April 3, 2002 | 3:30 PM | RI 480 | Wednesday colloquium MHD Turbulence: Scaling, Anisotropy, New Regimes Alex Lazarian, University of Wisconsin
April 10, 2002 | 3:30 PM | RI 480 | Wednesday colloquium LISA: Listening to Gravitational Waves from Space Bernard Schutz,
The LISA gravitational wave space observatory is a joint mission between NASA and ESA, scheduled to launch in 2011. It will open up the low-frequency gravitational wave window, observing supermassive black holes in distant galaxies and binary star systems in the Milky Way. Its goals include probing the earliest phases of galaxy formation, testing general relativity and the no-hair theorem for black holes, positively identifying black holes, and possibly even measuring the acceleration history of the universe to high redshift. Unlike ground-based detectors, it will make observations of such sensitivity that it will be limited more by backgrounds of gravitational waves produced by distant sources than by instrumental noise. LISA technology presents challenges that have not been met in space before the critical components will be tested in space in 2006. The talk will cover all aspects of LISA's design concept and scientific mission.
April 17, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Black Holes: Demographics and Galaxy Evolution David Merritt, Rutgers University
April 24, 2002 | 3:30 PM | RI 480 | Wednesday colloquium CMB Anisotropy: Status and Prospects Lyman Page, Princeton University
May 1, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Plasma Turbulence in the Solar Wind and in the Galaxy Stephen Spangler, University of Iowa
May 8, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Looking Beyond the Big Bang Paul Steinhardt, Princeton University
The conventional picture of cosmic evolution, a combination of the big bang model and the inflationary scenario, assumes that the big bang is the beginning of space time. This talk will discuss a radical alternative, the "cyclic universe," based on the concept of an eternal universe with an endless sequence of expansions and contractions. We will discuss how the problems of earlier cyclic models can be avoided and how all of the successful predictions of the conventional picture can be reproducedby events before the big bang without having a period of inflation.
May 22, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Analysis Issues for CMB Anisotropies Ben Wandelt, University of Illinois
May 29, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Principles of Electricity and Magnetism with Applications to Quasars, Pulsars, and Gamma Ray Bursts Roger Blandford, CalTech
March 29, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Extreme Astronomy: Neutrinos from Beyond the Edge Peter Gorham,
Single cosmic-ray particles of Joule-scale energies--a billion times higher than the strongest earth-based accelerators can produce--are peppering earth at a rate of several tens of thousands per day, apparently in defiance of the so-called Greisen-Zatsepin-Kuzmin (GZK) cutoff. This GZK cutoff is actually a kind of absorption edge in the cosmic ray spectrum: if these particles originate at distances large compared to a few Mpc, then they should be scattered and absorbed by the cosmic microwave background, which appear as gamma-rays in the rest frame of the particles. Such scattering must in turn yield pions and thus neutrinos, and these high energy GZK neutrinos are perhaps the clearest signature of the cosmic-ray scattering process from which they arise. Their detection, however, is a difficult and compelling challenge, requiring targets of tens to hundreds of cubic km of water-equivalent fiducial mass and several years of operation. We discuss a series of new initiatives aimed at discovering the GZK neutrinos, exploiting the Askaryan effect: strong coherent radio emission from high energy cascades in solid dielectric media such as natural ice and rock salt. This process, which dominates the secondary emission from particle showers at PeV energies and above, may provide the most cost-effective and direct approach to instrumenting the huge volumes necessary for GZK neutrino physics.
April 5, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Imaging the Early Universe with ACBAR Bill Holzapfel, University of Berkeley
Primary anisotropies of the Cosmic Microwave Background (CMB) encode a wealth of information about the early Universe. Recent degree-scale experiments have begun to exploit the potential of the CMB as a precision probe of cosmology with encouraging results. High resolution images of primary anisotropies can be used to produce improved constraints on cosmological parameters. In addition, the interaction of the CMB with intervening matter can produce secondary anisotropies that exhibit a sensitive dependence on the growth of structure. I will discuss the potential of high resolution observations of the CMB as a cosmological probe and the new generation of experiments designed for this task. In particular, I will focus on the Arcminute Cosmology Bolometer Array Receiver (ACBAR) which is now beginning its second season of observations at the South Pole.
