Enhancement of quark number susceptibility with an alternative pattern of chiral symmetry breaking in dense matter

TL;DR

This paper investigates a novel phase in dense matter where chiral symmetry is broken via a quartic condensate while its center remains unbroken, revealing unique thermodynamic and hadronic properties.

Contribution

It introduces a new phase with quartic condensate-driven chiral symmetry breaking and analyzes its thermodynamic and hadronic implications using Ginzburg-Landau and linear sigma models.

Findings

Identification of a phase with unbroken center symmetry and broken chiral symmetry.

Discovery of a tricritical point between different symmetry phases.

Mass splitting of scalar and pseudoscalar mesons in the Z2 symmetric phase.

Abstract

We explore a possible phase where chiral $SU(2)_L \times SU(2)_R$ symmetry is spontaneously broken while its center $Z_2$ symmetry remains unbroken and its consequence on thermal quantities. In this phase, chiral symmetry breaking is driven by a quartic quark condensate although a bilinear quark condensate vanishes. A Ginzburg-Landau free energy leads to a new tricritical point (TCP) between the $Z_2$ broken and unbroken phases. Furthermore, a critical point can appear even in the chiral limit where explicit breaking is turned off, instead of a TCP at which restoration of chiral and its center symmetries takes place simultaneously. The net quark number density exhibits an abrupt change near the restoration of the center symmetry rather than that of the chiral symmetry. Hadron masses in possible phases are also studied in a linear sigma model. We show that, in the $Z_2$ symmetric phase, the $\bar{q}q$-type scalar meson with zero isospin I=0 splits from the $\bar{q}q$-type pseudoscalar meson with I=1.