Frankfurt Institute for Advanced Studies

About: Frankfurt Institute for Advanced Studies is a facility organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Baryon & Quark–gluon plasma. The organization has 798 authors who have published 2733 publications receiving 82799 citations. The organization is also known as: FIAS.

Shear and bulk viscosities of strongly interacting “infinite” parton-hadron matter within the parton-hadron-string dynamics transport approach

Abstract: We study the shear and bulk viscosities of partonic and hadronic matter as functions of temperature $T$ within the parton-hadron-string dynamics (PHSD) off-shell transport approach. Dynamical hadronic and partonic systems in equilibrium are studied by the PHSD simulations in a finite box with periodic boundary conditions. The ratio of the shear viscosity to entropy density $\ensuremath{\eta}(T)/s(T)$ from PHSD shows a minimum (with a value of about $0.1$) close to the critical temperature ${T}_{c}$, while it approaches the perturbative QCD limit at higher temperatures in line with lattice QCD (lQCD) results. For $Tl{T}_{c}$, i.e., in the hadronic phase, the ratio $\ensuremath{\eta}/s$ rises fast with decreasing temperature due to a strong decrease of the entropy density $s$ in the hadronic phase at decreasing $T$. Within statistics, we obtain practically the same results in the Kubo formalism and in the relaxation time approximation. The bulk viscosity $\ensuremath{\zeta}(T)$---evaluated in the relaxation time approach---is found to strongly depend on the effects of mean fields (or potentials) in the partonic phase. We find a significant rise of the ratio $\ensuremath{\zeta}(T)/s(T)$ in the vicinity of the critical temperature ${T}_{c}$, when consistently including the scalar mean-field from PHSD, which is also in agreement with that from lQCD calculations. Furthermore, we present the results for the ratio $(\ensuremath{\eta}+3\ensuremath{\zeta}/4)/s$, which is found to depend nontrivially on temperature and to generally agree with the lQCD calculations as well. Within the PHSD calculations, the strong maximum of $\ensuremath{\zeta}(T)/\ensuremath{\eta}(T)$ close to ${T}_{c}$ has to be attributed to mean-field (or potential) effects that in PHSD are encoded in the temperature dependence of the quasiparticle masses, which is related to the infrared enhancement of the resummed (effective) coupling $g(T)$.

Three-loop HTL gluon thermodynamics at intermediate coupling

Abstract: We calculate the thermodynamic functions of pure-glue QCD to three-loop order using the hard-thermal-loop perturbation theory (HTLpt) reorganization of finite temperature quantum field theory. We show that at three-loop order hard-thermal-loop perturbation theory is compatible with lattice results for the pressure, energy density, and entropy down to temperatures T ≃ 3 Tc. Our results suggest that HTLpt provides a systematic framework that can be used to calculate static and dynamic quantities for temperatures relevant at LHC.

Heavy quark transport in heavy ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider within the UrQMD hybrid model

Abstract: We implement a Langevin approach for the transport of heavy quarks in the ultrarelativistic quantum molecular dynamics (UrQMD) hybrid model, which uses the transport model UrQMD to determine realistic initial conditions for the hydrodynamical evolution of quark gluon plasma and heavy charm and bottom quarks It provides a realistic description of the background medium for the evolution of relativistic heavy ion collisions The diffusion of heavy quarks is simulated with a relativistic Langevin approach, using two sets of drag and diffusion coefficients, one based on a $T$-matrix approach and one based on a resonance model for elastic scattering of heavy quarks within the medium In the case of the resonance model we investigate the effects of different decoupling temperatures of heavy quarks from the medium, ranging between 130 and $180\phantom{\rule{028em}{0ex}}\mathrm{MeV}$ We present calculations of the nuclear modification factor ${R}_{AA}$, as well as of the elliptic flow ${v}_{2}$ in Au + Au collisions at $\sqrt{{s}_{NN}}=200\phantom{\rule{028em}{0ex}}\text{GeV}$ and Pb + Pb collisions at $\sqrt{{s}_{NN}}=276\phantom{\rule{028em}{0ex}}\mathrm{TeV}$ To make our results comparable to experimental data at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC), we implement a Peterson fragmentation and a quark coalescence approach followed by semileptonic decay of the D and B mesons to electrons We find that our results strongly depend on the decoupling temperature and the hadronization mechanism At a decoupling temperature of $130\phantom{\rule{028em}{0ex}}\mathrm{MeV}$ we reach a good agreement with the measurements at both the RHIC and the LHC energies simultaneously for the elliptic flow ${v}_{2}$ and the nuclear modification factor ${R}_{AA}$

Channeling and Radiation in Periodically Bent Crystals

Abstract: Introduction- Related Phenomena- Schemes for Periodic Bending of Crystals- Feasibility of a Positron-Based Crystalline Undulator- Positron-Based CU: Illustrative Material- CUs for Electrons and Heavy Particles- Experimental Studies of CUR - Stimulated Emission from CU- Conclusion - Motion in Periodically Bent Channel- Estimation of the Undulator Parameter due to Channeling- Poschl-Teller Potential- Interplanar Potential within the Moli'ere Approximation- References