Testing the Space-Time Structure of Event Generators

We report on work done in collaboration with Klaus Kinder-Geiger and John Ellis which aims at connecting the space-time structure of event generator simulations with observable output.Comment: 16 pages LaTeX, including 5 postscript figures. To appear in the Proceedings of ``RHIC Physics and Beyond - Kay Kay Gee Day'' (Brookhaven National Laboratory, 23 Oct 1998), ed. by B. Muller and R.D. Pisarski, AIP Conference Proceeding

Equation of State and Collective Dynamics

This talk summarizes the present status of a program to quantitatively relate data from the Relativistic Heavy Ion Collider (RHIC) on collective expansion flow to the Equation of State (EOS) of hot and dense strongly interacting matter, including the quark-gluon plasma and the quark-hadron phase transition. The limits reached with the present state of the art and the next steps required to make further progress will both be discussed.Comment: 8 pages, 6 two-part figures. Invited talk given at the 5th International Conference on the Physics and Astrophysics of Quark-Gluon Plasma (ICPAQGP 2005), Kolkata (India), Feb 8-12, 2005. Proceedings to be published in Journal of Physics: Conference Series (Jan-E Alam et al., eds.

The Non-Linear Dependence of Flux on Black Hole Mass and Accretion Rate in Core Dominated Jets

We derive the non-linear relation between the core flux F_{nu} of accretion powered jets at a given frequency and the mass M of the central compact object. For scale invariant jet models, the mathematical structure of the equations describing the synchrotron emission from jets enables us to cancel out the model dependent complications of jet dynamics, retaining only a simple, model independent algebraic relation between F_{nu} and M. This approach allows us to derive the F_{nu}-M relation for any accretion disk scenario that provides a set of input boundary conditions for the magnetic field and the relativistic particle pressure in the jet, such as standard and advection dominated accretion flow (ADAF) disk solutions. Surprisingly, the mass dependence of F_{nu} is very similar in different accretion scenarios. For typical flat-spectrum core dominated radio jets and standard accretion scenarios we find F_{nu}~M^{17/12}. The 7-9 orders of magnitude difference in black hole mass between microquasars and AGN jets imply that AGN jets must be about 3-4 orders of magnitude more radio loud than microquasars, i.e., the ratio of radio to bolometric luminosity is much smaller in microquasars than in AGN jets. Because of the generality of these results, measurements of this F_{nu}-M dependence are a powerful probe of jet and accretion physics. We show how our analysis can be extended to derive a similar scaling relation between the accretion rate mdot and F_{nu} for different accretion disk models. For radiatively inefficient accretion modes we find that the flat spectrum emission follows F_{nu}~(mdot*M)^{17/12}.Comment: Added key words and acknowledgements, minor editorial corrections. 6 pages, to appear in MNRAS 343, L59-L6

ken

From the beginning, the world of game-playing by machine has been fortunate in attracting contributions from the leading names of computer science. Charles Babbage, Konrad Zuse, Claude Shannon, Alan Turing, John von Neumann, John McCarthy, Alan Newell, Herb Simon and Ken Thompson all come to mind, and each reader will wish to add to this list. Recently, the Journal has saluted both Claude Shannon and Herb Simon. Ken’s retirement from Lucent Technologies’ Bell Labs to the start-up Entrisphere is also a good moment for reflection

The Challenge of Reforming the WTO Dispute Settlement Understanding

The May 2003 deadline for the completion of the negotiations on improvements and clarifications of the Dispute Settlement Understanding (DSU) under the Doha Mandate has not been met. However, Members agreed in July 2003 to extend the deadline for the review until the end of May 2004. This article briefly summarises the past six years of negotiations on the DSU review, the most contentious issues and the systemic difficulties of the negotiations. We conclude with prospects for the forthcoming negotiations until 2004.WTO Dispute Settlement Understanding DSU Review

