Angle-dependent Gap state in Asymmetric Nuclear Matter

TL;DR

This paper introduces an axisymmetric angle-dependent pairing state in isospin-asymmetric nuclear matter, which lowers free energy and enhances pairing near the Fermi surface, especially at high asymmetries.

Contribution

It proposes a novel angle-dependent gap state with broken rotational symmetry, showing its energetic favorability and transition properties in asymmetric nuclear matter.

Findings

The ADG state has lower free energy than the angle-averaged gap state at high isospin asymmetry.

The ADG state exhibits a larger pairing gap near the Fermi surface.

The transition from the ADG state to the normal state is second order and occurs at a critical asymmetry.

Abstract

We propose an axisymmetric angle-dependent gap (ADG) state with the broken rotational symmetry in isospin-asymmetric nuclear matter. In this state, the deformed Fermi spheres of neutrons and protons increase the pairing probabilities along the axis of symmetry breaking near the average Fermi surface. We find that the state possesses lower free energy and larger gap value than the angle-averaged gap state at large isospin asymmetries. These properties are mainly caused by the coupling of different m_{j} components of the pairing gap. Furthermore, we find the transition from the ADG state to the normal state is of second order and the ADG state vanishes at the critical isospin asymmetry m_{j} where the angle-averaged gap vanishes.