59 research outputs found
Fluctuations at finite temperature and density
Fluctuations of conserved charges in a grand canonical ensemble can be
calculated as derivatives of the free energy with respect to the respective
chemical potential. They are directly related to experimentally available
observables that describe the hadronization in heavy ion collisions. The same
derivatives can be used to extrapolate zero density results to finite chemical
potential. We review the recent lattice calculations in the staggered formalism
and discuss its implications to phenomenology and resummed perturbation theory.Comment: 15 pages, 11 figures, The 33rd International Symposium on Lattice
Field Theor
Thermal features far from equilibrium: Prethermalization
The phenomenon of prethermalization and the subsequent steps of
thermalization are analyzed in the framework of the chiral quark model. We
solve the quantum equations of motion of the field theory derived from the 2PI
effective action and study the time scales of equilibration. We find that
already after a 0.6 fm/c long period of time some equilibrium features appear,
even though the system is still far from equilibrium. This might be an
ingredient for understanding the success of ideal hydrodynamic description.Comment: LaTeX, 5 pages. Contribution to the Proceedings of 6th Conference on
Strong and Electroweak Matter 2004 (SEWM04), Helsinki, Finland, 16-19 Jun
200
Range of validity of transport equations
Transport equations can be derived from quantum field theory assuming a loss
of information about the details of the initial state and a gradient expansion.
While the latter can be systematically improved, the assumption about a memory
loss is in general not controlled by a small expansion parameter. We determine
the range of validity of transport equations for the example of a scalar theory. We solve the nonequilibrium time evolution using the three-loop
2PI effective action. The approximation includes off-shell and memory effects
and assumes no gradient expansion. This is compared to transport equations to
lowest order (LO) and beyond (NLO). We find that the earliest time for the
validity of transport equations is set by the characteristic relaxation time
scale , where denotes the on-shell imaginary-part of the self-energy. This
time scale agrees with the characteristic time for partial memory loss, but is
much shorter than thermal equilibration times. For times larger than about
the gradient expansion to NLO is found to describe the ``full''
results rather well for .Comment: 23 latex pages, 9 figure
Semiclassical decay of topological defects
Perturbative estimates suggest that extended topological defects such as cosmic strings emit few particles, but numerical simulations of the fields from which they are constructed suggest the opposite. In this paper we study the decay of the two-dimensional prototype of strings, domain walls in a simple scalar theory, solving the underlying quantum field theory in the Hartree approximation. We conclude that including the quantum effects makes the picture clear: the defects do not directly transform into particles, but there is a nonperturbative channel to microscopic classical structures in the form of propagating waves and persistent localized oscillations, which operates over a huge separation of scales. When quantum effects are included, the microscopic classical structures can decay into particles
Is there a flavor hierarchy in the deconfinement transition of QCD?
We present possible indications for flavor separation during the QCD
crossover transition based on continuum extrapolated lattice QCD calculations
of higher order susceptibilities. We base our findings on flavor specific
quantities in the light and strange quark sector. We propose a possible
experimental verification of our prediction, based on the measurement of higher
order moments of identified particle multiplicities. Since all our calculations
are performed at zero baryochemical potential, these results are of particular
relevance for the heavy ion program at the LHC.Comment: 5 pages, 3 figures, revte
Continuum EoS for QCD with Nf=2+1 flavors
We report on a continuum extrapolated result [arXiv:1309.5258] for the
equation of state (EoS) of QCD with dynamical quark flavors. In this
study, all systematics are controlled, quark masses are set to their physical
values, and the continuum limit is taken using at least three lattice spacings
corresponding to temporal extents up to . A Symanzik improved gauge and
stout-link improved staggered fermion action is used. Our results are available
online [ancillary file to arXiv:1309.5258].Comment: Conference proceedings, 7 pages, 4 figures. Talk presented at 31st
International Symposium on Lattice Field Theory (LATTICE 2013), July 29 -
August 3, 2013, Mainz, German
Static quark-antiquark pair free energy and screening masses: continuum results at the QCD physical point
We study the correlators of Polyakov loops, and the corresponding gauge
invariant free energy of a static quark-antiquark pair in 2+1 flavor QCD at
finite temperature. Our simulations were carried out on = 6, 8, 10, 12,
16 lattices using a Symanzik improved gauge action and a stout improved
staggered action with physical quark masses. The free energies calculated from
the Polyakov loop correlators are extrapolated to the continuum limit. For the
free energies we use a two step renormalization procedure that only uses data
at finite temperature. We also measure correlators with definite Euclidean time
reversal and charge conjugation symmetry to extract two different screening
masses, one in the magnetic, and one in the electric sector, to distinguish two
different correlation lengths in the full Polyakov loop correlator. This
conference contribution is based on the paper: JHEP 1504 (2015) 138Comment: 7 pages, 4 figures. Talk presented at the 33rd International
Symposium on Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe
International Conference Center, Kobe, Japa
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