Phase diagram of two-color quark matter at nonzero baryon and isospin density

TL;DR

This paper maps the phase diagram of two-color, two-flavor quark matter at nonzero baryon and isospin densities, confirming the FF phase and analyzing the effects of the axial anomaly, with implications for lattice data and Bose-Einstein condensation.

Contribution

First model calculation of the full phase diagram at nonzero baryon and isospin density for two-color quark matter, including the FF phase and anomaly effects, bridging low and high density predictions.

Findings

Confirmed the presence of the Fulde-Ferrell phase.

Clarified the thermodynamic potential calculation with FF pairing.

Highlighted the importance of thermal fluctuations near Bose-Einstein condensation.

Abstract

We investigate the properties of cold dense quark matter composed of two colors and two flavors of light quarks. In particular, we perform the first model calculation of the full phase diagram at nonzero baryon and isospin density, thus matching the model-independent predictions of chiral perturbation theory at low density to the conjectured phase structure at high density. We confirm the presence of the Fulde-Ferrell (FF) phase in the phase diagram and study its dependence on the tunable parameter in the Lagrangian that simulates the effects of the quantum axial anomaly. As a byproduct, we clarify the calculation of the thermodynamic potential in the presence of the FF pairing, which was previously based on an ad hoc subtraction of an unphysical cutoff artifact. Furthermore, we argue that close to the diquark (or pion) Bose-Einstein condensation transition, the system behaves as a dilute Bose gas so that our simple fermionic model in the mean-field approximation is not quantitatively adequate. We suggest that including thermal fluctuations of the order parameter for Bose-Einstein condensation is crucial for understanding available lattice data.