Lattice investigations of the chimera baryon spectrum in the Sp(4) gauge theory

TL;DR

This study uses lattice simulations to investigate the spectrum of chimera baryons in an Sp(4) gauge theory, relevant for composite Higgs models, focusing on the lightest states and their potential as top-quark partners.

Contribution

First non-perturbative lattice analysis of chimera baryon spectrum in Sp(4) gauge theory, exploring candidates for top partners in composite Higgs models.

Findings

$ ext{Sigma}_{ ext{CB}}$ is not heavier than $ ext{Lambda}_{ ext{CB}}$ within simulated mass range.

Spectrum extrapolated using QCD-inspired chiral perturbation theory.

Focus on three lightest parity-even chimera-baryon states, including spin 1/2 and 3/2 states.

Abstract

We report the results of lattice numerical studies of the Sp(4) gauge theory coupled to fermions (hyperquarks) transforming in the fundamental and two-index antisymmetric representations of the gauge group. This strongly-coupled theory is the minimal candidate for the ultraviolet completion of composite Higgs models that facilitate the mechanism of partial compositeness for generating the top-quark mass. We measure the spectrum of the low-lying, half-integer spin, bound states composed of two fundamental and one antisymmetric hyperquarks, dubbed chimera baryons, in the quenched approximation. In this first systematic, non-perturbative study, we focus on the three lightest parity-even chimera-baryon states, in analogy with QCD, denoted as $\Lambda_{\rm CB}$, $\Sigma_{\rm CB}$ (both with spin 1/2), and $\Sigma_{\rm CB}^\ast$(with spin 3/2). The spin-1/2 such states are candidates of the top partners. The extrapolation of our results to the continuum and massless-hyperquark limit is performed using formulae inspired by QCD heavy-baryon Wilson chiral perturbation theory. Within the range of hyperquark masses in our simulations, we find that $\Sigma_{\mathrm{CB}}$ is not heavier than $\Lambda_{\mathrm{CB}}$.