Transport coefficients of a unitarized pion gas

The latest experimental results in relativistic heavy-ion collisions show that the matter there produced requires transport coefficients because of the important collective properties found. We review the theoretical calculation of these transport coefficients in the hadron side at low temperatures by computing them in a gas composed of low energy pions. The interaction of these pions is taken from an effective chiral theory and further requiring scattering unitarity. The propagation of D and D* mesons in the thermalized pion gas is also studied in order to extract the heavy quark diffusion coefficients in the system.Comment: 7 pages, 3 figures, contribution to the International School of Nuclear Physics, 33rd Course: From Quarks and Gluons to Hadrons and Nuclei, Erice-Sicily: 16-24 September 201

Hydrodynamics and the Detection of the QCD Axial Anomaly in Heavy Ion Collisions

We consider the experimental implications of the axial current triangle diagram anomaly in a hydrodynamic description of high density QCD. We propose a signal of an enhanced production of spin-excited hadrons in the direction of the rotation axis in off-central heavy ion collisions.Comment: 15 pages, 19 figures; v2: refs added, minor changes to the plots; v3, comments adde

Flow fluctuations and long-range correlations: elliptic flow and beyond

These proceedings consist of a brief overview of the current understanding of collective behavior in relativistic heavy-ion collisions. In particular, recent progress in understanding the implications of event-by-event fluctuations have solved important puzzles in existing data -- the "ridge" and "shoulder" phenomena of long-range two-particle correlations -- and have created an exciting opportunity to tightly constrain theoretical models with many new observables.Comment: 10 pages, 2 figures, Proceedings for the 22nd International Conference On Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2011), Annecy, France, May 23 - 28, 2011; includes Fig. 2 which was omitted from journal submission for lack of spac

Universal parameterization of initial-state fluctuations and its applications to event-by-event anisotropy

We propose Elliptic Power and Power parameterizations for the probability distribution of initial state anisotropies in heavy-ion collisions. By assuming a linear eccentricity scaling, the new parameterizations can also be applied to fluctuations of harmonic flow. In particular, we analyze flow multi-particle cumulants and event-by-event distributions, both of which are recently measured at the LHC.Comment: 4 pages and 3 figures, proceedings of the XXIV Quark Matter conference, May 19-24 2014, Darmstadt (Germany

Two-component liquid model for the quark-gluon plasma

We consider a two-component-liquid model, a la Landau, for the quark-gluon plasma. Qualitatively, the model fits well some crucial observations concerning the plasma properties. Dynamically, the model assumes the existence of an effective scalar field which is condensed. The existence of such a condensate is supported by lattice data. We indicate a possible crucial test of the model by lattice simulations.Comment: 5 pages; Talk given by V.I. Zakharov at 16th International Seminar on High Energy Physics (QUARKS-2010), Kolomna, Russia, 6-12 June, 201

Hydrodynamic predictions for mixed harmonic correlations in 200 GeV Au+ Au collisions

Recent measurements at the Large Hadron Collider involve the correlation of different azimuthal flow harmonics vn. These new observables add constraints to theoretical models and probe aspects of the system that are independent of traditional single-harmonic measurements such as two-particle and multiparticle cumulants vn{m}. Many of these new observables have not yet been measured at the Relativistic Heavy Ion Collider (RHIC), leaving an opportunity to make predictions as a test of models across energies. We make predictions using NEXSPHERIO, a hydrodynamical model which has accurately reproduced a large set of single-harmonic correlations in a large range of transverse momenta and centralities at RHIC. Our predictions thus provide an important baseline for comparison to correlations of flow harmonics, which contain nontrivial information about the initial state as well as quark-gluon plasma transport properties. We also point out significant biases that can appear when using wide centrality bins and nontrivial event weighting, necessitating care in performing experimental analyses and in comparing theoretical calculations to these measurements

Charged particle directed flow in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV measured with ALICE at the LHC

Charged particle directed flow at midrapidity, |eta|<0.8, and forward rapidity, 1.7 < |eta|<5.1, is measured in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV with ALICE at the LHC. Directed flow is reported as a function of collision centrality, charged particle transverse momentum, and pseudo-rapidity. Results are compared to measurements at RHIC and recent model calculations for LHC energies.Comment: Talk given at the XXII International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2011), 23-28 May 2011, Annecy, France; 4 pages, 3 figure

Chiral restoration effects on the shear viscosity of a pion gas

We investigate the shear viscosity of a pion gas in relativistic kinetic theory, using the Nambu-Jona-Lasinio model to construct the pion mass and the pi-pi interaction at finite temperature. Whereas at low temperatures the scattering properties and, hence, the viscosity are in agreement with lowest-order chiral perturbation theory, we find strong medium modifications in the crossover region. Here the system is strongly coupled and the scattering lengths diverge, similarly as for ultra-cold Fermi gases at a Feshbach resonance. As a consequence, the ratio eta/s is found to be strongly reduced as compared to calculations without medium-modified masses and scattering amplitudes. However, the quantitative results are very sensitive to the details of the applied approximations.Comment: 15 pages, 12 figures; v2: extended discussions of the dressed sigma propagator and the low-temperature limit, typos corrected, accepted versio

Elliptic flow in proton-proton collisions at 7 TeV

The angular correlations measured in proton-proton collisions at 7 TeV are decomposed into contributions from back to back emission and elliptic flow. Modeling the dominant term in the correlation functions as a momentum conservation effect or as an effect of the initial transverse velocity of the source, the remaining elliptic flow component can be estimated. The elliptic flow coefficient extracted from the CMS Collaboration data is 0.04-0.08. No additional small-angle, ridge-like correlations are needed to explain the experimental data