January 16, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Radiative Feedback from Galaxy Formation: the fate of the first galaxies Massimo Ricotti, University of Colorado
The theory of galaxy formation predicts that the creation process is hierarchical: small objects form first, and large galaxies form later from mergers of smaller subunits. The first galaxies are believed to have formed 100 million years after the Big Bang, at redshift $z sim 30$. In these primordial galaxies, the first stars emitted light into a previously dark universe and should have influenced the subsequent evolution of the universe in a still uncertain way. I present recent theoretical results on the formation and the evolution of the first (Population III) galaxies and effects of their self-regulating radiating feedback on the efficiency of star formation and reionization of the Universe.
January 23, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Reionization and Metal Enrichment of the High-Redshift Intergalactic Medium by the First Stars Aparna Venkatesan, CASA University of Colorado
The epoch, formation sites and effects of the first stars in the universe are some of cosmology's most intriguing yet unresolved questions today. Observations of the most distant quasars and galaxies to date imply that hydrogen reionization of the intergalactic medium (IGM) has occurred by redshifts of about 6. Radiation from the first stars is increasingly believed to have had a significant, if not the dominant, role in reionization, because of the mounting data on the decrease in the space density of bright quasars beyond redshifts of about 3. Early generations of stars are expected to be metal-free in composition, and to have signficantly harder ionizing spectra and evolutionary properties relative to their finite-metallicity counterparts. Here, I will present ongoing theoretical work that evaluates the effects of the first stars on the hydrogen and helium reionization, as well as the metal enrichment, of the high-redshift IGM. I will also discuss whether these signatures consistently reflect the same population of stars.
January 30, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Bounding the mass of the graviton and other topics in Gravitational Wave Phenomenology Lee Samuel Finn, Penn State
February 6, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Dark matter in normal galaxies Anatoly Klypin, New Mexico State University
Standard cosmological models, while very successful on large scales, face mounting problems on small scales. The models, for example, predict hundreds of dark matter subhalos inside of our Galaxy. Inner parts of rotation curves of dwarfs are not compatible with the theory. Yet, even more dramatic problem may be lurking on larger scales of normal Milky-Way type galaxies. I will discuss the situation on the amount of the dark matter in normal galaxies on scales from 10 parsec to 100 kpc, focusing on such issues as mass modeling of the Milky Way and M31 galaxies, rotation and existence of bars, microlensing counts.
February 13, 2002 | 3:30 PM | RI 480 | Wednesday colloquium Puzzling Cosmic Rays at the Highest Energies Angela Olinto, University of Chicago
February 27, 2002 | 3:30 PM | RI 480 | Wednesday colloquium The Pervasive Influence of Massive Black Holes in the Centers of Galaxies Douglas Richstone, University of Michigan
March 6, 2002 | 3:30 PM | RI 480 | Wednesday colloquium The distribution of thermal pressures in the Neutral Interstellar Medium Ed Jenkins,
January 11, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar MAJORANA: a next generation double-beta decay project Harry Miley, DOE/Pacific Northwest National Laboratory
The neutrino mass interest generated by recent atmospheric and solar neutrino oscillation results has led to the idea of a next generation neutrino mass experiment. Double-beta decay can measure the effective neutrino mass, but only with the availability of large quantities of enriched material, new underground facilities, and new technologies for background rejection. The Majorana Project seeks to build such an experiment based on the 20+ years of double-beta decay experience, plus several technological advances including the introduction of commercially available segmented germanium detectors.
January 18, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Polarization of the Cosmic Fireball Philip Farese, University of California Santa Barbara
The Cosmic Microwave Background (CMB), believed to be the remnant radiation from the Big Bang, has recently provided a wealth of information about the properties of our Universe. After a (very) brief review of theory and past Cosmic Microwave Background research I will focus on the benefit, prospects, and status of observing the polarization of the CMB. In particular I will discuss the design, observations, and data analysis of CoMPaSS (Cosmic Microwave Polarization at Small Scales), our recent polarization experiment.