April 12, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Small Experiments, High Precision and Some Large Questions Norval Fortson, University of Washington
April 19, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Update on the EDGE LDB Project Stephan Meyer, The University of Chicago
April 26, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Angular Power Spectrum of the Sunyaev-Zel'dovich Effect Eiichiro Komatsu, Princeton University
Measurement of the angular power spectrum of the Sunyaev-Zel'dovich (SZ) effect offers a simple way to determine dark-halo abundance at high redshift. In contrast to a conventional number-count analysis of halo abundance, the SZ angular power spectrum is insensitive to observational selection effects, e.g., flux, surface brightness, or volume limit of the survey. The SZ angular power spectrum is also insensitive to poorly known gas physics in the central region of gas in halos, as it is determined by the outer part of gas-pressure profile rather than the inner part. Theoretical understanding to the SZ angular power spectrum is, however, still in the early stage of its development. In this work, we attempt to make a refined analytic prediction for the SZ angular power spectrum, compare it with hydrodynamic simulations, and argue that our prediction approximates the simulations well, and can be used to fit forthcoming data of the SZ angular power spectrum to extract cosmological information.
May 3, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Cosmic Inflation and the Arrow of Time Andreas Albrecht, University of California
Cosmic inflation claims to make the initial conditions of the standard big bang "generic". But Boltzmann taught us that the arrow of time arises from very non-generic ("low entropy") initial conditions. I discuss how to reconcile these perspectives. The resulting insights give an interesting way to understand and compare inflation and other ideas that purport to offer alternatives to inflation.
May 17, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Dark Matter, Antimatter, and Local Cosmic Rays Dietrich Muller, The University of Chicago
Several recent measurements have been made to search for high-energy antiparticles in the local space environment. Most of the detected antiparticles are produced by high-energy interactions in the interstellar medium, but there are ongoing searches for features that could be related to dark matter particle annihilations. Ambitious investigations are in progress or planned that could provide more definive results.
May 24, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Reflections on Inflation Bob Wald, The University of Chicago
Inflationary models are generally credited with explaining the large scale homogeneity, isotropy, and flatness of our universe as well as accounting for the origin of structure. We argue that the explanations provided by inflation for the homogeneity, isotropy, and flatness of our universe are not satisfactory, and that a proper explanation of these features will require a much deeper understanding of the initial state of our universe. On the other hand, inflationary models are spectacularly successful in providing an explanation of the deviations from homogeneity. The main aim of the talk is to point out that the fundamental mechanism responsible for providing deviations from homogeneity--namely, the evolutionary behavior of quantum modes with wavelength larger than the Hubble radius--will operate whether or not inflation itself occurs. The key difference is that if inflation did not occur, one must directly confront the issue of the initial state of modes whose wavelength was larger than the Hubble radius at the time at which they were "born," and one's predictions will depend on these assumptions. Under some simple hypotheses concerning the "birth time" and initial state of these modes--namely, that semiclassical physics can be applied at all times on spatial scales larger than the grand unification scale and that all modes are "born" in their ground state--it is shown that, e.g., non-inflationary fluid models in the extremely early universe would result in a similar density perturbation spectrum and amplitude as inflationary models, without any "fine tuning." Such models should give a larger contribution of tensor modes than inflationary models, since there is no "slow role" enhancement of the scalar modes.
June 12, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Relativistic Corrections to the Sunyaev-Zeldovich Effects for Clusters of Galaxies Naoki Itoh, Sophia University
High-temperature plasmas exist inside the clusters of galaxies. The temperature is generally 5-15 keV. These high temperature electrons interact with the 2.728 K cosmic microwave photons and distort the Planck spectrum.This is the well-known Sunyaev-Zeldovich effect. Since some of the clusters have temperature as high as 15 keV, it is extremely important to include the relativistic corrections in the Sunyaev-Zeldovich effect. This has been successfully carried out recently by our group as well as some other groups. In this talk I will discuss the importance of the relativistic corrections. In fact they will be extremely important for the forthcoming short-wavelength observations of the Sunyaev-Zeldovich effect.