April 2, 2003 | 3:30 PM | RI 480 | Wednesday colloquium Frontiers in Neutrino Astrophysics John Beacom, Fermilab
There has been great progress in neutrino physics recently, with the solar and atmospheric neutrino problems finally solved. Now what? I will argue that this is not the beginning of the end in neutrino physics, but only the end of the beginning. Knowledge of the neutrino mixing parameters makes neutrinos a unique and reliable probe of astrophysical objects and cosmology. It also allows much more sensitive tests of exotic neutrino properties that would indicate truly new physics. I will discuss the present picture of neutrino physics and some of the key steps to complete it, and then the promising future for opening new windows on the universe and the mysterious neutrino sector.
April 16, 2003 | 3:30 PM | RI 480 | Wednesday colloquium Might Lorentz symmetry be violated? Ted Jacobson, University of Maryland
Quantum gravity considerations suggest that Lorentz symmetry may hold only approximately. This talk will discuss a phenomenological framework for incorporating Lorentz violation into particle physics and general relativity, some of the possible consequences, and the observational constraints. High energy astrophysics observations impose such strong constraints as to render Lorentz violation at order E/E_Planck highly unlikely.
April 30, 2003 | 3:30 PM | RI 480 | Wednesday colloquium Neutrino Mixing, Oscillations and Neutrinoless Double-Decay:Majorna and Cuore Next Generation Experiments Frank Avignone, USC
Analyses of the latest solar neutrino oscillation data from both Super-Kamiokande and from SNO have significantly changed the structure of the neutrino-mising matrix. The very recent reported results from the KAMLAND experiment strongly support the Large Mixing Angle (LMA) solution to the solar neutrino problem. The new values of the mixing angles differ significantly from those that favored the bi-maximal mixing scenario. The new experimental values strongly suggest that the probability that planned next generation double-beta decay experiments have a significant probability of being able to discover this exotic decay mode and measure the effective Majorana mass of the electron-neutrino. This is the only pratical method of determining that neutrinos are Majorana particles. The measurement of the effective mass would determine the mass scale of the three families of neutrinos in the three family scenario. The phenomenology of neutrino-mixing, neutrino oscillations, and the connection to the neutrinoless double beta decay will be reviewed. A propsed next generation experiments, MAJORANA, and CUORE will be described in some detail and their projected sensitivities and discovery potential be discussed. Neutrino oscillation experiments have clearly demonstrated that neutrinos have mass and they have established the minimum mass of the heaviest neutrino, but even in principle they can not determine the mass scale but only the differences between the squares of the neutrino mass-eigenvalues. Neutrinoless double beta decay is the next important step in gaining a more complete understanding of neutrino physi. Their time has come. The status of the MAJORANA proposal and the CUORICINO experiment will also be discussed.
May 14, 2003 | 3:30 PM | RI 480 | Wednesday colloquium Supermassive Black Holes in Galactic nuclei Monica Valluri, University of Chicago
There is now irrefutable dynamical evidence for Supermassive Balckholes at the centers of several nearby galaxies and complelling evidence that compact mass concentrations-probably black holes exist in the nuclei of an handful of galaxiees with elliptical/bulge components. One of the most important developments in the study of the demographics of galactic nuclei was the simultaneous discovery (by two different groups) of a tight empirical correlation between the masses of SBHs and the velocities of stars in their host bulges. There has been considerable controversy regarding the precise parameters of this correlation, and this has spawned a plethora of theoretical models for the formation of supermassive black holes. Many of the SBHs contributing to this correlation have had their masses estimated from three-integral, axisymmetric, orbit-based modeling algorthms which aim to recover the parameters defining the gravitational potential in spheroidal stellar systems using stellar kinematical data from the Hubble Space Telescope's STIS Spectograph and other spectographs. I will review the demographic realtionships between supermassive black holes and their host galaxies and critically evaluate the ability of the most popular modelling algorithms to recover the masses of central blackholes. I will show that the black hole mass estimation problem is generically under-determined: a range of parameters can provide equally good fits to the data, making it impossible to assign best-fit values. I will show that the range of degeneracy in black hole mass depends strongly on the degree to which the data resolve the radius of influence of the black hole, implying that the modelling errors on existing black hole mass estimates have so far been significantly underestimated.
April 4, 2003 | 12:00 PM | LASR Conference Room | Friday noon seminar Synchroton Radiation at Radio Frequencies from Cosmic Ray Air Showers Denis Suprun, U of C
I will review some of the properties of extensive cosmic ray air showers and describe a simple model of the radio-frequency radiation generated by shower electrons and positions as they bend in the Earth's magnetic field. Simulation involves calculating the trajectory and radiation of a few thousand charged shower particles. The results are then transformed to predict the strength and polarization of the electromagnetic radiation emitted by the whole shower.
