Thermalization of gluon matter including gg<->ggg interactions

Within a pQCD inspired kinetic parton cascade we simulate the space time evolution of gluons which are produced initially in a heavy ion collision at RHIC energy. The inelastic gluonic interactions $gg \leftrightarrow ggg$ do play an important role: For various initial conditions it is found that thermalization and the close to ideal fluid dynamical behaviour sets in at very early times. Special emphasis is put on color glass condensate initial conditions and the `bottom up thermalization' scenario. Off-equilibrium $3\to 2$ processes make up the very beginning of the evolution leading to an initial decrease in gluon number and a temporary avalanche of the gluon momentum distribution to higher transversal momenta.Comment: 6 pages, 8 figures, Talk given at International Conference on Strong and Electroweak Matter (SEWM 2006), BNL, New York, May 200

Note on counterterms in asymptotically flat spacetimes

We consider in more detail the covariant counterterm proposed by Mann and Marolf in asymptotically flat spacetimes. With an eye to specific practical computations using this counterterm, we present explicit expressions in general $d$ dimensions that can be used in the so-called `cylindrical cut-off' to compute the action and the associated conserved quantities for an asymptotically flat spacetime. As applications, we show how to compute the action and the conserved quantities for the NUT-charged spacetime and for the Kerr black hole in four dimensions.Comment: 13 pages, v. 2 added reference

Vortex stability in nearly two-dimensional Bose-Einstein condensates with attraction

We perform accurate investigation of stability of localized vortices in an effectively two-dimensional ("pancake-shaped") trapped BEC with negative scattering length. The analysis combines computation of the stability eigenvalues and direct simulations. The states with vorticity S=1 are stable in a third of their existence region, $0<N<(1/3)N_{\max}^{(S=1)}$, where $N$ is the number of atoms, and $N_{\max}^{(S=1)}$ is the corresponding collapse threshold. Stable vortices easily self-trap from arbitrary initial configurations with embedded vorticity. In an adjacent interval, $(1/3)N_{\max }^{(S=1)}<N<$ $\allowbreak 0.43N_{\max}^{(S=1)}$, the unstable vortex periodically splits in two fragments and recombines. At $N>$ $\allowbreak 0.43N_{\max}^{(S=1)}$, the fragments do not recombine, as each one collapses by itself. The results are compared with those in the full 3D Gross-Pitaevskii equation. In a moderately anisotropic 3D configuration, with the aspect ratio $\sqrt{10}$, the stability interval of the S=1 vortices occupies $\approx 40$ of their existence region, hence the 2D limit provides for a reasonable approximation in this case. For the isotropic 3D configuration, the stability interval expands to 65% of the existence domain. Overall, the vorticity heightens the actual collapse threshold by a factor of up to 2. All vortices with $S\geq 2$ are unstable.Comment: 21 pages, 8 figures, to appear in Physical Review

A user-centric execution environment for <em>CineGrid</em> workloads

The abundance and heterogeneity of IT resources available, together with the ability to dynamically scale applications poses significant usability issues to users. Without understanding the performance profile of available resources users are unable to efficiently scale their applications in order to meet performance objectives. High quality media collaborations, like CineGrid, are one example of such diverse environments where users can leverage dynamic infrastructures to move and process large amounts of data. This paper describes our user-centric approach to executing high quality media processing workloads over dynamic infrastructures. Our main contribution is the CGtoolkit environment, an integrated system which aids users cope with the infrastructure complexity and large data sets specific to the digital cinema domain

40 Gigabit ethernet: prototyping transparent end-to-end connectivity

The ever increasing demands of data intensive eScience applications have pushed the limits of computer networks. With the launch of the new 40 Gigabit Ethernet (40GE) standard, 802.3ba, applications can go beyond the common 10 Gigabit/s per data stream barrier for both local area, and as demonstrated in the GLIF 2010 and Supercomputing 2010 demos [3], wide area setups. In this article we profile the performance of state-of-the-art server hardware combined with 40GE technology. We give an insight on the issues involved with ultra high performance network adapters and suggest optimization approaches

Direct photons in Pb+Pb at CERN-SPS from microscopic transport theory

Direct photon production in central Pb+Pb collisions at CERN-SPS energy is calculated within the relativistic microscopic transport model UrQMD, and within distinctly different versions of relativistic hydrodynamics. We find that in UrQMD the local momentum distributions of the secondaries are strongly elongated along the beam axis initially. Therefore, the pre-equilibrium contribution dominates the photon spectrum at transverse momenta above $\approx 1.5$ GeV. The hydrodynamics prediction of a strong correlation between the temperature and radial expansion velocities on the one hand and the slope of the transverse momentum distribution of direct photons on the other hand thus is not recovered in UrQMD. The rapidity distribution of direct photons in UrQMD reveals that the initial conditions for the longitudinal expansion of the photon source (the meson ``fluid'') resemble rather boostinvariance than Landau-like flow.Comment: 14 pages, RevTex, 5 Encapsulated-PostScript Figure

KNO scaling of fluctuations in pp and pA, and eccentricities in heavy-ion collisions

Multiplicity fluctuations at midrapidity in p+p collisions at high energies are described by a negative binomial distribution and exhibit approximate Koba-Nielsen-Olesen (KNO) scaling. We find that these KNO fluctuations are important also for reproducing the multiplicity distribution in d+Au collisions observed at RHIC, adding to the Glauber fluctuations of the number of binary collisions or participants. We predict that the multiplicity distribution in p+Pb collisions at the LHC also deviates little from the KNO scaling function. Finally, we analyze various moments of the eccentricity of the particle production zone in A+A collisions at RHIC and LHC and find that particle production fluctuations increase fluctuation dominated moments such as the triangularity epsilon_3 substantially.Comment: 7 pages, 6 figures; v2: updated references and a few minor modifications, to appear in PR