QCD at finite isospin chemical potential

TL;DR

This paper explores the phase structure and equation of state of QCD at finite isospin chemical potential using lattice simulations, providing new insights into pion condensation and potential cosmological applications.

Contribution

It introduces a novel lattice simulation approach for QCD at finite isospin chemical potential, including phase diagram updates and initial equation of state results.

Findings

Identification of pion condensation phase at finite isospin chemical potential

First determination of QCD equation of state in this regime

Comparison with Taylor expansion methods

Abstract

We investigate the properties of QCD at finite isospin chemical potential at zero and non-zero temperatures. This theory is not affected by the sign problem and can be simulated using Monte-Carlo techniques. With increasing isospin chemical potential and temperatures below the deconfinement transition the system changes into a phase where charged pions condense, accompanied by an accumulation of low modes of the Dirac operator. The simulations are enabled by the introduction of a pionic source into the action, acting as an infrared regulator for the theory, and physical results are obtained by removing the regulator via an extrapolation. We present an update of our study concerning the associated phase diagram using 2+1 flavours of staggered fermions with physical quark masses and the comparison to Taylor expansion. We also present first results for our determination of the equation of state at finite isospin chemical potential and give an example for a cosmological application. The results can also be used to gain information about QCD at small baryon chemical potentials using reweighting with respect to the pionic source parameter and the chemical potential and we present first steps in this direction.