Role of two-flavor color superconductor pairing in a three-flavor Nambu--Jona-Lasinio model with axial anomaly

TL;DR

This paper investigates the phase diagram of strongly interacting matter using a three-flavor Nambu--Jona-Lasinio model, highlighting the importance of two-flavor color superconductivity and axial anomaly effects on phase structure.

Contribution

It demonstrates the necessity of including the 2SC phase and axial anomaly effects, revealing complex phase structures and the suppression of the low-temperature critical endpoint.

Findings

2SC phase can be favored even with equal quark masses due to axial anomaly

Rich phase structure including BCS- and BEC-like phases and new endpoints

Low-temperature critical endpoint is nearly removed from the phase diagram

Abstract

The phase diagram of strongly interacting matter is studied within a three-flavor Nambu--Jona-Lasinio model, which contains the coupling between chiral and diquark condensates through the axial anomaly. Our results show that it is essential to include the 2SC phase in the analysis. While this is expected for realistic strange quark masses, we find that even for equal up, down, and strange bare quark masses, 2SC pairing can be favored due to spontaneous flavor-symmetry breaking by the axial anomaly. This can lead to a rich phase structure, including BCS- and BEC-like 2SC and CFL phases and new endpoints. On the other hand, the low-temperature critical endpoint, which was found earlier in the same model without 2SC pairing, is almost removed from the phase diagram and cannot be reached from the low-density chirally broken phase without crossing a preceding first-order phase boundary. For physical quark masses no additional critical endpoint is found.