149 research outputs found
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
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
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
Population clustering as a signal for deconfinement in accreting compact stars
We study the evolution of the rotation frequency for accreting compact stars.
The discontinuous change of the moment of inertia of a rapidly rotating star
due to the possible quark core appearance entails a characteristic change in
the spin evolution. Numerical solutions have been performed using a model
equation of state describing the deconfinement phase transition. Trajectories
of spin evolution are discussed in the angular velocity - baryon number plane
(phase diagram) for different accretion scenarios defined by the initial values
of mass and magnetic field of the star, as well as mass accretion rate and
magnetic field decay time. We observe a characteristic increase in the waiting
time when a configuration enters the quark core regime. Overclustering of the
population of Z sources of LMXBs in the phase diagram is suggested as a direct
measurement of the critical line for the deconfinement phase transition since
it is related to the behaviour of the moment of inertia of the compact star.Comment: 6 pages, 4 figures, uses aastex.cls (included), text and figures
revised, references update
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
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