Color-magnetic flux tubes in quark matter cores of neutron stars

We argue that if color-superconducting quark matter exists in the core of a neutron star, it may contain a high density of flux tubes, carrying flux that is mostly color-magnetic, with a small admixture of ordinary magnetic flux. We focus on the two-flavor color-superconducting ("2SC") phase, and assume that the flux tubes are energetically stable, although this has not yet been demonstrated. The density of flux tubes depends on the nature of the transition to the color-superconducting phase, and could be within an order of magnitude of the density of magnetic flux tubes that would be found if the core were superconducting nuclear matter. We calculate the cross-section for Aharonov-Bohm scattering of gapless fermions off the flux tubes, and the associated collision time and frictional force on a moving flux tube. We discuss the other forces on the flux tube, and find that if we take in to account only the forces that arise within the 2SC core region then the timescale for expulsion of the color flux tubes from the 2SC core is of order 10^10 years.Comment: 28 pages, LaTeX, 1 figure, 2 appendices; added discussion of energetic stability of flux tube

A Novel Mechanism for Type-I Superconductivity in Neutron Stars

We suggest a mechanism that may resolve a conflict raised by Link between the precession of a neutron star and the standard picture in which its core is composed of a mixture of a neutron superfluid and a type-II proton superconductor. We will show that if there is a persistent, non-dissipating current running along the magnetic flux tubes, the force between magnetic flux tubes may be attractive, resulting in a type-I, rather than a type-II, superconductor. If this is the case, the conflict between the observed precession and the canonical estimation of the Landau-Ginzburg parameter (which suggests type II behaviour) will be automatically resolved. Such a current arises in some condensed matter systems and may also appear in QCD dense matter as a consequence of quantum anomalies. We calculate the interaction between two vortices carrying a current j and find a constraint on the magnitude of j where a superconductor is always type-I, even when the cannonical Landau-Ginzburg parameter indicates type-II behaviour. If this condition is met, the magnetic field is expelled from the superconducting regions of the neutron star leading to the formation of the intermediate state where alternating domains of superconducting matter and normal matter coexist. We further argue that even when the induced current is small the vortex Abrikosov lattice will nevertheless be destroyed due to the helical instability studied previously in many condensed matter systems. This would also resolve the apparent contradiction with the precession of the neutron stars. We also discuss some instances where anomalous induced current may play a crucial role, such as the neutron star kicks, pulsar glitches and the toroidal magnetic field.Comment: 10 pages, Additional arguments are given supporting the idea that the Abrikosov lattice will be destroyed in regions where longitudinal currents are induce

Fluctuations of the Color-superconducting Order Parameter in Heated and Dense Quark Matter

Fluctuations of the color superconducting order parameter in dense quark matter at finite temperatures are investigated in terms of the phenomenological Ginzburg - Landau approach. Our estimates show that fluctuations of the di-quark gap may strongly affect some of thermodynamic quantities even far below and above the critical temperature. If the critical temperature of the di-quark phase transition were rather high one could expect a manifestation of fluctuations of the di-quark gap in the course of heavy ion collisions.Comment: 12

Tkachenko modes as sources of quasiperiodic pulsar spin variations

We study the long wavelength shear modes (Tkachenko waves) of triangular lattices of singly quantized vortices in neutron star interiors taking into account the mutual friction between the superfluid and the normal fluid and the shear viscosity of the normal fluid. The set of Tkachenko modes that propagate in the plane orthogonal to the spin vector are weakly damped if the coupling between the superfluid and normal fluid is small. In strong coupling, their oscillation frequencies are lower and are undamped for small and moderate shear viscosities. The periods of these modes are consistent with the observed ~100-1000 day variations in spin of PSR 1828-11.Comment: 7 pages, 3 figures, uses RevTex, v2: added discussion/references, matches published versio