121 research outputs found
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
A Random Matrix Model for Color Superconductivity at Zero Chemical Potential
We discuss random matrix models for the spontaneous breaking of both chiral
and color symmetries at zero chemical potential and finite temperature.
Exploring different Lorentz and gauge symmetric color structures of the random
matrix interactions, we find that spontaneous chiral symmetry breaking is
always thermodynamically preferred over diquark condensation. Stable diquark
condensates appear only as SU(2) rotated chiral condensates, which do not
represent an independent thermodynamic phase. Our analysis is based on general
symmetry arguments and hence suggests that no stable and independent diquark
phase can form in QCD with two flavors at zero quark chemical potential.Comment: 26 pages, 1 figure, uses ReVTeX and epsf.st
Superfluid phase transition and strong-coupling effects in an ultracold Fermi gas with mass imbalance
We investigate the superfluid phase transition and effects of mass imbalance
in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation)
crossover regime of an cold Fermi gas. We point out that the Gaussian
fluctuation theory developed by Nozi\`eres and Schmitt-Rink and the -matrix
theory, that are now widely used to study strong-coupling physics of cold Fermi
gases, give unphysical results in the presence of mass imbalance. To overcome
this problem, we extend the -matrix theory to include higher-order pairing
fluctuations. Using this, we examine how the mass imbalance affects the
superfluid phase transition. Since the mass imbalance is an important key in
various Fermi superfluids, such as K-Li Fermi gas mixture, exciton
condensate, and color superconductivity in a dense quark matter, our results
would be useful for the study of these recently developing superfluid systems.Comment: 7 pages, 4 figures, Proceedings of QFS-201
Random matrix model for chiral symmetry breaking and color superconductivity in QCD at finite density
We consider a random matrix model which describes the competition between
chiral symmetry breaking and the formation of quark Cooper pairs in QCD at
finite density. We study the evolution of the phase structure in temperature
and chemical potential with variations of the strength of the interaction in
the quark-quark channel and demonstrate that the phase diagram can realize a
total of six different topologies. A vector interaction representing
single-gluon exchange reproduces a topology commonly encountered in previous
QCD models, in which a low-density chiral broken phase is separated from a
high-density diquark phase by a first-order line. The other five topologies
either do not possess a diquark phase or display a new phase and new critical
points. Since these five cases require large variations of the coupling
constants away from the values expected for a vector interaction, we conclude
that the phase diagram of finite density QCD has the topology suggested by
single-gluon exchange and that this topology is robust.Comment: ReVTeX, 22 pages, 14 figures. An animated gif movie showing the
evolution of the phase diagram with the coupling constants can be viewed at
http://www.nbi.dk/~vdheyden/QCDpd.htm
Superfluidity in a Model of Massless Fermions Coupled to Scalar Bosons
We study superfluidity in a model of massless fermions coupled to a massive
scalar field through a Yukawa interaction. Gap equations for a condensate with
total spin J=0 are solved in the mean-field approximation. For the Yukawa
interaction, the gaps for right- and left-handed fermions are equal in
magnitude and opposite in sign, so that condensation occurs in the J^P = 0^+
channel. At finite scalar mass, there are two different gaps for fermions of a
given chirality, corresponding to condensation of particle pairs or of
antiparticle pairs. These gaps become degenerate in the limit of infinite
scalar mass.Comment: 26 pages, 9 figures, RevTeX, epsf and psfig style files required.
Revised version, discussion of the excitation spectrum extended, Fig. 2 adde
Thermodynamics of the 3-flavor NJL model : chiral symmetry breaking and color superconductivity
Employing an extended three flavor version of the NJL model we discuss in
detail the phase diagram of quark matter. The presence of quark as well as of
diquark condensates gives raise to a rich structure of the phase diagram. We
study in detail the chiral phase transition and the color superconductivity as
well as color flavor locking as a function of the temperature and chemical
potentials of the system.Comment: 27 pages, 7 figure
Illuminating Dense Quark Matter
We imagine shining light on a lump of cold dense quark matter, in the CFL
phase and therefore a transparent insulator. We calculate the angles of
reflection and refraction, and the intensity of the reflected and refracted
light. Although the only potentially observable context for this phenomenon
(reflection of light from and refraction of light through an illuminated quark
star) is unlikely to be realized, our calculation casts new light on the old
idea that confinement makes the QCD vacuum behave as if filled with a
condensate of color-magnetic monopoles.Comment: 4 pages, 1 figur
On Color Superconductivity in External Magnetic Field
We study color superconductivity in external magnetic field. We discuss the
reason why the mixing angles in color-flavor locked (CFL) and two-flavor
superconductivity (2SC) phases are different despite the fact that the CFL gap
goes to the 2SC gap for . Although flavor symmetry is
explicitly broken in external magnetic field, we show that all values of gaps
in their coset spaces of possible solutions in the CFL phase are equivalent in
external magnetic field.Comment: 12 pages, LaTe
The Ginzburg-Landau Free Energy Functional of Color Superconductivity at Weak Coupling
We derive the Ginzburg-Landau free energy functional of color
superconductivity in terms of the thermal diagrams of QCD in its perturbative
region. The zero mode of the quadratic term coefficient yields the same
transition temperature, including the pre-exponential factor, as the one
obtained previously from the Fredholm determinant of the two quark scattering
amplitude. All coefficients of the free energy can be made identical to those
of a BCS model by setting the Fermi velocity of the latter equal to the speed
of light. We also calculate the induced symmetric color condensate near
and find that it scales as the cubic power of the dominant antisymmetric color
component. We show that in the presence of an inhomogeneity and a nonzero gauge
potential, while the color-flavor locked condensate dominates in the bulk, the
unlocked condensate, the octet, emerges as a result of a simultaneous
color-flavor rotation in the core region of a vortex filament or at the
junction of super and normal phases.Comment: 32 pages, Plain Tex, 3 figure
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
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