Quark Number Susceptibility in Hard Thermal Loop Approximation

We calculate the quark number susceptibility in the deconfined phase of QCD using the hard thermal loop (HTL) approximation for the quark propagator. 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 spacelike 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 that of free one around the critical temperature but approaches free results at infinite temperature limit. The results are in conformity with recent lattice calculations.Comment: 9 pages including four figures and this version is accepted for publication in Euro. Phys. J.

Energy gain of heavy quarks by fluctuations in the QGP

The collisional energy gain of a heavy quark due to chromo-electromagnetic field fluctuations in a quark-gluon plasma is investigated. The field fluctuations lead to an energy gain of the quark for all temperatures and velocities. The net effect is a reduction of the collisional energy loss by 15-40% for parameters relevant at RHIC energies.Comment: 6 pages, 4 figures, extended version, accepted for publication in Phys. Rev.

Molecular Dynamics Studies of Organic-Coated Nano Aerosols

Atmospheric aerosols play an important role in atmospheric processes. These aerosol particles can affect climate through scattering, transmission and absorption of radiation as well as acting as cloud condensation nuclei. It has recently been found that fatty acids reside on the surfaces of marine and continental aerosols. In this research, an attempt has been made to understand the structures and properties of such organic coated aerosols using Molecular Dynamics simulation. The model particle consisted of a water droplet coated with fatty acid. The density profile (using both Coarse-Grained and Atomistic/United atom models) demonstrated that such aerosol particles have an inverted micelle structure consisting of an aqueous core and with the hydrophobic hydrocarbon tails exposed to the atmosphere. For smaller chains, with the organic molecules directed radially outwards from the water - organic interface) the normal pressure profile showed that the organic coating is under tension resulting in a 'negative' surface tension. As a result, such particles would have an inverse Kelvin vapor pressure effect and would be able to process water vapor despite the hydrophobic surface. Following the work on surface tension, the rate of water uptake by coated aerosols was computed. It was found that the sticking coefficient of water vapor on such particles was about a sixth of that on pure water droplets. This may seem to imply that the net condensation rate is lower, but we also need to take into account the evaporation of water from such particles. With a significant reduction in the evaporation rate (the coating lends greater stability to the particle resulting in reduced evaporation rate), the equilibrium vapor pressure of water on such particles reduced, resulting in a "net water attractor". Thus if such structures were created in sufficient concentration, they might be important contributors in the cloud condensation process. Next the effect of longer Fatty acid molecules and branched surfactants on the structure and properties of coated particles was studied. It was found that in either case, due to stronger organic - organic interactions, the surfactant molecules tend to align themselves parallel to each other forcing local flattening of the underlying water substrate and consequently such particles behaved in a manner consistent with an "oily" drop, in sharp contrast to the case of shorter chains, where the particle was a "net water attractor". Finally, the effect of organic coating on the Stokes drag of functionalized nanoparticles was studied. This work was motivated by a recent experimental study in which the thickness of Self Assembled Monolayers on Gold nanoparticles was characterized using a measurement process that relies on the determination of the size of a charged particle through knowledge of the drag force. The thickness of the coating was found to ~35% less than that predicted by a rigid core-shell model. This suggests that the functionalized Au-NP would have an inverted micelle structure. The MD simulations showed that the drag on the coated particle was indeed less than that on the corresponding pure particle, consistent with the experimental observation

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.Comment: 16 pages, 4 figures, high resolution figures available from the authors, final version to be published in J. Phys.

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.Comment: Accepted in PR

D=2 gluon condensate and QCD propagators at finite temperature

We calculate the dimension two gluon condensate contribution to quark, gluon and ghost propagators at finite temperature.Comment: Minor modifications. Accepted in PL

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 the semi-classical transport theory. An anisotropic potential showing a minimum in the direction of the parton velocity is found. As consequences possible new bound states and J/psi dissociation are discussed.Comment: 4 pages, 2 figures, final, extended version, to be published in Phys.Rev.

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 space like 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.Comment: 20 pages, 14 figures (high resolution figures available with authors); version accepted for publication in Phys. Rev.

Chiral Susceptibility in Hard Thermal Loop Approximation

The static and dynamic chiral susceptibilities in the quark-gluon plasma are calculated within the lowest order perturbative QCD at finite temperature and the Hard Thermal Loop resummation technique using an effective quark propagator. After regularisation of ultraviolet divergences, the Hard Thermal Loop results are compared to QCD lattice simulations.Comment: 12 pages, 4 figures, revised version, to be published in Phys. Rev.