635 research outputs found
Inhomogeneity driven by Higgs instability in gapless superconductor
The fluctuations of the Higgs and pseudo Nambu-Goldstone fields in the 2SC
phase with mismatched pairing are described in the nonlinear realization
framework of the gauged Nambu--Jona-Lasinio model. In the gapless 2SC phase,
not only Nambu-Goldstone currents can be spontaneously generated, but the Higgs
field also exhibits instablity. The Nambu-Goldstone currents generation
indicates the formation of the single plane wave LOFF state and breaks rotation
symmetry, while the Higgs instability favors spatial inhomogeneity and breaks
translation invariance. In this paper, we focus on the Higgs instability which
has not drawn much attention yet. The Higgs instability cannot be removed
without a long range force, thus it persists in the gapless superfluidity and
induces phase separation. In the case of g2SC state, the Higgs instability can
only be partially removed by the electric Coulomb energy. However, it is not
excluded that the Higgs instability might be completely removed in the charge
neutral gCFL phase by the color Coulomb energy.Comment: 21 pages, 5 figure
Spacetime Supersymmetry in a nontrivial NS-NS Superstring Background
In this paper we consider superstring propagation in a nontrivial NS-NS
background. We deform the world sheet stress tensor and supercurrent with an
infinitesimal B_{\mu\nu} field. We construct the gauge-covariant super-Poincare
generators in this background and show that the B_{\mu\nu} field spontaneously
breaks spacetime supersymmetry. We find that the gauge-covariant spacetime
momenta cease to commute with each other and with the spacetime supercharges.
We construct a set of "magnetic" super-Poincare generators that are conserved
for constant field strength H_{\mu\nu\lambda}, and show that these generators
obey a "magnetic" extension of the ordinary supersymmetry algebra.Comment: 13 pages, Latex. Published versio
Thermal Phase Transitions and Gapless Quark Spectra in Quark Matter at High Density
Thermal color superconducting phase transitions in three-flavor quark matter
at high baryon density are investigated in the Ginzburg-Landau (GL) approach.
We constructed the GL potential near the boundary with a normal phase by taking
into account nonzero quark masses, electric charge neutrality, and color charge
neutrality. We found that the density of states averaged over paired quarks
plays a crucial role in determining the phases near the boundary. By performing
a weak coupling calculation of the parameters characterizing the GL potential
terms of second order in the pairing gap, we show that three successive
second-order phase transitions take place as the temperature increases: a
modified color-flavor locked phase (ud, ds, and us pairings) -> a ``dSC'' phase
(ud and ds pairings) -> an isoscalar pairing phase (ud pairing) -> a normal
phase (no pairing). The Meissner masses of the gluons and the number of gapless
quark modes are also studied analytically in each of these phases.Comment: 15 pages, 6 figure
Higgs Mechanism in String Theory
In first-quantized string theory, spacetime symmetries are described by inner
automorphisms of the underlying conformal field theory. In this paper we use
this approach to illustrate the Higgs effect in string theory. We consider
string propagation on M^{24,1} \times S^1, where the circle has radius R, and
study SU(2) symmetry breaking as R moves away from its critical value. We find
a gauge-covariant equation of motion for the broken-symmetry gauge bosons and
the would-be Goldstone bosons. We show that the Goldstone bosons can be
eliminated by an appropriate gauge transformation. In this unitary gauge, the
Goldstone bosons become the longitudinal components of massive gauge bosons.Comment: 12 pages, Te
Influence of finite quark chemical potentials on the three flavor LOFF phase of QCD
We study in the Ginzburg-Landau approximation, the
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors and one
plane wave, including terms of order O(1/mu). We show that the LOFF window is
slightly enlarged, and actually splits into two different regions, one
characterized by u-s and d-u pairings and the other with d-u pairs only.Comment: 8 pages, 3 figure
Gauge Field Fluctuations and First-Order Phase Transition in Color Superconductivity
We study the gauge field fluctuations in dense quark matter and determine the
temperature of the induced first-order phase transition to the
color-superconducting phase in weak coupling. We find that the local
approximation of the coupling between the gauge potential and the order
parameter, employed in the Ginzburg-Landau theory, has to be modified by
restoring the full momentum dependence of the polarization function of gluons
in the superconducting phase.Comment: 5 pages, 1 figure, Revtex, we have modified our conclusions for the
metallic superconducto
Ginzburg-Landau approach to the three flavor LOFF phase of QCD
We explore, using a Ginzburg-Landau expansion of the free energy, the
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors, using
the NJL four-fermion coupling to mimic gluon interactions. We find that, below
the point where the QCD homogeneous superconductive phases should give way to
the normal phase, Cooper condensation of the pairs u-s and d-u is possible, but
in the form of the inhomogeneous LOFF pairing.Comment: 8 pages, 4 figures. Eq. (20) corrected. As a consequence figures have
been modified to show only the solution with parallel total momenta of the
us, ud pairs, as the other configurations are suppressed. Main conclusions of
the paper are unchange
Anisotropic Null String Cosmologies
We study string propagation in an anisotropic, cosmological background. We
solve the equations of motion and the constraints by performing a perturbative
expansion of the string coordinates in powers of c^2, the world-sheet speed of
light. To zeroth order the string is approximated by a tensionless string
(since c is proportional to the string tension T). We obtain exact, analytical
expressions for the zeroth and the first order solutions and we discuss some
cosmological implications.Comment: 9 pages, plain Te
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