609 research outputs found
Dimensional reduction and a Z(3) symmetric model
We present first results from a numerical investigation of a Z(3) symmetric
model based on dimensional reduction.Comment: Talk presented at XXI International Symposium on Lattice Field Theory
lattice2003(Non-zero temperature and density
Thermodynamics of the PNJL model with nonzero baryon and isospin chemical potentials
We have extended the Polyakov-Nambu-Jona-Lasinio (PNJL) model for two
degenerate flavours to include the isospin chemical potential (). All
the diagonal and mixed derivatives of pressure with respect to the quark number
(proportional to baryon number) chemical potential () and isospin
chemical potential upto sixth order have been extracted at .
These derivatives give the generalized susceptibilities with respect to quark
and isospin numbers. Similar estimates for the flavour diagonal and
off-diagonal susceptibilities are also presented. Comparison to Lattice QCD
(LQCD) data of some of these susceptibilities for which LQCD data are
available, show similar temperature dependence, though there are some
quantitative deviations above the crossover temperature. We have also looked at
the effects of instanton induced flavour-mixing coming from the chiral
symmetry breaking 't Hooft determinant like term in the NJL part of the model.
The diagonal quark number and isospin susceptibilities are completely
unaffected. The off-diagonal susceptibilities show significant dependence near
the crossover. Finally we present the chemical potential dependence of specific
heat and speed of sound within the limits of chemical potentials where neither
diquarks nor pions can condense.Comment: 15 pages, 7 figures, Added discussions and references, version to
appear in Phys. Rev.
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
Another weak first order deconfinement transition: three-dimensional SU(5) gauge theory
We examine the finite-temperature deconfinement phase transition of
(2+1)-dimensional SU(5) Yang-Mills theory via non-perturbative lattice
simulations. Unsurprisingly, we find that the transition is of first order,
however it appears to be weak. This fits naturally into the general picture of
"large" gauge groups having a first order deconfinement transition, even when
the center symmetry associated with the transition might suggest otherwise.Comment: 17 pages, 8 figure
Color superconductivity in weak coupling
We derive perturbatively the gap equations for a color-superconducting
condensate with total spin J=0 in dense QCD. At zero temperature, we confirm
the results of Son for the dependence of the condensate on the coupling
constant, and compute the prefactor to leading logarithmic accuracy. At nonzero
temperature, we find that to leading order in weak coupling, the temperature
dependence of the condensate is identical to that in BCS-like theories. The
condensates for total spin J=1 are classified; to leading logarithmic accuracy
these condensates are of the same order as those of spin J=0.Comment: 30 pages, 3 figures, RevTeX, epsf and psfig style files require
Small, Dense Quark Stars from Perturbative QCD
As a model for nonideal behavior in the equation of state of QCD at high
density, we consider cold quark matter in perturbation theory. To second order
in the strong coupling constant, , the results depend sensitively on
the choice of the renormalization mass scale. Certain choices of this scale
correspond to a strongly first order chiral transition, and generate quark
stars with maximum masses and radii approximately half that of ordinary neutron
stars. At the center of these stars, quarks are essentially massless.Comment: ReVTeX, 5 pages, 3 figure
Possibility of spontaneous parity violation in hot QCD
We suggest that for QCD in the limit of a large number of colors, N, the
axial U(1) symmetry of massless quarks is effectively restored at the
deconfining=chiral phase transition. If the deconfining transition is of second
order, then the chiral transition is weakly first order. In this case,
metastable states in which parity is spontaneously broken appear at
temperatures below the phase transition. The production of these metastable
states would have dramatic signatures, including enhanced production of eta and
eta' mesons, which can decay through parity violating decay processes such as
eta -> pi^0 pi^0, and global parity odd asymmetries for charged pions. Using a
nonlinear sigma model, in QCD these metastable states only appear rather near
the phase transition.Comment: 4 pages, REVTe
QCD and the Chiral Critical Point
As an extension of , consider a theory with ``'' flavors, where the
current quark masses are held in a fixed ratio as the overall scale of the
quark masses is varied. At nonzero temperature and baryon density it is
expected that in the chiral limit the chiral phase transition is of first
order. Increasing the quark mass from zero, the chiral transition becomes more
weakly first order, and can end in a chiral critical point. We show that the
only massless field at the chiral critical point is a sigma meson, with the
universality class that of the Ising model. Present day lattice simulations
indicate that is (relatively) near to the chiral critical point.Comment: 7 pages + 2 figures, BNL-GGP-
PNJL model with a Van der Monde term
We extend the Polyakov-Nambu-Jona-Lasinio (PNJL) model for two degenerate
flavours by including the effect of the SU(3) measure with a Van der Monde
(VdM) term. This ensures that the Polyakov loop always remains in the domain
[0,1]. The pressure, energy density, specific heat, speed of sound and
conformal measure show small or negligible effects from this term. However
various quark number and isospin susceptibilities are all found to approach
their respective ideal gas limits around 2 . We compare our methods with
other similar approaches in PNJL model and also present a quantitative
comparison with Lattice QCD data.Comment: 12 pages, 8 eps figures; extended discussion and reference added;
accepted in Phys. Rev.
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