The running coupling from gluon and ghost propagators in the Landau gauge: Yang-Mills theories with adjoint fermions

TL;DR

This study investigates how the running coupling in SU(2) gauge theories with adjoint fermions varies with the number of fermions, using lattice simulations of ghost and gluon propagators in the Landau gauge.

Contribution

It provides the first lattice analysis of the running coupling in adjoint QCD with varying fermion numbers approaching the conformal window.

Findings

The running coupling behavior changes as the number of fermions increases.

Evidence of the transition towards conformal behavior with more fermions.

Lattice results support theoretical expectations for the conformal window.

Abstract

Non-Abelian gauge theories with fermions transforming in the adjoint representation of the gauge group (AdjQCD) are a fundamental ingredient of many models that describe the physics beyond the Standard Model. Two relevant examples are N=1 Supersymmetric Yang-Mills (SYM) theory and Minimal Walking Technicolor, which are gauge theories coupled to one adjoint Majorana and two adjoint Dirac fermions, respectively. While confinement is a property of N=1 SYM, Minimal Walking Technicolor is expected to be infrared conformal. We study the propagators of ghost and gluon fields in the Landau gauge to compute the running coupling in the MiniMom scheme. We analyze several different ensembles of lattice Monte Carlo simulations for the SU(2) adjoint QCD with Nf=1/2, 1, 3/2, and 2 Dirac fermions. We show how the running of the coupling changes as the number of interacting fermions is increased towards the conformal window.