270 research outputs found
Accessibility of color superconducting quark matter phases in heavy-ion collisions
We discuss a hybrid equation of state (EoS) that fulfills constraints for
mass-radius relationships and cooling of compact stars. The quark matter EoS is
obtained from a Polyakov-loop Nambu--Jona-Lasinio (PNJL) model with color
superconductivity, and the hadronic one from a relativistic mean-field (RMF)
model with density-dependent couplings (DD-RMF). For the construction of the
phase transition regions we employ here for simplicity a Maxwell construction.
We present the phase diagram for symmetric matter which exhibits two remarkable
features: (1) a "nose"-like structure of the hadronic-to-quark matter phase
border with an increase of the critical density at temperatures below T ~ 150
MeV and (2) a high critical temperature for the border of the two-flavor color
superconducting (2SC) phase, T_c > 160 MeV. We show the trajectories of
heavy-ion collisions in the plane of excitation energy vs. baryon density
calculated using the UrQMD code and conjecture that for incident energies of 4
... 8 A GeV as provided, e.g., by the Nuclotron-M at JINR Dubna or by lowest
energies at the future heavy-ion collision experiments CBM@FAIR and NICA@JINR,
the color superconducting quark matter phase becomes accessible.Comment: 5 pages, 1 figure, Poster presented at the XXVI. Max Born Symposium
"Three Days of Strong Interactions", Wroclaw (Poland), July 9-11, 200
Strange and charm quark-pair production in strong non-Abelian field
We have investigated strange and charm quark-pair production in the early
stage of heavy ion collisions. Our kinetic model is based on a Wigner function
method for fermion-pair production in strong non-Abelian fields. To describe
the overlap of two colliding heavy ions we have applied the time-dependent
color field with a pulse-like shape. The calculations have been performed in an
SU(2)-color model with finite current quark masses. For strange quark-pair
production the obtained results are close to the Schwinger limit, as we
expected. For charm quark the large inverse temporal width of the field pulse,
instead of the large charm quark mass, determines the efficiency of the
quark-pair production. Thus we do not observe the expected suppression of charm
quark-pair production connecting to the usual Schwinger-formalism, but our
calculation results in a relatively large charm quark yield. This effect
appears in Abelian models as well, demonstrating that particle-pair production
for fast varying non-Abelian gluon field strongly deviates from the Schwinger
limit for charm quark. We display our results on number densities for light,
strange, charm quark-pairs, and different suppression factors as the function
of characteristic time of acting chromo-electric field.Comment: 6 pages, 2 figures; to appear in the proceedings of the International
Conference on Strangeness in Quark matter (SQM2008), Beijing, China, Oct
6-10, 2008; version accepted to J. Phys.
Coupled fermion and boson production in a strong background mean-field
We derive quantum kinetic equations for fermion and boson production starting
from a phi^4 Lagrangian with minimal coupling to fermions. Decomposing the
scalar field into a mean-field part and fluctuations we obtain spontaneous pair
creation driven by a self-interacting strong background field. The produced
fermion and boson pairs are self-consistently coupled. Consequently back
reactions arise from fermion and boson currents determining the time dependent
self-interacting background mean-field. We explore the numerical solution in
flux tube geometry for the time evolution of the mean-field as well as for the
number- and energy densities for fermions and bosons. We find that after a
characteristic time all energy is converted from the background mean-field to
particle creation. Applying this general approach to the production of
``quarks'' and ``gluons'' a typical time scale for the collapse of the flux
tube is 1.5 fm/c.Comment: 9 pages, latex, epsfig, 7 figure
Two-flavor QCD at finite temperature and chemical potential in a functional approach
We summarize recent results obtained in the Dyson-Schwinger formalism to
study the chiral and deconfinement phase transitions of quenched and unquenched
QCD at finite temperature and chemical potential. In the quenched case we
compare SU(2) and SU(3) gauge theories by taking lattice data for the gluon as
an input for the quark Dyson-Schwinger equation. As compared to previous
investigations we find a clearer distinction between the second order
transition of the two-color theory and the (weak) first order transition of the
three-color gauge theory. We then extend this study to unquenched QCD at finite
chemical potential by taking matter effects to the gluon into account and
investigate the order of the chiral phase transition and the behavior of the
deconfinement transition. What we find are coinciding phase transitions up to a
critical endpoint which is located at large chemical potential.Comment: 7 pages, 5 figures, contribution to the proceedings of the
International School of Nuclear Physics, Erice 201
Phase diagram in an external magnetic field beyond a mean-field approximation
The phase structure of the Polyakov loop-extended chiral quark-meson model is
explored in a nonperturbative approach, beyond a mean-field approximation, in
the presence of a magnetic field. We show that by including meson fluctuations
one cannot resolve the qualitative discrepancy on the dependence of the
crossover transition temperature in a non-zero magnetic field between effective
model predictions and recent lattice results (arXiv:1111.4956).We compute the
curvature of the crossover line in the T - {\mu}_B plane at a non-zero magnetic
field and show that the curvature increases with increasing magnetic field. On
the basis of QCD inequalities, we also argue that, at least in the large Nc
limit, a chiral critical end point and, consequently, a change from crossover
to a first-order chiral phase transition are excluded at zero baryon chemical
potential and non-zero magnetic field.Comment: 8 pages, 5 figure
Critical endpoint for deconfinement in matrix and other effective models
We consider the position of the deconfining critical endpoint, where the
first order transition for deconfinement is washed out by the presence of
massive, dynamical quarks. We use an effective matrix model, employed
previously to analyze the transition in the pure glue theory. If the param-
eters of the pure glue theory are unaffected by the presence of dynamical
quarks, and if the quarks only contribute perturbatively, then for three colors
and three degenerate quark flavors this quark mass is very heavy, m_de \sim 2.5
GeV, while the critical temperature, T_de, barely changes, \sim 1% below that
in the pure glue theory. The location of the deconfining critical endpoint is a
sensitive test to differentiate between effective models. For example, models
with a logarithmic potential for the Polyakov loop give much smaller values of
the quark mass, m_de \sim 1 GeV, and a large shift in T_de \sim 10% lower than
that in the pure glue theory.Comment: 16 pages; 3 figure
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