Surface effects in color superconducting strange-quark matter

TL;DR

This paper investigates the surface properties of color superconducting strange-quark matter using the Hartree-Fock-Bogoliubov approach within the MIT bag model, revealing charge distributions and energy characteristics relevant for strange star observations.

Contribution

It provides a detailed analysis of surface charge distributions and energy contributions in color superconducting strange-quark matter, incorporating pairing effects and boundary conditions.

Findings

Surface charge is positive near the surface due to quark density suppression.

In the CFL phase, total charge of strangelets is zero due to charge compensation.

Energy as a function of mass number fits a liquid-drop model with curvature term.

Abstract

Surface effects in strange-quark matter play an important role for certain observables which have been proposed in order to identify strange stars, and color superconductivity can strongly modify these effects. We study the surface of color superconducting strange-quark matter by solving the Hartree-Fock-Bogoliubov equations for finite systems ("strangelets") within the MIT bag model, supplemented with a pairing interaction. Due to the bag-model boundary condition, the strange-quark density is suppressed at the surface. This leads to a positive surface charge, concentrated in a layer of ~1 fm below the surface, even in the color-flavor locked (CFL) phase. However, since in the CFL phase all quarks are paired, this positive charge is compensated by a negative charge, which turns out to be situated in a layer of a few tens of fm below the surface, and the total charge of CFL strangelets is zero. We also study the surface and curvature contributions to the total energy. Due to the strong pairing, the energy as a function of the mass number is very well reproduced by a liquid-drop type formula with curvature term.