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.
Highlights
There is interest in the properties of quantum chromodynamics (QCD) at supranuclear densities ever since the first discussion of the possible existence of colorsuperconducting ground states in the 1970s, see Ref. [1] for an early review
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 nonperturbative low-energy regime which is found to be governed by the dynamical formation of diquark states
In this density regime, which is still relevant for astrophysical applications, QCD is widely expected to be governed by a color-superconducting ground state
Summary
There is interest in the properties of quantum chromodynamics (QCD) at supranuclear densities ever since the first discussion of the possible existence of colorsuperconducting ground states in the 1970s, see Ref. [1] for an early review. In the broad intermediate density regime, where both the chiral and the pQCD expansion are expected to break down, much less is known about the dynamical degrees of freedom and their interactions, resulting in large uncertainties for the EOS and other quantities, such as the speed of sound of dense matter. In this density regime, which is still relevant for astrophysical applications, QCD is widely expected to be governed by a color-superconducting ground state
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