Phase diagram of interacting pion matter and isospin charge fluctuations

TL;DR

This paper investigates the phase diagram and isospin charge fluctuations of interacting pion matter using a scalar field model, fitting lattice QCD data, and comparing scenarios with and without a first order phase transition.

Contribution

It introduces a self-interacting scalar field model for pion matter, fitted to lattice QCD results, and compares two phase transition scenarios to analyze charge fluctuations.

Findings

Qualitative differences in isospin charge susceptibilities between scenarios.

Both models fit lattice data well at zero temperature.

Differences in fluctuations can be tested by lattice simulations below 100 MeV.

Abstract

Equation of state and electric (isospin) charge fluctuations are studied for matter composed of interacting pions. The pion matter is described by self interacting scalar fields via a $\phi^4-\phi^6$ type Lagrangian. The mean-field approximation is used, and interaction parameters are fixed by fitting lattice QCD results on the isospin density as a function of the isospin chemical potential at zero temperature. Two scenarios for fixing the model parameters -- with and without the first order phase transition -- are considered, both yielding a satisfactory description of the lattice data. Thermodynamic functions and isospin charge fluctuations are studied and systematically compared for these two scenarios, yielding qualitative differences in the behavior of isospin charge susceptibilities. These differences can be probed by lattice simulations at temperatures $T \lesssim 100$ MeV.