Chiral dynamics in the low-temperature phase of QCD

TL;DR

This paper explores the low-temperature phase of QCD with two light quark flavors, analyzing chiral dynamics, excitations, and static observables near the crossover temperature using chiral expansion and MEM.

Contribution

It provides new insights into the chiral excitation spectrum and tests chiral perturbation theory predictions in the crossover region of QCD.

Findings

Identifies a sharp real-time excitation with pion quantum numbers.

Determines the dispersion relation of this excitation.

Finds mild dependence of static observables on quark mass near the crossover.

Abstract

We investigate the low-temperature phase of QCD and the crossover region with two light flavors of quarks. The chiral expansion around the point $(T, m_q = 0)$ in the temperature vs. quark-mass plane indicates that a sharp real-time excitation exists with the quantum numbers of the pion. We determine its dispersion relation and test the applicability of the chiral expansion. The time-dependent correlators are also analyzed using the Maximum Entropy Method (MEM), yielding consistent results. Finally, we test the predictions of ordinary chiral perturbation theory around the point $(T = 0, m_q = 0)$ for the temperature dependence of static observables. Around the crossover temperature, we find that all quantities considered depend only mildly on the quark mass in the considered range 8MeV $\leq \bar{m}^{\bar{\text{MS}}} \leq$ 15MeV.