Purnendu Chakraborty

Quasiparticle theory of shear and bulk viscosities of hadronic matter

A theoretical framework for the calculation of shear and bulk viscosities of hadronic matter at finite temperature is presented. The framework is based on the quasiparticle picture. It allows for an arbitrary number of hadron species with pointlike interactions, and allows for both elastic and inelastic collisions. Detailed balance is ensured. The particles have temperature-dependent masses arising from mean-field or potential effects, which maintains self-consistency between the equation of state and the transport coefficients. As an example, we calculate the shear and bulk viscosity in the linear {sigma} model. The ratio of shear viscosity to entropy density shows a minimum in the vicinity of a rapid crossover transition, whereas the ratio of bulk viscosity to entropy density shows a maximum.

Quark number susceptibility in hard thermal loop approximation

Abstract. We calculate the quark number susceptibility in the deconfined phase of QCD using the hard thermal loop (HTL) approximation for the quark propagator and quark–meson vertices. This improved perturbation theory takes into account important medium effects such as thermal quark masses and Landau damping in the quark–gluon plasma. We explicitly show that the Landau damping part in the quark propagator for space-like quark momenta does not contribute to the quark number susceptibility due to the quark number conservation. We find that the quark number susceptibility only due to the collective quark modes deviates from the free one around the critical temperature but approaches free results in the infinite temperature limit. The results are in conformity with recent lattice calculations.

Wakes in the quark-gluon plasma

Using the high temperature approximation we study, within the linear response theory, the wake in the quark-gluon plasma by a fast parton owing to dynamical screening in the spacelike region. When the parton moves with a speed less than the average speed of the plasmon, we find that the wake structure corresponds to a screening charge cloud traveling with the parton with one sign flip in the induced charge density resulting in a Lennard-Jones type potential in the outward flow with a short range repulsive and a long range attractive part. On the other hand if the parton moves with a speed higher than that of plasmon, the wake structure in the induced charge density is found to have alternate sign flips and the wake potential in the outward flow oscillates analogous to Cerenkov-like wave generation with a Mach cone structure trailing the moving parton. The potential normal to the motion of the parton indicates a transverse flow in the system. We also calculate the potential due to a color dipole and discuss consequences of possible new bound states and J/{psi} suppression in the quark-gluon plasma.

Quark-number susceptibility, thermodynamic sum rule, and the hard thermal loop approximation

The quark number susceptibility, associated with the conserved quark number density, is closely related to the baryon and charge fluctuations in the quark-gluon plasma, which might serve as signature for the quark-gluon plasma formation in ultrarelativistic heavy-ion collisions. In addition to QCD lattice simulations, the quark number susceptibility has been calculated recently using a resummed perturbation theory (hard thermal loop resummation). In the present work we show, based on general arguments, that the computation of this quantity neglecting hard thermal loop vertices contradicts the Ward identity and violates the thermodynamic sum rule following from quark number conservation. We further show that the hard thermal loop perturbation theory is consistent with the thermodynamic sum rule.

Chiral susceptibility in the hard thermal loop approximation

The static and dynamic chiral susceptibilities in the quark-gluon plasma are calculated within lowest order perturbative QCD at finite temperature and the hard thermal loop resummation technique using an effective quark propagator. After regularization of ultraviolet divergences, the hard thermal loop results are compared to QCD lattice simulations.

Screening of a moving parton in the quark-gluon plasma

The screening potential of a parton moving through a quark-gluon plasma is calculated using semiclassical transport theory. An anisotropic potential showing a minimum in the direction of the parton velocity is found. As consequences possible new bound states in the quark-gluon plasma and J/{psi} dissociation are discussed.

Wakes in a collisional quark-gluon plasma

Wakes created by a parton moving through a static and infinitely extended quark?gluon plasma are considered. In contrast to former investigations, collisions within the quark?gluon plasma are taken into account using a transport theoretical approach (Boltzmann equation) with a Bhatnagar?Gross?Krook collision term. Within this model, it is shown that the wake structure changes significantly compared to the collisionless case.

Screening masses in gluonic plasma

Both electric and magnetic screening masses in a nonperturbative gluonic background are investigated using operator product expansion. The magnetic screening mass is found to agree with lattice results whereas the electric screening mass is somewhat smaller than the one found on the lattice.

Energy gain of heavy quarks by fluctuations in a quark-gluon plasma

The collisional energy gain of a heavy quark due to chromoelectromagnetic field fluctuations in a quark-gluon plasma is investigated. The field fluctuations lead to an energy gain of the quark for all velocities. The net effect is a reduction of the collisional energy loss by 15-40% for parameters relevant at RHIC energies.

D=2 gluon condensate and QCD propagators at finite temperature

Abstract We calculate the dimension two gluon condensate contribution to quark, gluon and ghost propagators at finite temperature.