Spectroscopy of the BSM sextet model

Zoltan Fodor,Daniel Nogradi,Kieran Holland,Chik Him Wong,Julius Kuti,M Della Morte,P Fritzsch,E Gámiz Sánchez,C Pena Ruano

doi:10.1051/epjconf/201817508014

Abstract

As part of our ongoing lattice study of SU(3) gauge theory with two flavors of fermions in the two-index symmetric representation (the sextet model), we present the current status of the pseudoscalar particle spectrum. We use a mixed action approach based on the gradient flow to control lattice artifacts, allowing a simultaneous extrapolation to the chiral and continuum limits. We find strong evidence that the pseudoscalar is a Goldstone boson state, with spontaneously broken chiral symmetry and a non-zero Goldstone decay constant in the chiral limit. In agreement with our study of the gauge coupling β function, we find the sextet model appears to be a near-conformal gauge theory and serves as a prototype of the composite Higgs BSM template.

Highlights

If physics beyond the Standard Model (BSM) is realized by a strongly-interacting gauge theory with new fermionic degrees of freedom, one of the fundamental questions will be what kind of particle spectrum such a theory produces [1]
The model is economic with few new degrees of freedom and if spontaneous chiral symmetry breaking occurs, the three Goldstone bosons exactly match the longitudinal modes of the Electroweak gauge
The scale t0/a2 is set implicitly by the choice of renormalized coupling, we find g2(t0) = 6.7 is convenient for the lattice volumes and spacings we have used. (Note that this does not correspond to the choice of t0 set by t2 · E t0 = 0.3 in the original investigation of [11].) We will later use the scale t0 to fit the O(a2) lattice artifacts in the spectrum, similar to the fitting of lattice artifacts in the infinite volume β function in [16]

Summary

Introduction

If physics beyond the Standard Model (BSM) is realized by a strongly-interacting gauge theory with new fermionic degrees of freedom, one of the fundamental questions will be what kind of particle spectrum such a theory produces [1]. It is important to study ab initio the particle spectrum of a proposed model using lattice simulations, since a theory may be infrared conformal with no massive particle states in the massless fermion limit. Coupling such a theory to the Standard Model would not break electroweak symmetry in the standard way. Our initial lattice studies of the particle spectrum indicate that χSB does take place [3, 5, 6] This complements our other non-perturbative work which shows that the β function of the theory is small but non-zero, consistent with a walking theory [4]. We have continued our investigation of the particle spectrum, we present here an update for the Goldstone states and their chiral analysis

Improvement

Chiral and continuum limits

F π2 F 1

Comparison and conclusion