Collisional processes of on-shell and off-shell heavy quarks in vacuum and in the Quark-Gluon-Plasma
28 pages, 32 figures ; We study the heavy quark scattering on partons of the quark gluon plasma (QGP) being especially interested in the collisional (elastic) scattering processes of heavy quarks on quarks and gluons. We calculate the different cross...
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28 pages, 32 figures ; We study the heavy quark scattering on partons of the quark gluon plasma (QGP) being especially interested in the collisional (elastic) scattering processes of heavy quarks on quarks and gluons. We calculate the different cross sections for perturbative partons (massless on-shell particles in the vacuum) and for dynamical quasi-particles (off-shell particles in the QGP medium as described by the dynamical quasi-particles model "DQPM") using the leading order Born diagrams. Our results show clearly the effect of a finite parton mass and width on the perturbative elastic $(q(g) Q \rightarrow q (g) Q)$ cross sections which depend on temperature $T$, energy density $\epsilon$, the invariant energy $\sqrt{s}$ and the scattering angle $\theta$. Our detailed comparisons demonstrate that the finite width of the quasi-particles in the DQPM - which encodes the multiple partonic scattering - has little influence on the cross section for $q Q \rightarrow q Q$ as well as $g Q \rightarrow g Q$ scattering except close to thresholds. Thus when studying the dynamics of energetic heavy quarks in a QGP medium the spectral width of the degrees-of-freedom may be discarded. We have, furthermore, compared the cross sections from the DQPM with corresponding results from hard-thermal-loop (HTL) approaches. The HTL inspired models - essentially fixing the regulators by elementary vacuum cross sections and decay amplitudes instead of properties of the QGP at finite temperature - provide quite different results especially w.r.t. the temperature dependence of the $qQ$ and $gQ$ cross sections (in all settings). Accordingly, the transport properties of heavy quarks will be very different as a function of temperature when compared to DQPM results.
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Towards the dynamical study of heavy-flavor quarks in the Quark-Gluon-Plasma
4 pages, 5 figures, International Conference on Strangeness in Quark Matter 2013 (SQM 2013) ; International audience ; Within the aim of a dynamical study of on- and off-shell heavy quarks Q in the quark gluon plasma (QGP) - as produced in...
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4 pages, 5 figures, International Conference on Strangeness in Quark Matter 2013 (SQM 2013) ; International audience ; Within the aim of a dynamical study of on- and off-shell heavy quarks Q in the quark gluon plasma (QGP) - as produced in relativistic nucleus-nucleus collisions - we study the heavy quark collisional scattering on partons of the QGP. The elastic cross sections $\sigma_{q,g-Q}$ are evaluated for perturbative partons (massless on-shell particles) and for dynamical quasi-particles (massive off-shell particles as described by the dynamical quasi-particles model "DQPM") using the leading order Born diagrams. We demonstrate that the finite width of the quasi-particles in the DQPM has little influence on the cross sections $\sigma_{q,g-Q}$ except close to thresholds. We, furthermore, calculate the heavy quark relaxation time as a function of temperature T within the different approaches using these cross sections.
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Transport coefficients from the Nambu-Jona-Lasinio model for $SU(3)_f$
Proceeding of the talk given at SQM2013 in Birmingham, based on arXiv:1305.7180 [hep-ph] ; We calculate the shear $\eta(T)$ and bulk viscosities $\zeta(T)$ as well as the electric conductivity $\sigma_e(T)$ and heat conductivity $\kappa(T)$ within...
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Proceeding of the talk given at SQM2013 in Birmingham, based on arXiv:1305.7180 [hep-ph] ; We calculate the shear $\eta(T)$ and bulk viscosities $\zeta(T)$ as well as the electric conductivity $\sigma_e(T)$ and heat conductivity $\kappa(T)$ within the Nambu-Jona-Lasinio model for 3 flavors as a function of temperature as well as the entropy density $s(T)$, pressure $P(T)$ and speed of sound squared $c_s^2(T)$. We compare the results with other models such as the Polyakov-Nambu-Jona-Lasinio (PNJL) model and the dynamical quasiparticle model (DQPM) and confront these results with lattice QCD data whenever available. We find the NJL model to have a limited predictive power for the thermodynamic variables and various transport coefficients above the critical temperature whereas the PNJL model and DQPM show acceptable results for the quantities of interest.
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Parton-hadron dynamics in heavy-ion collisions
6 pages, 7 figures, Proceedings of the STARS2013 and SMFNS2013 conferences, 4-10 May 2013, Havana/Varadero, Cuba ; The dynamics of partons and hadrons in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String...
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6 pages, 7 figures, Proceedings of the STARS2013 and SMFNS2013 conferences, 4-10 May 2013, Havana/Varadero, Cuba ; The dynamics of partons and hadrons in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for the partonic phase (DQPM) including a dynamical hadronization scheme. The PHSD approach is applied to nucleus-nucleus collisions from low SPS to LHC energies. The traces of partonic interactions are found in particular in the elliptic flow of hadrons and in their transverse mass spectra. We investigate also the equilibrium properties of strongly-interacting infinite parton-hadron matter characterized by transport coefficients such as shear and bulk viscosities and the electric conductivity in comparison to lattice QCD results.
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