195 research outputs found
Coherent neutrino radiation in supernovae at two loops
We develop a neutrino transport theory, in terms of the real-time
non-equilibrium Green's functions, which is applicable to physical conditions
arbitrary far from thermal equilibrium. We compute the coherent neutrino
radiation in cores of supernovae by evaluating the two-particle-two-hole
(2p-2h) polarization function with dressed propagators. The propagator dressing
is carried out in the particle-particle channel to all orders in the
interaction. We show that at two loops there are two distinct sources of
coherence effects in the bremsstrahlung. One is the generically off-shell
intermediate state propagation, which leads to the Landau-Pomeranchuk-Migdal
type suppression of radiation. We extend previous perturbative results,
obtained in the leading order in quasiparticle width, by deriving the exact
non-perturbative expression. A new contribution due to off-shell finial/initial
baryon states is treated in the leading order in the quasiparticle width. The
latter contribution corresponds to processes of higher order than second order
in the virial expansion in the number of quasiparticles. At 2p-2h level, the
time component of the polarization tensor for the vector transitions vanishes
identically in the soft neutrino limit. Vector current thereby is conserved.
The contraction of the neutral axial vector current with tensor interaction
among the baryons leads to a non-vanishing contribution to the bremsstrahlung
rate. These rates are evaluated numerically for finite temperature pure neutron
matter at and above the nuclear saturation density.Comment: 26 pages, 5 figures, uses Revte
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
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