The running coupling of the minimal sextet composite Higgs model

TL;DR

This study non-perturbatively computes the running coupling in a minimal sextet composite Higgs model using lattice simulations, finding no infrared fixed point within the explored coupling range, thus informing beyond Standard Model theories.

Contribution

First continuum non-perturbative calculation of the running coupling in the minimal sextet composite Higgs model using gradient flow on the lattice.

Findings

Results agree with perturbation theory at small couplings.

Observed a downward deviation from 2-loop beta-function at moderate couplings.

No infrared fixed point detected in the explored coupling range.

Abstract

We compute the renormalized running coupling of SU(3) gauge theory coupled to N_f = 2 flavors of massless Dirac fermions in the 2-index-symmetric (sextet) representation. This model is of particular interest as a minimal realization of the strongly interacting composite Higgs scenario. A recently proposed finite volume gradient flow scheme is used. The calculations are performed at several lattice spacings with two different implementations of the gradient flow allowing for a controlled continuum extrapolation and particular attention is paid to estimating the systematic uncertainties. For small values of the renormalized coupling our results for the beta-function agree with perturbation theory. For moderate couplings we observe a downward deviation relative to the 2-loop beta-function but in the coupling range where the continuum extrapolation is fully under control we do not observe an infrared fixed point. The explored range includes the locations of the zero of the 3-loop and the 4-loop beta-functions in the MSbar scheme. The absence of a non-trivial zero in the beta-function in the explored range of the coupling is consistent with our earlier findings based on hadronic observables, the chiral condensate and the GMOR relation. The present work is the first to report continuum non-perturbative results for the sextet model.