Bound States and Superconductivity in Dense Fermi Systems

TL;DR

This paper develops a quantum field theoretical framework to study the thermodynamics of dense Fermi systems, focusing on the formation, dissolution, and phase transitions of bound states and condensates in quark matter.

Contribution

It introduces a model to analyze chiral and superconducting phase transitions, including the BEC-BCS crossover and Mott effect, in dense quark matter using the NJL model.

Findings

Phase diagram shows coexistence of chiral symmetry breaking and color superconductivity.

Identifies the Mott transition as the dissolution of bound states into scattering states.

Highlights the role of the Pauli principle in the Mott transition of pions.

Abstract

A quantum field theoretical approach to the thermodynamics of dense Fermi systems is developed for the description of the formation and dissolution of quantum condensates and bound states in dependence of temperature and density. As a model system we study the chiral and superconducting phase transitions in two-flavor quark matter within the NJL model and their interrelation with the formation of quark-antiquark and diquark bound states. The phase diagram of quark matter is evaluated as a function of the diquark coupling strength and a coexistence region of chiral symmetry breaking and color superconductivity is obtained at very strong coupling. The crossover between Bose-Einstein condensation (BEC) of diquark bound states and condensation of diquark resonances (Cooper pairs) in the continuum (BCS) is discussed as a Mott effect. This effect consists in the transition of bound states into the continuum of scattering states under the influence of compression and heating. We explain the physics of the Mott transition with special emphasis on role of the Pauli principle for the case of the pion in quark matter.