121 research outputs found
Probing the QCD phase diagram with fluctuations
The relevance of higher order cumulants of conserved charges for the analysis
of freeze-out and critical conditions in heavy ion collisions at LHC and RHIC
is discussed. Using properties of scaling functions, the generic
structure of these higher cumulants at vanishing baryon chemical potential is
discussed. Chiral model calculations are then used to study their properties at
non-zero baryon chemical potential. It is argued that the rapid variation of
sixth and higher order cumulants at the phase boundary may be used to explore
the QCD phase diagram in experiment. Moreover, results for the Polyakov loop
susceptibilities in SU(3) lattice gauge theory as well as in (2+1) flavor
lattice QCD are discussed. An analysis of the ratios of susceptibilities
indicates that the deconfinement transition is reflected in characteristic
modifications of these ratios.Comment: 14 pages, 6 figures. To appear in the G.E. Brown memorial volume in
NP
P-Wave Polarization of the -Meson and the Dilepton Spectrum in Dense Matter
We study the -wave polarization operator of the -meson due to interactions via the (1720) and resonances and compute
the corresponding production rate for -pairs at finite temperature and
baryon density. At high baryon density we find a significant shift of the
spectrum to lower invariant masses.Comment: 22 pages, 8 Postscript figures, uses article.sty, epsf.sty,
epsfig.st
Phase transitions at finite density
I discuss the analytic structure of thermodynamic quantities for complex
values of thermodynamic variables within Landau theory. In particular, the
singularities connected with phase transitions of second order, first order and
cross over types are examined. A conformal mapping is introduced, which may be
used to explore the thermodynamics of strongly interacting matter at finite
values of the baryon chemical potential starting from lattice QCD results
at . This method allows us to improve the convergence of a
Taylor expansion about and to enhance the sensitivity to physical
singularities in the complex plane. The technique is illustrated by an
application to a second-order transition in a chiral effective model.Comment: 10 pages, 8 figures, Presented at the HIC for FAIR Workshop and
XXVIII Max Born Symposium "Three days on Quarkyonic Island", Wroclaw, Poland,
19-21 May, 2011, reference corrected, two typos correcte
Weak and strong coupling limits of the Boltzmann equation in the relaxation-time approximation
We consider a momentum dependent relaxation time for the Boltzmann equation
in the relaxation time approximation. We employ a power law parametrization for
the momentum dependence of the relaxation time, and calculate the shear and
bulk viscosity, as well as, the charge and heat conductivity. We show, that for
the two popular parametrizations, referred to as the linear and quadratic
ansatz, one can obtain transport coefficients which corresponds to the weak and
strong coupling regimes, respectively. We also show that, for a system of
massless particles with vanishing chemical potential, the off-equilibrium
corrections to the phase-space distribution function calculated with the
quadratic ansatz are identical with those of the Grad's 14-moment method.Comment: 6 page
Relativistic second-order dissipative hydrodynamics at finite chemical potential
Starting from the Boltzmann equation in the relaxation time approximation and
employing a Chapman-Enskog like expansion for the distribution function close
to equilibrium, we derive second-order evolution equations for the shear stress
tensor and the dissipative charge current for a system of massless quarks and
gluons. The transport coefficients are obtained exactly using quantum
statistics for the phase space distribution functions at non-zero chemical
potential. We show that, within the relaxation time approximation, the
second-order evolution equations for the shear stress tensor and the
dissipative charge current can be decoupled. We find that, for large values of
the ratio of chemical potential to temperature, the charge conductivity is
small compared to the coefficient of shear viscosity. Moreover, we show that in
the relaxation-time approximation, the limiting behaviour of the ratio of heat
conductivity to shear viscosity is qualitatively similar to that obtained for a
strongly coupled conformal plasma.Comment: v3: 6 pages, 2 figure, published versio
Criticality of the net-baryon number probability distribution at finite density
We compute the probability distribution of the net-baryon number at
finite temperature and quark-chemical potential, , at a physical value of
the pion mass in the quark-meson model within the functional renormalization
group scheme. For , the model exhibits the chiral crossover transition
which belongs to the universality class of the spin system in three
dimensions. We explore the influence of the chiral crossover transition on the
properties of the net baryon number probability distribution, . By
considering ratios of to the Skellam function, with the same mean and
variance, we unravel the characteristic features of the distribution that are
related to criticality at the chiral crossover transition. We explore
the corresponding ratios for data obtained at RHIC by the STAR Collaboration
and discuss their implications. We also examine criticality in the
context of binomial and negative-binomial distributions for the net proton
number.Comment: 7 pages, 4 figures, to appear in Phys.Lett.
Polarization and dilepton anisotropy in pion-nucleon collisions
Hadronic polarization and the related anisotropy of the dilepton angular
distribution are studied for the reaction . We
employ consistent effective interactions for baryon resonances up to spin-5/2,
where non-physical degrees of freedom are eliminated, to compute the anisotropy
coefficients for isolated intermediate baryon resonances. It is shown that the
spin and parity of the intermediate baryon resonance is reflected in the
angular dependence of the anisotropy coefficient. We then compute the
anisotropy coefficient including the and resonances, which
are essential at the collision energy of the recent data obtained by the HADES
collaboration on this reaction. We conclude that the anisotropy coefficient
provides useful constraints for unravelling the resonance contributions to this
process.Comment: 11 pages, 5 figures, version accepted for publication in Physics
Letters
Modeling chiral criticality and its consequences for heavy-ion collisions
We explore the critical fluctuations near the chiral critical endpoint (CEP)
in a chiral effective model and discuss possible signals of the CEP, recently
explored experimentally in nuclear collision. Particular attention is paid to
the dependence of such signals on the location of the phase boundary and the
CEP relative to the chemical freeze-out conditions in nuclear collisions. We
argue that in effective models, standard freeze-out fits to heavy-ion data
should not be used directly. Instead, the relevant quantities should be
examined on lines in the phase diagram that are defined self-consistently,
within the framework of the model. We discuss possible choices for such an
approach.Comment: 4 pages, 4 figures, contribution to the Quark Matter 2015 proceeding
Polyakov loop fluctuations and deconfinement in the limit of heavy quarks
We explore the influence of heavy quarks on the deconfinement phase
transition in an effective model for gluons interacting with dynamical quarks
in color SU(3). With decreasing quark mass, the strength of the explicit
breaking of the Z(3) symmetry grows and the first-order transition ends in a
critical endpoint. The nature of the critical endpoint is examined by studying
the longitudinal and transverse fluctuations of the Polyakov loop, quantified
by the corresponding susceptibilities. The longitudinal susceptibility is
enhanced in the critical region, while the transverse susceptibility shows a
monotonic behavior across the transition point. We investigate the dependence
of the critical endpoint on the number of quark flavors at vanishing and finite
quark density. Finally we confront the model results with lattice calculations
and discuss a possible link between the hopping parameter and the quark mass.Comment: 8 pages, 9 figure
Probing deconfinement in the Polyakov-loop extended Nambu-Jona-Lasinio model at imaginary chemical potential
The phase structure of Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model
is explored at imaginary chemical potential, with particular emphasis on the
deconfinement transition. We point out that the statistical confinement nature
of the model naturally leads to characteristic dependence of the chiral
condensate on . We introduce a dual parameter for
the deconfinement transition by making use of this dependence. By changing a
four-fermion coupling constant, we tune the location of the critical endpoint
of the deconfinement transition.Comment: Talk presented at "Three Days on Quarkyonic Island", HIC for FAIR
workshop and XXVIII Max Born Symposium, Wroclaw, 19-21 May 2011. 10 pages, 6
figure
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