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 $g^2 \Phi^4$ 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 $t_{\rm damp} = - 2\omega/\Sigma^{\rm (eq)}_\varrho$, where $-\Sigma^{\rm (eq)}_\varrho/2$ 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 $t_{\rm damp}$ the gradient expansion to NLO is found to describe the ``full'' results rather well for $g^2 \lesssim 1$.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 $N_f=2+1$ 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 $N_t=16$. 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 $N_t$ = 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