Effects of jet quenching on the hydrodynamical evolution of quark-gluon plasma

We study the effects of jet quenching on the hydrodynamical evolution of the quark-gluon plasma (QGP) fluid created in a heavy-ion collision. In jet quenching, a hard QCD parton, before fragmenting into a jet of hadrons, deposits a fraction of its energy in the medium, leading to suppressed production of high-pT hadrons. Assuming that the deposited energy quickly thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP fluid. For partons moving at supersonic speed, v_p > c_s, and sufficiently large energy loss, a shock wave forms leading to conical flow [1]. The PHENIX Collaboration recently suggested that observed structures in the azimuthal angle distribution [2] might be caused by conical flow. We show here that conical flow produces different angular structures than predicted in [1] and that, for phenomenologically acceptable values of parton energy loss, conical flow effects are too weak to explain the structures seen by PHENIX [2].Comment: 4 pages, 3 figures. Last figure changed, now showing angular distribution of pions instead of photons. Added comments on "lost jets" and pT-dependence of angular correlation

Formation of recollimation shocks in jets of high-mass X-ray binaries

We study conditions for formation of recollimation shocks in jets interacting with stellar winds in high-mass X-ray binaries. We show the existence of a critical jet power, dependent on the wind rate and velocity and the jet velocity, above which a recollimation shock is not formed. For jet powers below critical, we derive the location of the shock. We show that surface shocks may still exist above the critical power, but only occupy a small volume of the jet and do not significantly alter the jet opening angle. We test these prediction by 3-D numerical simulations, which confirm the existence and the value of the critical power. We apply our results to Cyg X-1 and Cyg X-3.Comment: MNRAS, in pres

Elliptic flow in 200 A GeV Au+Au collisions and 2.76 A TeV Pb+Pb collisions: insights from viscous hydrodynamics + hadron cascade hybrid model

Using the newly developed hybrid model VISHNU which connects viscous hydrodynamics with a hadron cascade model, we study the differential and integrated elliptic flow v_2 at different centrality bins for 200 A GeV Au+Au collisions and 2.76 A TeV Pb+Pb collisions. We find that the average Quark Gluon Plasma (QGP) specific shear viscosity eta/s slightly increases from Relativistic Heavy Ion Collider (RHIC) to Large Hadron Collider (LHC) energies. However, a further study assuming different temperature dependencies for (eta/s)_QGP shows that one cannot uniquely constrain the form of (eta/s)_QGP(T) by fitting the spectra and v_2 alone. Based on our current understanding, the question on whether the QGP fluid is more viscous or more perfect in the temperature regime reached by LHC energies is still open.Comment: added a figure and discussion; this version accepted by Phys. Rev.

A deep Chandra observation of Abell 4059: a new face to radio-mode AGN feedback?

A deep Chandra observation of the cooling core cluster Abell 4059 (A4059) is presented. Previous studies have found two X-ray cavities in the central regions of A4059 together with a ridge of X-ray emission 20kpc south-west of the cluster center. These features are clearly related to the radio galaxy PKS2354-35 which resides in the cD galaxy. Our new data confirm these previous findings and strengthen previous suggestions that the south-western ridge is colder and denser than, but in approximate pressure equilibrium with, the surrounding ICM atmosphere. In addition, we find evidence for a weak shock that wraps around the north and east sides of the cavity structure. Our data allow us to map the 2-dimensional distribution of metals in the ICM of A4059 for the first time. We find that the SW ridge possesses an anomalously high (super-solar) metalicity. The unusual morphology, temperature structure and metal distribution all point to significant asymmetry in the ICM atmosphere prior to the onset of radio-galaxy activity. Motivated by the very high metalicity of the SW ridge, we hypothesize that the ICM asymmetry was caused by the extremely rapid stripping of metal enriched gas from a starburst galaxy that plunged through the core of A4059. Furthermore, we suggest that the onset of powerful radio-galaxy activity in the cD galaxy may have been initiated by this starburst/stripping event, either via the tidal-shocking of cold gas native to the cD galaxy, or the accretion of cold gas that had been stripped from the starburst galaxy.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 11 figures. A version of this paper including full resolution figures can be found at http://www.astro.umd.edu/~chris/publications/papers/a4059_2008.pd