Lattice studies of chimera baryons in Sp(4) gauge theory

Abstract

We study chimera baryons, fermion bound states composed of two (hyper)quarks transforming in the fundamental and one in the antisymmetric representation of a non-Abelian gauge group. While in QCD they coincide with ordinary baryons, in composite Higgs models (CHMs) with top partial compositeness, spin-1/2 chimera baryons serve as partners of the top quark and are responsible for its large mass. We perform non-perturbative lattice calculations of the low-lying spectrum of the chimera baryons, in a specific realization of CHMs based on a Sp(4) gauge theory. In the quenched approximation, we present the numerical results in the continuum and massless limits. Then, for dynamical fermions, we measure the spectrum and matrix elements by employing a newly developed spectral density analysis for several choices of the lattice parameters.

Figures (4)

• Figure 1: Continuum-extrapolated masses taken from Ref. Bennett:2023mhh, for (parity-even) chimera baryons, $\Lambda_{\rm CB}$, $\Sigma_{\rm CB}$, and $\Sigma^*_{\rm CB}$ in the quenched Sp$(4)$ gauge theory, as a function of the mass squared, $\hat{m}_{\rm PS}^2$ (left) and $\hat{m}_{\rm ps}^2$ (right), of mesons composed of $({\rm f})$- and $({\rm as})$-type hyperquark constituents.
• Figure 2: Summary plot for the mass spectrum in the quenched approximation for the ${\rm Sp}(4)$ gauge theory, extrapolated to the continuum and massless-hyperquark limits Bennett:2023mhh. We denote mesons composed of $(f)$-type ($(as)$-type) hyperquarks as PS (ps), V (v), T (t), AV (av), AT (at), S (s), according to the gamma-matrix structure of the corresponding hyperquark bilinear operator Bennett:2019cxd. We also show the glueball states, identified by their spin and parity quantum numbers, $J^P$Bennett:2020qtj.
• Figure 3: Summary plot for the mass spectrum of the ${\rm Sp}(4)$ gauge theory coupled to dynamical hyperquarks in the fundamental and antisymmetric representations TELOS:2025ash. The ensembles M1 to M5 are characterised by different choices of lattice parameters, as discussed in the main text. The identifications of mesons and chimera baryons use the same conventions as in Fig. \ref{['fig:fig_qc_spec']}, with additional notation for parity-even (+) and parity-odd (-) chimera baryons.
• Figure 4: Renormalised overlap factors of chimera baryons in the ${\rm Sp}(4)$ gauge theory coupled to dynamical hyperquarks in the fundamental and antisymmetric representations TELOS:2025ash.