173 research outputs found
Out of Equilibrium Non-perturbative Quantum Field Dynamics in Homogeneous External Fields
The quantum dynamics of the symmetry broken lambda (Phi^2)^2 scalar field
theory in the presence of an homogeneous external field is investigated in the
large N limit. We choose as initial state the ground state for a constant
external field J .The sign of the external field is suddenly flipped from
J to - J at a given time and the subsequent quantum dynamics calculated.
Spinodal instabilities and parametric resonances produce large quantum
fluctuations in the field components transverse to the external field. This
allows the order parameter to turn around the maximum of the potential for
intermediate times. Subsequently, the order parameter starts to oscillate near
the global minimum for external field - J, entering a novel quasi-periodic
regime.Comment: LaTex, 30 pages, 12 .ps figures, improved version to appear in Phys
Rev
Ising-like dynamical signatures and the end-point of the QCD transition line
An increase in the size of coherent domains in the one component
field theory under the influence of a uniformly changing external magnetic
field near the critical end-point was proposed
recently as an estimate also for the variation of the chiral correlation length
of QCD near its respective hypothetical end point in the
plane. The present detailed numerical investigation of the effective model
suggests that passing by the critical QCD end point with realistic rate of
temperature change will trigger large amplitude oscillations in the temporal
variation of the chiral correlation length. A simple mechanism for producing
this phenomenon is suggested.Comment: 10 pages, RevTeX, 5 figures. Version accepted for publication in PR
The QCD equation of state at finite density from analytical continuation
We determine the equation of state of QCD at finite chemical potential, to
order , for a system of 2+1 quark flavors. The simulations are
performed at the physical mass for the light and strange quarks on several
lattice spacings; the results are continuum extrapolated using lattices of up
to temporal resolution. The QCD pressure and interaction measure are
calculated along the isentropic trajectories in the plane
corresponding to the RHIC Beam Energy Scan collision energies. Their behavior
is determined through analytic continuation from imaginary chemical potentials
of the baryonic density. We also determine the Taylor expansion coefficients
around from the simulations at imaginary chemical potentials.
Strangeness neutrality and charge conservation are imposed, to match the
experimental conditions.Comment: 5 pages, 4 figure
Fluctuations of conserved charges at finite temperature from lattice QCD
We present the full results of the Wuppertal-Budapest lattice QCD
collaboration on flavor diagonal and non-diagonal quark number susceptibilities
with 2+1 staggered quark flavors, in a temperature range between 125 and 400
MeV. The light and strange quark masses are set to their physical values.
Lattices with Nt=6, 8, 10, 12, 16 are used. We perform a continuum
extrapolation of all observables under study. A Symanzik improved gauge and a
stout-link improved staggered fermion action is utilized. All results are
compared to the Hadron Resonance Gas model predictions: good agreement is found
in the temperature region below the transition.Comment: 13 pages, 8 figures in Jhep styl
The running coupling of 8 flavors and 3 colors
We compute the renormalized running coupling of SU(3) gauge theory coupled to
N_f = 8 flavors of massless fundamental Dirac fermions. The recently proposed
finite volume gradient flow scheme is used. The calculations are performed at
several lattice spacings allowing for a controlled continuum extrapolation. The
results for the discrete beta-function show that it is monotonic without any
sign of a fixed point in the range of couplings we cover. As a cross check the
continuum results are compared with the well-known perturbative continuum
beta-function for small values of the renormalized coupling and perfect
agreement is found.Comment: 15 pages, 17 figures, published versio
Initial temperature and EoS of quark matter from direct photons
The time evolution of the quark gluon plasma created in gold-gold collisions
of the Relativistic Heavy Ion Collider (RHIC) can be described by
hydrodynamical models. Distribution of hadrons reflects the freeze-out state of
the matter. To investigate the time evolution one needs to analyze penetrating
probes, such as direct photon spectra. Distributions of low energy photons was
published in 2010 by PHENIX. In this paper we analyze a 3+1 dimensional
solution of relativistic hydrodynamics and calculate momentum distribution of
direct photons. Using earlier fits of this model to hadronic spectra, we
compare photon calculations to measurements and find that the initial
temperature of the center of the fireball is at least 519+-12 MeV, while for
the equation of state we get c_s= 0.36+-0.02.Comment: Talk at the VI Workshop on Particle Correlations and Femtoscopy,
Kiev, September 14-18, 2010. 6 pages, 1 figure. This work was supported by
the OTKA grant NK73143 and M. Csanad's Bolyai scholarshi
Equation of state in the PNJL model with the entanglement interaction
The equation of state and the phase diagram in two-flavor QCD are
investigated by the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model
with an entanglement vertex between the chiral condensate and the
Polyakov-loop. The entanglement-PNJL (EPNJL) model reproduces LQCD data at zero
and finite chemical potential better than the PNJL model. Hadronic degrees of
freedom are taken into account by the free-hadron-gas (FHG) model with the
volume-exclusion effect due to the hadron generation. The EPNJL+FHG model
improves agreement of the EPNJL model with LQCD data particularly at small
temperature. The quarkyonic phase survives, even if the correlation between the
chiral condensate and the Polyakov loop is strong and hadron degrees of freedom
are taken into account. However, the location of the quarkyonic phase is
sensitive to the strength of the volume exclusion.Comment: 9 pages, 7 figure
QCD equation of state at nonzero chemical potential: continuum results with physical quark masses at order mu^2
We determine the equation of state of QCD for nonzero chemical potentials via
a Taylor expansion of the pressure. The results are obtained for N_f=2+1
flavors of quarks with physical masses, on various lattice spacings. We present
results for the pressure, interaction measure, energy density, entropy density,
and the speed of sound for small chemical potentials. At low temperatures we
compare our results with the Hadron Resonance Gas model. We also express our
observables along trajectories of constant entropy over particle number. A
simple parameterization is given (the Matlab/Octave script parameterization.m,
submitted to the arXiv along with the paper), which can be used to reconstruct
the observables as functions of T and mu, or as functions of T and S/N.Comment: 14 pages, 15 figures, version accepted for publication in JHE
2PI effective action for gauge theories: Renormalization
We discuss the application of two-particle-irreducible (2PI) functional
techniques to gauge theories, focusing on the issue of non-perturbative
renormalization. In particular, we show how to renormalize the photon and
fermion propagators of QED obtained from a systematic loop expansion of the 2PI
effective action. At any finite order, this implies introducing new
counterterms as compared to the usual ones in perturbation theory. We show that
these new counterterms are consistent with the 2PI Ward identities and are
systematically of higher order than the approximation order, which guarantees
the convergence of the approximation scheme. Our analysis can be applied to any
theory with linearly realized gauge symmetry. This is for instance the case of
QCD quantized in the background field gauge.Comment: 21 pages, 8 figures. Uses JHEP3.cl
The QCD phase diagram at nonzero quark density
We determine the phase diagram of QCD on the \mu-T plane for small to
moderate chemical potentials. Two transition lines are defined with two
quantities, the chiral condensate and the strange quark number susceptibility.
The calculations are carried out on N_t =6,8 and 10 lattices generated with a
Symanzik improved gauge and stout-link improved 2+1 flavor staggered fermion
action using physical quark masses. After carrying out the continuum
extrapolation we find that both quantities result in a similar curvature of the
transition line. Furthermore, our results indicate that in leading order the
width of the transition region remains essentially the same as the chemical
potential is increased.Comment: 12 pages, 6 figure
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