CARNEGIE MELLON UNIVERSITY -
UNIVERSITY OF PITTSBURGH

Monday, November 23, 2009, Astrophysics Seminar, “The Large Angle Radio—Cosmic Microwave Background Cross-Correlation: What We Expect and What We Actually Find,” Carlos Hernandez Monteagudo, Max-Planck-Institut fur Astrophysik, 2:00 PM, 318 Allen Hall, PITT.

Abstract: I will review the physics of the Integrated Sachs Wolfe effect (ISW) in the context of Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) observations. I will summarise the current observational situation after the analysis of WMAP and LSS surveys and compare it with what is expected from the theoretical side. For that, with the aid of N-body simulations, I will address aspects related to both linear and non-linear ISW theory. I will next show the result of a cross-correlation analysis between WMAP data and the extragalactic radio source catalog of NVSS, where particular emphasis is put on the angular scales where most of the LSS - ISW cross correlation is supposed to arise, and on the impact of the intrinsic radio emission of those sources. My results will show that either we do not understand the redshift distribution of NVSS sources, or the ISW component in WMAP data is far from what the standard LCDM model predicts.

Monday, November 23, 2009, CMU/Pitt Joint Physics Colloquium, "Quark Soup al dente: Applied String Theory" Rob Myers, Perimeter Institute, 4:30 PM, WEH 7500, CMU.

Abstract: In recent years, experiments have discovered an exotic new state of matter known as the strongly coupled quark-gluon plasma (sQGP), which seems to behave like a nearly perfect fluid. At present, it seems that standard theoretical tools, such as perturbation theory and lattice gauge theory, are poorly suited to understand this new phase. At the same time, progress in superstring theory has provided us with a theoretical laboratory for studying the hydrodynamic properties of plasmas in certain strongly interacting gauge theories. This surprising new perspective may allow us to extract the fluid properties of the sQGP from physical processes in a black hole spacetime. Hence we may find the answers to difficult particle physics questions about the sQGP from straightforward calculations in classical general relativity.

Monday, November 30, 2009, CMU/Pitt Joint Physics Colloquium, "Mapping Magnetic Quantization in Real Space in Epitaxial Graphene", Joseph Stroscio, NIST, 4:30 PM, WEH 7500, CMU

Abstract: The cyclotron motion of electrons in a magnetic field has historically been a powerful probe of the Fermi surface properties of metals and two-dimensional electron systems. Oscillations in many measurable properties such as magnetization, thermal conductivity, and resistance, all reflect the quantization of closed orbits and the resulting discrete density of states due to the formation of Landau levels. Here, we show the ability to observe magneto-oscillations in scanning tunneling spectroscopy of epitaxial graphene as a function of both magnetic field and electron energy [1]. These oscillations arise from Landau quantization of the 2-dimensional Dirac electron and hole quasiparticles in the topmost layer of multilayer epitaxial graphene grown on SiC. In normal metals and two dimensional electron gases the Landau levels are equally spaced. In graphene however, the charge carrier velocity is independent of their energy. Consequently, the Landau level energies are not equally spaced and include a new characteristic zero energy state (LL0). Using scanning tunneling spectroscopy of graphene grown on silicon carbide, we directly observe the non-equally spaced Landau level spectrum of graphene, including the four-fold degenerate LL0. Maps of the energy resolved density of states show the distribution of quantum Hall drift states and extended states. We resolve an energy splitting of the LL0 state, which we attribute to the breaking of the valley degeneracy of the LL0 level, and determine its spatial and magnetic field dependence. These splittings are only observed within patches of at least a few magnetic lengths in size, allowing the splitting to turn-on above a critical field.