Chimera baryons and mesons on the lattice: a spectral density analysis

TL;DR

This paper introduces a spectral-density analysis method for lattice field theory, applying it to a specific gauge theory to extract masses and matrix elements of mesons and chimera baryons, relevant for composite Higgs models.

Contribution

It develops a novel spectral-density analysis technique with smeared energy kernels and applies it to a complex gauge theory, providing first measurements of chimera baryon states with dynamical fermions.

Findings

First measurements of chimera baryon ground and excited states with dynamical fermions.

New results on meson decay constants and matrix elements.

Updated meson mass measurements with higher statistics.

Abstract

We develop and test a spectral-density analysis method, based on the introduction of smeared energy kernels, to extract physical information from two-point correlation functions computed numerically in lattice field theory. We apply it to a $Sp(4)$ gauge theory and fermion matter fields transforming in distinct representations, with $N_{\rm f}=2$ Dirac fermions in the fundamental and $N_{\rm as}=3$ in the 2-index antisymmetric representation. The corresponding continuum theory provides the minimal candidate model for a composite Higgs boson with partial top compositeness. We consider a broad class of composite operators, that source flavored mesons and (chimera) baryons, for several finite choices of lattice bare parameters. For the chimera baryons, which include candidate top-quark partners, we provide the first measurements, obtained with dynamical fermions, of the ground state and the lowest excited state masses, in all channels of spin, isospin, and parity. We also measure matrix elements and overlap factors, that are important to realize viable models of partial top compositeness, by implementing an innovative way of extracting this information from the spectral densities. For the mesons, among which the pseudoscalars can be reinterpreted to provide an extension of the Higgs sector of the Standard Model of particle physics, our measurements of the renormalized matrix elements and decay constants are new results. We complement them with an update of existing measurements of the meson masses, obtained with higher statistics and improved analysis. The analysis software is made publicly available, and can be used in other lattice studies, including application to quantum chromodynamics (QCD).