurate one.

Contribution

It provides a detailed analysis of the bare coupling's behavior in SU(N) gauge theories and compares different schemes, especially in SU(3), to determine the most reliable for continuum extrapolation.

Findings

String tension fits well with 3-loop perturbative expressions with lattice corrections.

The Parisi mean-field improved coupling scheme aligns closely with the Schrödinger Functional scheme.

Derived a formula for Lambda_MSbar/sqrt(sigma) as a function of N with statistical and systematic errors.

Abstract

For N>4 there is a first order bulk transition that cleanly separates the strong and weak coupling regimes of SU(N) lattice gauge theories with the plaquette action. We find that in this case the calculated string tension can be readily fitted throughout the weak coupling region by a standard 3-loop perturbative expression modified by lattice spacing corrections of the expected form. While our fits demand the presence of the latter, they are not constraining enough to tell us which of the various bare coupling schemes is a `good' one, in the sense that terms in the beta-function beyond 3-loops are indeed negligible (in the relevant range of scales). To resolve this ambiguity we work in SU(3), using the Schrodinger Functional coupling scheme as a benchmark, and find that the Parisi mean-field improved coupling scheme matches it very well. Using the latter scheme, we have fitted the values of the string tension that have been calculated for SU(3) to SU(8), to obtain Lambda_MSbar/sqrt(sigma) = 0.503(2)(40) + 0.33(3)(3)/N**2, where the first error is statistical and the second is our estimate of the systematic error from all sources.