224 research outputs found
Isospin Chemical Potential and the QCD Phase Diagram at Nonzero Temperature and Baryon Chemical Potential
We use the Nambu--Jona-Lasinio model to study the effects of the isospin
chemical potential on the QCD phase diagram at nonzero temperature and baryon
chemical potential. We find that the phase diagram is qualitatively altered by
a small isospin chemical potential. There are two first order phase transitions
that end in two critical endpoints, and there are two crossovers at low baryon
chemical potential. These results have important consequences for systems where
both baryon and isospin chemical potentials are nonzero, such as heavy ion
collision experiments. Our results are in complete agreement with those
recently obtained in a Random Matrix Model.Comment: 4 pages, 1 figure, REVTeX
Lowest tensor-meson resonances contributions to the chiral perturbation theory low energy coupling constants
The contributions of the lightest tensor-meson resonances to the low-energy coupling constants of second order chiral perturbation theory with two flavours are evaluated and compared with the available phenomenological information as well as with similar results for other resonances
The QCD Phase Diagram at Non-zero Baryon and Isospin Chemical Potentials
In heavy ion collision experiments as well as in neutron stars, both baryon
and isospin chemical potentials are different from zero. In particular, the
regime of small isospin chemical potential is phenomenologically important.
Using a random matrix model, we find that the phase diagram at non-zero
temperature and baryon chemical potential is greatly altered by an arbitrarily
small isospin chemical potential: There are two first order phase transitions
at low temperature, two critical endpoints, and two crossovers at high
temperature. As a consequence, in the region of the phase diagram explored by
RHIC experiments, there are two crossovers that separate the hadronic phase
from the quark-gluon plasma phase at high temperature.Comment: 3 pages, 2 figures. Talk presented at Lattice2004(non-zero),
Fermilab, June 21 - 26, 200
Finite Density Lattice Gauge Theories with Positive Fermion Determinants
We perform simulations of (3-colour) QCD with 2 quark flavours at a finite
chemical potential for isospin(), and of 2-colour QCD at a finite
chemical potential for quark number. At zero temperature, QCD at finite
has a mean-field phase transition at to a superfluid
state with a charged pion condensate which spontaneously breaks . We study
the finite temperature transition as a function of . For , where this is closely related to the transition at finite , this
appears to be a crossover independent of quark mass, with no sign of the
proposed critical endpoint. For this becomes a true phase
transition where the pion condensate evaporates. For just above
the transition seems to be second order, while for larger it appears to
become first order. At zero temperature, 2-colour QCD also possesses a
superfluid state with a diquark condensate. We study its spectrum of Goldstone
and pseudo-Goldstone bosons associated with chiral and quark-number symmetry
breaking.Comment: 12 pages Latex/ptptex, 10 figures. Talk at Finite Density QCD, 2003,
Nara Revised to add 2 reference
Effective Low Energy Theories and QCD Dirac Spectra
We analyze the smallest Dirac eigenvalues by formulating an effective theory
for the QCD Dirac spectrum. We find that in a domain where the kinetic term of
the effective theory can be ignored, the Dirac eigenvalues are distributed
according to a Random Matrix Theory with the global symmetries of the QCD
partition function. The kinetic term provides information on the slope of the
average spectral density of the Dirac operator. In the second half of this
lecture we interpret quenched QCD Dirac spectra at nonzero chemical potential
(with eigenvalues scattered in the complex plane) in terms of an effective low
energy theory.Comment: Invited talk at the 10th International Conference on Recent Progress
in Many-Body Theories (MBX), Seattle, September 1999, 13 pages, Latex, with 1
figure, uses ws-p9-75x6-50.cl
Quark-Antiquark Condensates in the Hadronic Phase
We use a hadron resonance gas model to calculate the quark-antiquark
condensates for light (up and down) and strange quark flavors at finite
temperatures and chemical potentials. At zero chemical potentials, we find that
at the temperature where the light quark-antiquark condensates entirely vanish
the strange quark-antiquark condensate still keeps a relatively large fraction
of its value in the vacuum. This is in agreement with results obtained in
lattice simulations and in chiral perturbation theory at finite temperature and
zero chemical potentials. Furthermore, we find that this effect slowly
disappears at larger baryon chemical potential. These results might have
significant consequences for our understanding of QCD at finite temperatures
and chemical potentials. Concretely, our results imply that there might be a
domain of temperatures where chiral symmetry is restored for light quarks, but
still broken for strange quark that persists at small chemical potentials. This
might have practical consequences for heavy ion collision experiments.Comment: 5 pages, 7 figure
Diquark Condensation at Nonzero Chemical Potential and Temperature
SU(2) lattice gauge theory with four flavors of quarks is studied at nonzero
chemical potential and temperature by computer simulation and
Effective Lagrangian techniques. Simulations are done on ,
and lattices and the diquark condensate, chiral order
parameter, Wilson line, fermion energy and number densities are measured.
Simulations at a fixed, nonzero quark mass provide evidence for a tricritical
point in the - plane associated with diquark condensation. For low ,
increasing takes the system through a line of second order phase
transitions to a diquark condensed phase. Increasing at high , the
system passes through a line of first order transitions from the diquark phase
to the quark-gluon plasma phase. Using Effective Lagrangians we estimate the
position of the tricritical point and ascribe its existence to trilinear
couplings that increase with and .Comment: 18 pages revtex, 11 figures postscrip
QCD determination of the axial-vector coupling of the nucleon at finite temperature
A thermal QCD Finite Energy Sum Rule (FESR) is used to obtain the temperature
dependence of the axial-vector coupling of the nucleon, . We find
that is essentially independent of , in the very wide range , where is the critical temperature. While
at T=0 is -independent, it develops a dependence at
finite temperature. We then obtain the mean square radius associated with
and find that it diverges at , thus signalling quark
deconfinement. As a byproduct, we study the temperature dependence of the
Goldberger-Treiman relation.Comment: 8 pages and 3 figure
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