329 research outputs found
Gauge invariance of the color-superconducting gap on the mass shell
The gap parameter for color superconductivity is expected to be a gauge
invariant quantity, at least on the appropriate mass shell. Computing the gap
to subleading order in the QCD coupling constant, g, we show that the prefactor
of the exponential in 1/g is gauge dependent off the mass shell, and
independent of gauge on the mass shell.Comment: 8 pages, Proceedings of the Conference on Statistical QCD, Bielefeld,
August 26 - 30, 200
Color superconductivity in cold, dense quark matter
We review what is different and what is similar in a color superconductor as
compared to an ordinary BCS superconductor. The parametric dependence of the
zero-temperature gap on the coupling constant differs in QCD from that in BCS
theory. On the other hand, the transition temperature to the superconducting
phase is related to the zero-temperature gap in the same way in QCD as in BCS
theory.Comment: 11 pages, 1 figure, proceedings of the "Fifth Workshop on QCD",
Villefranche, Jan. 3-7, 200
Longitudinal gluons and Nambu-Goldstone bosons in a two-flavor color superconductor
In a two-flavor color superconductor, the SU(3)_c gauge symmetry is
spontaneously broken by diquark condensation. The Nambu-Goldstone excitations
of the diquark condensate mix with the gluons associated with the broken
generators of the original gauge group. It is shown how one can decouple these
modes with a particular choice of 't Hooft gauge. We then explicitly compute
the spectral density for transverse and longitudinal gluons of adjoint color 8.
The Nambu-Goldstone excitations give rise to a singularity in the real part of
the longitudinal gluon self-energy. This leads to a vanishing gluon spectral
density for energies and momenta located on the dispersion branch of the
Nambu-Goldstone excitations.Comment: 16 pages, 4 figures, minor revisions to text, one ref. adde
Effective gluon interactions in the Colour Superconductive Phase of two flavor QCD
The gluon self-energies and dispersion laws in the color superconducting
phase of QCD with two massless flavors are calculated using the effective
theory near the Fermi surface. These quantities are calculated at zero
temperature for all the eight gluons, those of the remaining SU(2) color group
and those corresponding to the broken generators. The construction of the
effective interaction is completed with the one loop calculation of the three-
and four-point gluon interactions.Comment: LaTeX, p 17, 4 figures. Final version to be published in Phys. Lett.
B. Several corrections have been done and some point clarifie
Differential freezeout and pion interferometry at RHIC from covariant transport theory
Puzzling discrepancies between recent pion interferometry data on Au+Au
reactions at s^1/2 = 130 and 200 AGeV from RHIC and predictions based on ideal
hydrodynamics are analyzed in terms of covariant parton transport theory. The
discrepancies of out and longitudinal radii are significantly reduced when the
finite opacity of the gluon plasma is taken into account.Comment: 4 pages, 3 EPS figures. Submitted to PR
Study of chiral symmetry restoration in linear and nonlinear O(N) models using the auxiliary field method
We consider the O(N) linear {\sigma} model and introduce an auxiliary field
to eliminate the scalar self-interaction. Using a suitable limiting process
this model can be continuously transformed into the nonlinear version of the
O(N) model. We demonstrate that, up to two-loop order in the CJT formalism, the
effective potential of the model with auxiliary field is identical to the one
of the standard O(N) linear {\sigma} model, if the auxiliary field is
eliminated using the stationary values for the corresponding one- and two-point
functions. We numerically compute the chiral condensate and the {\sigma}- and
{\pi}-meson masses at nonzero temperature in the one-loop approximation of the
CJT formalism. The order of the chiral phase transition depends sensitively on
the choice of the renormalization scheme. In the linear version of the model
and for explicitly broken chiral symmetry, it turns from crossover to first
order as the mass of the {\sigma} particle increases. In the nonlinear case,
the order of the phase transition turns out to be of first order. In the region
where the parameter space of the model allows for physical solutions,
Goldstone's theorem is always fulfilled.Comment: 25 pages, 9 figures, 1 table, improved versio
Azimuthal anisotropy: transition from hydrodynamic flow to jet suppression
Measured 2nd and 4th azimuthal anisotropy coefficients v_{2,4}(N_{part}),
p_T) are scaled with the initial eccentricity \varepsilon_{2,4}(N_{part}) of
the collision zone and studied as a function of the number of participants
N_{part} and the transverse momenta p_T. Scaling violations are observed for
p_T \alt 3 GeV/c, consistent with a dependence of viscous corrections
and a linear increase of the relaxation time with . These empirical
viscous corrections to flow and the thermal distribution function at freeze-out
constrain estimates of the specific viscosity and the freeze-out temperature
for two different models for the initial collision geometry. The apparent
viscous corrections exhibit a sharp maximum for p_T \agt 3 GeV/c, suggesting
a breakdown of the hydrodynamic ansatz and the onset of a change from
flow-driven to suppression-driven anisotropy.Comment: 5 pages, 4 figs; submitted for publicatio
Asymptotic deconfinement in high-density QCD
We discuss QCD with two light flavors at large baryon chemical potential mu.
Color superconductivity leads to partial breaking of the color SU(3) group. We
show that the infrared physics is governed by the gluodynamics of the remaining
SU(2) group with an exponentially soft confinement scale Lambda_QCD'
Delta*exp[-a*mu/(g*Delta)], where Delta<<mu is the superconducting gap, g is
the strong coupling, and a=0.81... We estimate that at moderate baryon
densities Lambda_QCD' is O(10 MeV) or smaller. The confinement radius increases
exponentially with density, leading to "asymptotic deconfinement." The velocity
of the SU(2) gluons is small due to the large dielectric constant of the
medium.Comment: 4 pages; restructured, published versio
Fluctuation modes in color-superconductors
We investigate fluctuation effects of a gap parameter in
color-superconductors. The fluctuation modes in the super phase are described
by two scalar fields of diquarks. One of them is a Nambu-Goldstone boson and
the other is a diquark boson whose mass is about twice of the gap energy (an
extended quasi-supersymmetry). In the normal phase the fluctuation becomes a
precursory (soft) mode whose amplitude increases near the critical temperature.Comment: 6 page
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