We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the Pythia event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM), which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross sections are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into D mesons through coalescence and fragmentation. The hadronized D mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavyquark spin symmetry. Finally, the nuclear modification factor RAA and the elliptic flow v2 of D 0 mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at √ sNN =200 GeV. We find that in the PHSD the energy loss of D mesons at high pT can be dominantly attributed to partonic scattering while the actual shape of RAA versus pT reflects the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the RAA at low pT and enhances the D-meson elliptic flow v2.

International audienceWe derive the relativistic chiral transport equation for massless fermions and antifermions by performing a semiclassical Foldy-Wouthuysen diagonalization of the quantum Dirac Hamiltonian. The Berry connection naturally emerges in the diagonalization process to modify the classical equations of motion of a fermion in an electromagnetic field. We also see that the fermion and antifermion dispersion relations are corrected at first order in the Planck constant by the Berry curvature, as previously derived by Son and Yamamoto for the particular case of vanishing temperature. Our approach does not require knowledge of the state of the system, and thus it can also be applied at high temperature. We provide support for our result by an alternative computation using an effective field theory for fermions and antifermions: the on-shell effective field theory. In this formalism, the off-shell fermionic modes are integrated out to generate an effective Lagrangian for the quasi-on-shell fermions/antifermions. The dispersion relation at leading order exactly matches the result from the semiclassical diagonalization. From the transport equation, we explicitly show how the axial and gauge anomalies are not modified at finite temperature and density despite the incorporation of the new dispersion relation into the distribution function

The drag force and diffusion coefficients for a D meson are calculated in hot dense matter composed of light mesons and baryons, such as it is formed in heavy-ion collisions. We use a unitarized approach based on effective models for the interaction of a D meson with hadrons, which are compatible with chiral and heavy quark symmetries. We study the propagation of the D meson in the hadron matter in two distinct cases. On the one hand, we analyze the propagation of D mesons in matter at vanishing baryochemical potential, which is relevant for high-energetic collisions at LHC or RHIC. On the other hand, we show the propagation of D mesons in the hadronic medium following isentropic trajectories, appropiate at FAIR and NICA heavy-ion experiments. We find a negligible baryon contribution to the transport coefficients at vanishing chemical potential. However at finite baryochemical potential we obtain a large correction to the transport coefficients with the inclusion of nucleons and Delta baryons. The relaxation time for D mesons is reduced a factor 2-3 in the later case, producing a more thermalized D meson-spectrum for FAIR physics than for the typical LHC energies. We finally present results for the spatial diffusion coefficient of a D meson in hadronic matter and the possible existence of a minimum near the phase transition to the quark-gluon plasma at zero and finite baryochemical potential.Comment: 17 pages, 11 figures. One reference added and several typos corrected. This version, which coincides with the published manuscript, includes the Delta baryon vacuum decay constant in the unitarization process. Results do not appreciably change with respect to the first versio

Abstract. We compute the charm drag and diffusion coefficients in a hot pion gas, such as is formed in a Heavy Ion Collision after the system cools sufficiently to transit into the hadron phase. We fully exploit Heavy Quark Effective Theory (with both D and D * mesons as elementary degrees of freedom during the collision) and Chiral Perturbation Theory, and employ standard unitarization to reach higher temperatures. We find that a certain friction and shear diffusion coefficients are almost p 2 -independent at fixed temperature which simplifies phenomenological analysis. At the higher end of reliability of our calculation, T ≃ 150 MeV, we report a charm relaxation length λc ≃ 40 fm, in agreement with the model estimate of He, Fries and Rapp.

We use the recently developed kinetic theory with Berry curvature to describe the fermions and antifermions of a chiral relativistic plasma. We check that this transport approach allows to reproduce the chiral anomaly equation of relativistic quantum field theory at finite temperature. We also check that it allows to describe the anomalous gauge polarization tensor that appears in the Hard Thermal (and/or Dense) effective field theory. We also construct an energy density associated to the gauge collective modes of the chiral relativistic plasma, valid in the case of small couplings or weak fields, which can be the basis for the study of their dynamical evolution.

We study the dynamical evolution of the so-called chiral magnetic effect in an electromagnetic conductor. To this end, we consider the coupled set of corresponding Maxwell and chiral anomaly equations, and we prove that these can be derived from chiral kinetic theory. After integrating the chiral anomaly equation over space in a closed volume, it leads to a quantum conservation law of the total helicity of the system. A change in the magnetic helicity density comes together with a modification of the chiral fermion density. We study in Fourier space the coupled set of anomalous equations and we obtain the dynamical evolution of the magnetic fields, magnetic helicity density, and chiral fermion imbalance. Depending on the initial conditions we observe how the helicity might be transferred from the fermions to the magnetic fields, or vice versa, and find that the rate of this transfer also depends on the scale of wavelengths of the gauge fields in consideration. We then focus our attention on the quark-gluon plasma phase and analyze the dynamical evolution of the chiral magnetic effect in a very simple toy model. We conclude that an existing chiral fermion imbalance in peripheral heavy ion collisions would affect the magnetic field dynamics and, consequently, the charge-dependent correlations measured in these experiments.

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Background: Quantum Chromodynamics is expected to have a phase transition in the same static universality class as the 3D Ising model and the liquid-gas phase transition. The properties of the equation of state, the transport coefficients, and especially the location of the critical point are under intense theoretical investigation. Some experiments are underway, and many more are planned, at high energy heavy ion accelerators.Purpose: Develop a model of the thermal conductivity, which diverges at the critical point, and use it to study the impact of hydrodynamic fluctuations on observables in high energy heavy ion collisions. Methods:We apply mode coupling theory, together with a previously developed model of the free energy that incorporates the critical exponents and amplitudes, to construct a model of the thermal conductivity in the vicinity of the critical point. The effect of the thermal conductivity on correlation functions in heavy ion collisions is studied in a boost invariant hydrodynamic model via fluctuations, or noise.Results: We find that the closer a thermodynamic trajectory comes to the critical point the greater is the magnitude of the fluctuations in thermodynamic variables and in the 2-particle correlation functions in momentum space. Conclusions:It may be possible to discern the existence of a critical point, its location, and thermodynamic and transport properties near to it in heavy ion collisions using the methods developed here.