January 25, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar p-brane factories Marco Cavaglia, MIT
The fundamental Planck scale may be of the order TeV in models of extra dimensions. If this is the case, particle collisions with center-of-mass energy larger than a few TeV and sufficiently small impact parameter are expected to generate black holes. For instance, high energy cosmic rays may produce black holes in the Earth's atmosphere. Production of spherically symmetric black holes has been discussed in recent literature. However, in presence of extra dimensions, one should also expect the creation of higher-dimensional objects (p-branes). In this talk we compute the cross section for p-brane creation. In spacetimes with asymmetric compactifications, we find that the cross section for the formation of a brane completely wrapped on small extra dimensions is higher than the cross section for the creation of black holes. Therefore, we predict that branes are more likely to be created in super-Planckian scattering processes than black holes. Future hadron colliders and cosmic rays detectors may be able to detect formation of these branes.
February 1, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Galaxies and Mass: SDSS Measurements on Halo Scales Tim McKay, University of Michigan
The luminous galaxies we observe are embedded in an extensive dark matter environment. Uncertainty in how our luminous tracers relate to the dark matter limits our understanding of large scale structure and galaxy formation. In this talk we describe SDSS weak lensing and dynamical measurements relating the luminous properties of galaxies to the dark matter environments in which they form. We also touch on the growing interplay between galaxy measurements and structure formation simulations, showing a example parallel analysis conducted on real and simulated universes.
February 8, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar First results from the Auger Engineering Array in Argentina Xavier Bertou, University of Paris VI
Xavier Bertou will speak about the first results from the large scale Auger prototype in Argentina.
February 15, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Light from Galactic Dark Matter P. Blasi, Osservatorio Astrofisico di Arcetri
The hierarchical clustering observed in cold dark matter simulations result in highly clumped galactic halos. If the dark matter in our Halo is made of weakly interacting massive particles (WIMPs), their annihilation products should be detectable in the higher density and nearby clumps. We consider WIMPs to be neutralinos and calculate the radiation from their annihilation products. In particular we concentrate upon the synchrotron emission of electrons and positrons in the galactic magnetic field and the gamma ray emission from the decay of neutral pions. Several new and promising avenues for the dark matter detection will be discussed.
February 22, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar "Standard Model Parameters, Black Holes, and Cosmology James Bjorken, SLAC
BJ is a very well known particle theorist who is turning his thoughts to Cosmology. He happens to be in town for personal reasons. Given our cancellation, he has kindly agreed to share some of his more speculative thoughts with us at our lunch. It should be fun for all.
March 1, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Making Dark Matter and Deriving Constraints with Neutrino Mixing in the Early Universe Kev Abazajian, Fermilab
Starting with a general description of mixed neutrinos in the early universe, one can explore different regimes of their behavior. In one, small active neutrino mixing with singlet neutrinos can overproduce primordial helium, distort the CMB, overproduce a diffuse photon background, or supply the dark matter. Decay photons from such a dark matter candidate may be detected with modern X-ray telescopes. In another regime, active-active neutrino mixing can constrain cosmological neutrino degeneracies (lepton numbers) given the large mixing angle solution to the solar neutrino problem and the primordial helium abundance.
March 8, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar Precision Studies with Galaxy Clusters? Gus Evrard, University of Michigan
Clusters of galaxies provide a critical interface between cosmological models of large-scale structure formation and the astrophysics of galaxy formation. Rich data streams emerging from large observational surveys offer the opportunity to impose detailed constraints on cosmology and astrophysics, but realizing this potential requires the ability to accurately compute expectations for cluster observables. This talk will review the current state of affairs in computational modeling of clusters, emphasizing which pieces of the problem appear to be solved to high precision (few per cent level) and which pieces need more attention. Uncertainty in the absolute mass scale of clusters remains the fundamental impediment to precise constraints on cosmology from cluster observations.
March 15, 2002 | 12:00 PM | LASR Conference Room | Friday noon seminar The Energy Spectrum and Mass Composition of Cosmic Rays at High Energy Alan Watson, University of Leeds
The derivation of the energy spectrum and mass composition of cosmic rays above 10**17 eV presents a considerable challenge. As well as necessitating accurate measurements of the cascades that the cosmic rays produce in the atmosphere, one must use models of particle physics processes in an energy range well above that explored by terrestrial accelerators to draw inferences. I will discuss recentwork done to improve our understanding of these issues and argue that, while there remains much to do, we are making substantial progress.