[Paper Review] A gap in the quarkyonic matter

L. Ya. Glozman|ArXiv.org|Mar 11, 2008

Cold Atom Physics and Bose-Einstein Condensates3 citations

TL;DR

This paper demonstrates that quarkyonic matter—confined quarks and hadrons at high baryon density—exhibits a novel energy gap above the chiral restoration point, arising not from Cooper pairing but from the interplay of confinement and manifest chiral symmetry. This gap, absent below chiral restoration, fundamentally alters the system's low-energy dynamics and implies dissipationless processes, distinguishing it from conventional superfluids.

ABSTRACT

It has recently been suggested that at a reasonably large chemical potential a confining quarkyonic matter is formed that consists of the quark Fermi sea and confined hadrons on top of this Fermi sea. We study some properties of this matter. It is demonstrated that below the chiral restoration point there are gapless excitations of this matter through excitations of the Goldstone bosons. Above the chiral restoration point the single quarks are still removed from the spectrum of excitations and the only possible excitations are confined color-singlet hadrons with finite mass. Hence there appears a gap in the excitation spectrum of the quarkyonic matter that should be crucially important for its properties above the chiral restoration point. This gap is of a new type and is not related with the condensation of the fermionic system into a quasibosonic system. It is only due to such properties as confinement and manifest chiral symmetry at the same time.

Motivation & Objective

• To investigate the excitation spectrum of quarkyonic matter in the large-Nc limit of QCD.
• To determine whether gapless or gapped excitations emerge above the chiral restoration point.
• To clarify the origin of the gap in quarkyonic matter, distinguishing it from conventional BCS-type pairing.
• To establish that the gap arises solely from confinement and manifest chiral symmetry, not from fermionic condensation.
• To explore the implications of this gap for the low-energy dynamics and transport properties of quarkyonic matter.

Proposed method

• Use of a four-dimensional, exactly solvable confining and chirally symmetric model generalizing the 't Hooft model.
• Analysis of the quark Green function and Bethe-Salpeter equation in the presence of a Fermi sea at finite chemical potential.
• Study of meson spectra (pseudoscalar and scalar) as functions of Fermi momentum to identify chiral restoration and gap formation.
• Assessment of excitation spectra using a step-function momentum distribution near the Fermi surface, with extension to smoother distributions.
• Comparison of the system's behavior below and above the critical chemical potential where chiral symmetry is restored.
• Reliance on large-Nc arguments to argue for the generality of results beyond the specific model.

Experimental results

Research questions

• RQ1 Does quarkyonic matter exhibit a gap in its excitation spectrum above the chiral restoration point?
• RQ2 What is the physical origin of such a gap, and how does it differ from the BCS mechanism?
• RQ3 How do confinement and manifest chiral symmetry jointly lead to a gap without fermionic pairing?
• RQ4 What are the implications of this gap for dissipationless processes in quarkyonic matter?
• RQ5 To what extent do these results persist in real QCD with Nc = 3?

Key findings

• Above the chiral restoration point, quarkyonic matter exhibits a finite energy gap in its excitation spectrum, with no gapless Goldstone modes.
• The gap arises from the simultaneous presence of confinement and manifest chiral symmetry, not from Cooper pairing or quasibosonic condensation.
• The lowest excitation is a massive, confined, chirally symmetric hadron, whose energy sets the gap size.
• The gap increases with chemical potential and can become arbitrarily large in the large-Nc limit.
• The system supports dissipationless processes due to the gap, analogous to superfluidity but with a distinct microscopic origin.
• The results are robust and general, relying only on confinement and chiral symmetry restoration, not on the specific model details.