Effective models of two-flavor QCD: from small towards large $m_q$

TL;DR

This paper compares effective chiral models coupled with the Polyakov loop to understand the phase structure of two-flavor QCD across different quark masses, highlighting similar behaviors and the difficulty in identifying the dominant symmetry near the physical point.

Contribution

It demonstrates that both linear sigma and Nambu-Jona-Lasinio models produce similar qualitative results when coupled with the Polyakov loop across varying quark masses, complicating symmetry identification.

Findings

Models show similar phase transition behaviors as quark mass increases.

Lattice data cannot conclusively determine the dominant symmetry near the physical point.

Both models suggest a complex interplay of symmetries in QCD phase transitions.

Abstract

We study effective models of chiral fields and Polyakov loop expected to describe the dynamics responsible for the phase structure of two-flavor QCD. We consider chiral sector described either using linear sigma model or Nambu-Jona-Lasinio model and study how these models, on the mean-field level when coupled with the Polyakov loop, behave as a function of increasing bare quark (or pion) mass. We find qualitatively similar behaviors for the cases of linear sigma model and Nambu-Jona-Lasinio model and, relating to existing lattice data, show that one cannot conclusively decide which or the two approximate symmetries drives the phase transitions near the physical point.