From quarks and gluons to color superconductivity at supranuclear densities

TL;DR

This paper investigates color superconductivity in dense QCD matter using renormalization group flow, revealing the behavior of diquark condensates and the speed of sound at supranuclear densities, with implications for modeling dense matter.

Contribution

It introduces a RG-based approach to study color superconductivity, connecting high-energy quark-gluon dynamics to low-energy diquark formation and coupling behaviors.

Findings

Diquark condensate scales with chemical potential.

Couplings in low-energy models depend on density.

Speed of sound exceeds noninteracting quark gas at high densities.

Abstract

We study the emergence of color superconductivity in the theory of the strong interaction at supranuclear densities. To this end, we follow the renormalization group (RG) flow of dense strong-interaction matter with two massless quark flavors from the fundamental quark and gluon degrees of freedom at high energies down to the non-perturbative low-energy regime which is found to be governed by the dynamical formation of diquark states. With the strong coupling at the initial RG scale as the only input parameter, we compute the (chirally symmetric) scalar diquark condensate and analyze its scaling behavior over a wide range of the quark chemical potential. Approximations entering our computations are critically assessed. Since our approach naturally allows us to study the scale dependence of couplings, we also monitor the strength of couplings appearing in low-energy models of dense strong-interaction matter. The observed dependence of these couplings on the quark chemical potential may help to amend model studies in the future. Finally, we estimate the speed of sound of dense QCD matter. Our results indicate that the speed of sound exceeds the value of the noninteracting quark gas at high densities and even increases as the density is decreased, across a wide range, suggesting the existence of a maximum at supranuclear densities.