A light composite scalar in eight-flavor QCD on the lattice

TL;DR

This study reports the first lattice simulation evidence of a light flavor-singlet scalar in eight-flavor QCD, a candidate for walking technicolor, with a mass comparable to the pion across different fermion masses.

Contribution

The paper presents the first observation of a light scalar meson in eight-flavor QCD using lattice simulations, supporting its potential as a composite Higgs candidate.

Findings

Evidence of a flavor-singlet scalar with mass similar to the pion.

Scalar mass remains small compared to the vector meson.

Scalar mass behavior consistent across different fermion masses.

Abstract

In search for a composite Higgs boson (techni-dilaton) in the walking technicolor, we present our preliminary results on the first observation of a light flavor-singlet scalar in a candidate theory for the walking technicolor, the Nf=8 QCD, which was found in our previous paper to have spontaneous chiral symmetry breaking together with remnants of the conformality. Based on simulations with the HISQ-type action on several lattice sizes with various fermion masses, we find evidence of a flavor-singlet scalar meson with mass comparable to that of the Nambu-Goldstone pion in both the small fermion-mass region, where chiral perturbation theory works, and the intermediate fermion-mass region where the hyperscaling relation holds. We further discuss its chiral limit extrapolation in comparison with other states studied in our previous paper: the scalar has a mass much smaller than that of the vector meson, which is compared to the Nambu-Goldstone pion having a vanishing mass in that limit.