Role of the tetraquark in the chiral phase transition

TL;DR

This paper explores how tetraquark fields influence chiral symmetry restoration at finite temperature, revealing a strong mixing with quarkonium states that affects the mass spectrum and the nature of the phase transition.

Contribution

It demonstrates that a significant mixing between tetraquark and quarkonium fields is essential for a crossover chiral phase transition, providing a new perspective on the scalar meson spectrum and chiral dynamics.

Findings

Identification of a light tetraquark-dominated state (~0.4 GeV)

Discovery of a heavy quarkonium-dominated state (~1.2 GeV) in vacuum

Temperature-induced interchange of meson roles during chiral restoration

Abstract

We investigate the implications of a tetraquark field on chiral symmetry restoration at nonzero temperature. In order for the chiral phase transition to be cross-over, as shown by lattice QCD studies, a strong mixing between scalar quarkonium and tetraquark fields is required. This leads to a light ($\sim0.4$ GeV), predominantly tetraquark state, and a heavy ($\sim1.2$ GeV), predominantly quarkonium state in the vacuum, in accordance with recently advocated interpretations of spectroscopy data. The mixing even increases with temperature and leads to an interchange of the roles of the originally heavy, predominantly quarkonium state and the originally light, predominantly tetraquark state. Then, as expected, the scalar quarkonium is a light state when becoming degenerate in mass with the pion as chiral symmetry is restored at nonzero temperature.