Low-lying Scalars in an extended Linear $\sigma$ Model

TL;DR

This paper develops an extended linear sigma model incorporating quarkonia, tetraquarks, and glueballs to analyze the mass spectra of low-lying scalar and pseudoscalar mesons, providing insights into their composition and possible glueball candidates.

Contribution

It introduces a comprehensive chiral symmetry-based model that includes quarkonia, tetraquarks, and glueballs, and studies their mass spectra and compositions.

Findings

The model fits the low-lying meson spectra well.

The most glueball-like scalar is likely above 2 GeV.

The pseudoscalar glueball candidate is identified as η(1756).

Abstract

We formulate an extended linear $\sigma$ model of a quarkonia nonet and a tetraquark nonet as well as a complex iso-singlet (glueball) by virtue of chiral symmetry $SU_L(3) \times SU_R(3)$ and $U_A(1)$ symmetry. In the linear realization formalism, we study the mass spectra and components of the low-lying scalars and pseudo scalars in this model. The mass matrices for physical staes are obtained and the glueball candidates are examined. We find that the model can accommodate the mass spectra of low-lying states quite well. Our fits indicate that the most glueball like scalar should be 2 GeV or higher while the glueball pseudoscalar is $\eta(1756)$. We also examine the parameter region where the lightest iso-scalar $f_0(600)$ can be the glueball and quarkonia dominant but find such a parameter region may be confronted with the problem of the unbounded vacuum from below.