267 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
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
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
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
Lifetime Effects in Color Superconductivity at Weak Coupling
Present computations of the gap of color superconductivity in weak coupling
assume that the quarks which participate in the condensation process are
infinitely long-lived. However, the quasiparticles in a plasma are
characterized by having a finite lifetime. In this article we take into account
this fact to evaluate its effect in the computation of the color gap. By first
considering the Schwinger-Dyson equations in weak coupling, when one-loop
self-energy corrections are included, a general gap equation is written in
terms of the spectral densities of the quasiparticles. To evaluate lifetime
effects, we then model the spectral density by a Lorentzian function. We argue
that the decay of the quasiparticles limits their efficiency to condense. The
value of the gap at the Fermi surface is then reduced. To leading order, these
lifetime effects can be taken into account by replacing the coupling constant
of the gap equation by a reduced effective one.Comment: 16 pages, 2 figures; explanations on the role of the Meissner effect
added; 2 references added; accepted for publication in PR
Masses of the pseudo-Nambu-Goldstone bosons in two flavor color superconducting phase
The masses of the pseudo-Nambu-Goldstone bosons in the color superconducting
phase of dense QCD with two light flavors are estimated by making use of the
Cornwall-Jackiw-Tomboulis effective action. Parametrically, the masses of the
doublet and antidoublet bosons are suppressed by a power of the coupling
constant as compared to the value of the superconducting gap. This is
qualitatively different from the mass expression for the singlet
pseudo-Nambu-Goldstone boson, resulting from non-perturbative effects. It is
argued that the (anti-) doublet pseudo-Nambu-Goldstone bosons form colorless
[with respect to the unbroken SU(2)_{c}] charmonium-like bound states. The
corresponding binding energy is also estimated.Comment: 18 pages and 1 figure. REVTeX. New references and Appendix C with a
discussion of the gauge invariance in color superconductivity are added. To
appear in Phys. Rev.
Van der Waals Excluded Volume Model of Multicomponent Hadron Gas
A generalization of the Van der Waals excluded volume procedure for the
multicomponent hadron gas is proposed. The derivation is based on the grand
canonical partition function for the system of particles of several species
interacting by hard core potentials. The obtained formulae for thermodynamical
quantities are consistent with underlying principles of statistical mechanics
as well as with thermodynamical identities. The model can be applied to the
analysis of experimental data for particle number ratios in relativistic
nucleus-nucleus collisions.Comment: 8 page
Chiral Phase Transition within Effective Models with Constituent Quarks
We investigate the chiral phase transition at nonzero temperature and
baryon-chemical potential within the framework of the linear sigma
model and the Nambu-Jona-Lasinio model. For small bare quark masses we find in
both models a smooth crossover transition for nonzero and and a
first order transition for T=0 and nonzero . We calculate explicitly the
first order phase transition line and spinodal lines in the plane.
As expected they all end in a critical point. We find that, in the linear sigma
model, the sigma mass goes to zero at the critical point. This is in contrast
to the NJL model, where the sigma mass, as defined in the random phase
approximation, does not vanish. We also compute the adiabatic lines in the
plane. Within the models studied here, the critical point does not
serve as a ``focusing'' point in the adiabatic expansion.Comment: 22 pages, 18 figure
- âŠ