179 research outputs found
Gapless Color Superconductivity
We present the dispersion relations for quasiparticle excitations about the
color-flavor locked ground state of QCD at high baryon density. In the presence
of condensates which pair light and strange quarks there need not be an energy
gap in the quasiparticle spectrum. This raises the possibility of gapless color
superconductivity, with a Meissner effect but no minimum excitation energy.
Analysis within a toy model suggests that gapless color superconductivity may
occur only as a metastable phase.Comment: 4 pages, Revtex, eps figures include
Numerical solution of the color superconductivity gap in a weak coupling constant
We present the numerical solution of the full gap equation in a weak coupling
constant . It is found that the standard approximations to derive the gap
equation to the leading order of coupling constant are essential for a secure
numerical evaluation of the logarithmic singularity with a small coupling
constant. The approximate integral gap equation with a very small should be
inverted to a soft integral equation to smooth the logarithmic singularity near
the Fermi surface. The full gap equation is solved for a rather large coupling
constant . The approximate and soft integral gap equations are solved
for small values. When their solutions are extrapolated to larger
values, they coincide the full gap equation solution near the Fermi surface.
Furthermore, the analytical solution matches the numerical one up to the order
one O(1). Our results confirm the previous estimates that the gap energy is of
the order tens to 100 MeV for the chemical potential MeV. They
also support the validity of leading approximations applied to the full gap
equation to derive the soft integral gap equation and its analytical solution
near the Fermi surface.Comment: 7 pages+ 6 figs, Stanford, Frankfurt and Bethlehe
Which medical technology and/or local treatment is most conducive, as of 2012, to pressure sore debridement ? Developing French guidelines for clinical practice
AbstractIntroductionImplementation of a curative strategy at the debridement stage associates systemic therapy with local therapy.ObjectivesTo determine which medical devices and technology other than support surfaces and what kinds of drugs to use in order to cleanse a pressure ulcer in 2012.MethodA systematic review of the literature querying the databases PASCAL Biomed, Cochrane Library and PubMed from 2000 to 2010 along with a compendium of prevailing professional practices.ResultsPressure sore debridement is based on local care and on the use of alginates, hydrogels and hydrocolloids.DiscussionThe analyzed articles do not take into account any specific stage of pressure ulcer debridement. Data that might favor some kinds of dressings show a low level of evidence. Were it possible to decide on the dressing to be used for a given indication, professionals would be better able to orient and narrow down their choices.ConclusionUse of alginates and hydrogels in pressure ulcer debridement is of real interest. According to expert opinion, other dressings (irrigo-absorbents, for instance) seem promising, but have yet to receive adequate scientific validation
Quark description of nuclear matter
We discuss the role of an adjoint chiral condensate for color superconducting
quark matter. Its presence leads to color-flavor locking in two-flavor quark
matter. Color is broken completely as well as chiral symmetry in the two-flavor
theory with coexisting adjoint quark-antiquark and antitriplet quark-quark
condensates. The qualitative properties of this phase match the properties of
ordinary nuclear matter without strange baryons. This complements earlier
proposals by Schafer and Wilczek for a quark description of hadronic phases. We
show for a class of models with effective four-fermion interactions that
adjoint chiral and diquark condensates do not compete, in the sense that
simultaneous condensation occurs for sufficiently strong interactions in the
adjoint chiral channel.Comment: 15 pages, 3 figure
Charged and superconducting vortices in dense quark matter
Quark matter at astrophysical densities may contain stable vortices due to
the spontaneous breaking of hypercharge symmetry by kaon condensation. We argue
that these vortices could be both charged and electrically superconducting.
Current carrying loops (vortons) could be long lived and play a role in the
magnetic and transport properties of this matter. We provide a scenario for
vorton formation in protoneutron stars.Comment: Replaced with the published version. A typographical error in Eq. 2
is correcte
Spontaneous symmetry breaking in strong-coupling lattice QCD at high density
We determine the patterns of spontaneous symmetry breaking in strong-coupling
lattice QCD in a fixed background baryon density. We employ a
next-nearest-neighbor fermion formulation that possesses the SU(N_f)xSU(N_f)
chiral symmetry of the continuum theory. We find that the global symmetry of
the ground state varies with N_f and with the background baryon density. In all
cases the condensate breaks the discrete rotational symmetry of the lattice as
well as part of the chiral symmetry group.Comment: 10 pages, RevTeX 4; added discussion of accidental degeneracy of
vacuum after Eq. (35
Thermodynamics of two-colour QCD and the Nambu Jona-Lasinio model
We investigate two-flavour and two-colour QCD at finite temperature and
chemical potential in comparison with a corresponding Nambu and Jona-Lasinio
model. By minimizing the thermodynamic potential of the system, we confirm that
a second order phase transition occurs at a value of the chemical potential
equal to half the mass of the chiral Goldstone mode. For chemical potentials
beyond this value the scalar diquarks undergo Bose condensation and the diquark
condensate is nonzero. We evaluate the behaviour of the chiral condensate, the
diquark condensate, the baryon charge density and the masses of scalar diquark,
antidiquark and pion, as functions of the chemical potential. Very good
agreement is found with lattice QCD (N_c=2) results. We also compare with a
model based on leading-order chiral effective field theory.Comment: 24 pages, 12 figure
Angular Momentum Mixing in Crystalline Color Superconductivity
In crystalline color superconductivity, quark pairs form at non-zero total
momentum. This crystalline order potentially enlarges the domain of color
superconductivity in cold dense quark matter. We present a perturbative
calculation of the parameters governing the crystalline phase and show that
this is indeed the case. Nevertheless, the enhancement is modest, and to lowest
order is independent of the strength of the color interaction.Comment: 9 pages, 2 figures, Revte
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