Qualitative and Quantitative Jet Physics in Pb + Pb at LHC

The momentum dependence of the exciting new Pb + Pb data from LHC qualitatively suggests a perturbative picture interpretation for the energy loss of high-pT particles, but conclusions are difficult to draw due to the lack of 1) a quantitative theoretical calculation constrained by current high precision RHIC data and 2) a lack of control p + p and p + Pb data at LHC. Future measurements of identified heavy quark suppression will provide a novel qualitative tool for determining the dominant physics of the quark-gluon plasma created at RHIC and LHC.Comment: 5 pages, 3 figures, proceedings for the Kruger2010 Workshop on Discovery Physics at LH

A New Class of Exact Solutions in String Theory

We prove that a large class of leading order string solutions which generalize both the plane-wave and fundamental string backgrounds are, in fact, exact solutions to all orders in \alpha'. These include, in particular, the traveling waves along the fundamental string. The key features of these solutions are a null symmetry and a chiral coupling of the string to the background. Using dimensional reduction, one finds that the extremal electric dilatonic black holes and their recently discovered generalizations with NUT charge and rotation are also exact solutions. We show that our bosonic solutions are also exact solutions of the heterotic string theory with no extra gauge field background.Comment: 38 pages, harvmac, Imperial/TP/93-94/54, UCSBTH-94-31 Major revision of Section 6 (heterotic string solutions: no gauge field background is needed) and extension of Appendix A (special holonomy, parallelizable spaces and relation to WZW models based on non-semisimple groups

Strong-coupling Jet Energy Loss from AdS/CFT

We propose a novel definition of a holographic light hadron jet and consider the phenomenological consequences, including the very first fully self-consistent, completely strong-coupling calculation of the jet nuclear modification factor $R_{AA}$, which we find compares surprisingly well with recent preliminary data from LHC. We show that the thermalization distance for light parton jets is an extremely sensitive function of the \emph{a priori} unspecified string initial conditions and that worldsheets corresponding to non-asymptotic energy jets are not well approximated by a collection of null geodesics. Our new string jet prescription, which is defined by a separation of scales from plasma to jet, leads to the re-emergence of the late-time Bragg peak in the instantaneous jet energy loss rate; unlike heavy quarks, the energy loss rate is unusually sensitive to the very definition of the string theory object itself. A straightforward application of the new jet definition leads to significant jet quenching, even in the absence of plasma. By renormalizing the in-medium suppression by that in the vacuum we find qualitative agreement with preliminary CMS $R_{AA}^{jet}(p_T)$ data in our simple plasma brick model. We close with comments on our results and an outlook on future work.Comment: 28 pages, 9 figure

On exact solutions and singularities in string theory

We construct two new classes of exact solutions to string theory which are not of the standard plane wave or gauged WZW type. Many of these solutions have curvature singularities. The first class includes the fundamental string solution, for which the string coupling vanishes near the singularity. This suggests that the singularity may not be removed by quantum corrections. The second class consists of hybrids of plane wave and gauged WZW solutions. We discuss a four dimensional example in detail.Comment: 45 pages, harvmac, Imperial/TP/93-94/38, NI94004 (minor corrections

A Framework for Robust Assimilation of Potentially Malign Third-Party Data, and its Statistical Meaning

This paper presents a model-based method for fusing data from multiple sensors with a hypothesis-test-based component for rejecting potentially faulty or otherwise malign data. Our framework is based on an extension of the classic particle filter algorithm for real-time state estimation of uncertain systems with nonlinear dynamics with partial and noisy observations. This extension, based on classical statistical theories, utilizes statistical tests against the system's observation model. We discuss the application of the two major statistical testing frameworks, Fisherian significance testing and Neyman-Pearsonian hypothesis testing, to the Monte Carlo and sensor fusion settings. The Monte Carlo Neyman-Pearson test we develop is useful when one has a reliable model of faulty data, while the Fisher one is applicable when one may not have a model of faults, which may occur when dealing with third-party data, like GNSS data of transportation system users. These statistical tests can be combined with a particle filter to obtain a Monte Carlo state estimation scheme that is robust to faulty or outlier data. We present a synthetic freeway traffic state estimation problem where the filters are able to reject simulated faulty GNSS measurements. The fault-model-free Fisher filter, while underperforming the Neyman-Pearson one when the latter has an accurate fault model, outperforms it when the assumed fault model is incorrect.Comment: IEEE Intelligent Transportation Systems Magazine, special issue on GNSS-based positionin