Color superconductivity and the strange quark

At ultra-high density, matter is expected to form a degenerate Fermi gas of quarks in which there is a condensate of Cooper pairs of quarks near the Fermi surface: color superconductivity. In these proceedings I review some of the underlying physics, and discuss outstanding questions about the phase structure of ultra-dense quark matter.Comment: 11 pages, proceedings of QCD@Work 2005 and Johns Hopkins Workshop 200

Color Superconductivity in Dense, but not Asymptotically Dense, Quark Matter

At ultra-high density, matter is expected to form a degenerate Fermi gas of quarks in which there is a condensate of Cooper pairs of quarks near the Fermi surface: color superconductivity. In this chapter we review some of the underlying physics, and discuss outstanding questions about the phase structure of ultra-dense quark matter. We then focus on describing recent results on the crystalline color superconducting phase that may be the preferred form of cold, dense but not asymptotically dense, three-flavor quark matter. The gap parameter and free energy for this phase have recently been evaluated within a Ginzburg-Landau approximation for many candidate crystal structures. We describe the two that are most favorable. The robustness of these phases results in their being favored over wide ranges of density. However, it also implies that the Ginzburg-Landau approximation is not quantitatively reliable. We describe qualitative insights into what makes a crystal structure favorable which can be used to winnow the possibilities. We close with a look ahead at the calculations that remain to be done in order to make quantitative contact with observations of compact stars.Comment: 37 pages, 7 figures. To appear as a Chapter in "Pairing in Fermionic Systems: Basic Concepts and Modern Applications", published by World Scientifi

Color-Flavor Locking and Chiral Symmetry Breaking in High Density QCD

We propose a symmetry breaking scheme for QCD with three massless quarks at high baryon density wherein the color and flavor SU(3)_color times SU(3)_L times SU(3)_R symmetries are broken down to the diagonal subgroup SU(3)_{color+L+R} by the formation of a condensate of quark Cooper pairs. We discuss general properties that follow from this hypothesis, including the existence of gaps for quark and gluon excitations, the existence of Nambu-Goldstone bosons which are excitations of the diquark condensate, and the existence of a modified electromagnetic gauge interaction which is unbroken and which assigns integral charge to the elementary excitations. We present mean-field results for a Hamiltonian in which the interaction between quarks is modelled by that induced by single-gluon exchange. We find gaps of order 10-100 MeV for plausible values of the coupling. We discuss the effects of nonzero temperature, nonzero quark masses and instanton-induced interactions on our results.Comment: 17 pages, LaTeX. Factors of 2 corrected, figs and tables updated accordingl

What the Timing of Millisecond Pulsars Can Teach us about Their Interior

The cores of compact stars reach the highest densities in nature and therefore could consist of novel phases of matter. We demonstrate via a detailed analysis of pulsar evolution that precise pulsar timing data can constrain the star's composition, through unstable global oscillations (r-modes) whose damping is determined by microscopic properties of the interior. If not efficiently damped, these modes emit gravitational waves that quickly spin down a millisecond pulsar. As a first application of this general method, we find that ungapped interacting quark matter is consistent with both the observed radio and x-ray data, whereas for ordinary nuclear matter some additional enhanced damping mechanism is required.Comment: 6 pages, 5 figures, version to be published in PR