April 11, 2003 | 12:00 PM | LASR Conference Room | Friday noon seminar Causal sets as the deep structure of spacetime Fay Dowker, Queen Mary, University of London
One approach to solving the problem of quantum gravity is based on the causal set hypotheis, which states that the deep, quantum structure of spacetime is discrete and is what is known in mathematics as a "partial order" or "poset", a kind of extended family tree. Causal set theory has now reached a stage at which questions of phenomenology are beginning to be addressed. this talk will introduce the basic concepts and motivations behind the hypothesis and address some of the latest developments which include: (i) an apparently confirmed order of magnitude prediction for the cosmological constant, the only prediction made in any propsed theory of quantum gravity that has been subsequently verified by observation (ii) a classical stochastic causal set dynamics which arguably is the most general consistent with the discrete analogs of general covariance and classical casuality (iii)the formulation of a "cosmic renormalization group" which indicates how one might in principle solve some of the "large number puzzles" of cosmology without recourse to post-quantum-era inflation (iv)a rigorous characterization of the observables(or "physical quetions")of causal set cosmology,at least in the classical case.
April 18, 2003 | 12:00 PM | LASR Conference Room | Friday noon seminar Gravitational Leakage Into Extra Dimensions: How the Sun Can Shed Light on Dark Energy Arthur Lue, Case Western
Theories suggesting that the universe may indeed contain dimensions beyond the three that we observe have recently captured the imagination of physicists and the public alike. The braneworld model of Dvali-Gabadadze-Porrati poses that we are oblivious to these extra dimensions because gravity leaks excruciatingly slowly off our three-dimensional universe. Cosmology in this model has been shown to support both "conventional" and exotic explanations of the dark energy responsible for today's cosmic acceleration . I present new results suggesting how, in this theory, local measurements of gravity(e.g., within the solar system) can be sensitive to that cosmology, and point out how imminent improvements in solar system ranging experiments and future satellite missions at the end of the decade are poised to observe, or rule out, the discussed effects.
May 9, 2003 | 12:00 PM | LASR Conference Room | Friday noon seminar Gravitational Lens Ensembles as a Probe of Galaxy Structure and Evolution David Rusin, Harvard-Smithsonian Center for Astrophysics
Gravitational lenses represent a unique sample of galaxies. they are mass-selected, dominated by early-type morphologies, and naturally span the redshift range 0< z< 1. Moreover, the observed properites of lensed images are sensitive to the galaxy mass distribution, and the geometry provides a model-independent measurement of the projected mass. Lenses are thus powerful tools for investigating the structure and evolution of ealry-type galaxies. I will review recent progress on these fronts using individual lenses, and introduce statistical methods to constrain the radial mass profile in early-type galaxies, trace the eveolution of their stellar populations, and address the relationship between luminous and dark matter on galaxy scales.
May 16, 2003 | 12:00 PM | RI 480 | Friday noon seminar Constraints on Superheavy Dark Matter Ivone Albuquerque, University of California Berkeley
The dark matter in the universe might be composed of superheavy particles(mass >~10^10 GeV). These particles can be detected via nuclear recoils produced in elastic scatterings from nuclei. We estimate the observable rate of strongly interacting supermassive particles(simpzillas) in direct matter search experiments. The simpzilla energy loss in the Earth and in the experimental shields is taken into account. The most natural scenarios for simpzillas are ruled out based on recent EDELWEISS and CDMs results. The dark matter can be composed of superheavy particles only if these interact weakly with normal matter or if their mass is above 10^15 GeV. A comparison with simpzilla indirect detection will also be made.
May 30, 2003 | 12:00 PM | LASR Conference Room | Friday noon seminar The elusive binary black hole coalescence Deidre Shoemaker, Cornell University
For over a decade, one of the major goals in the field of numerical relativity has been simulating the coalescence of two blak holes, a key source for gravitaional wave observatories. This has turned out to be an elusive task despite many successes over the last few years. I will present the current status of binary black hole collisions and address what the future brings.
June 6, 2003 | 12:00 PM | LASR Conference Room | Friday noon seminar Galaxy Clustering in the SDSS Redshift Survey Idit Zehavi, University of Chicago/CfCP
I will present recent measurements of galaxy clustering in the Sloan Digital Sky Survey redshift survey. The current sample consists of 170,000 galaxies up to a redshift of 0.2, covering about 2500 square degrees. We measure the clustering in redshift space and in real space. The two-dimensional correlation function shows clear signatures of redshift distortions. The inferred real-space correlation function can be generally described by a power law. However, we detect subtle but systematic departures from a power law. These departures can be naturally explained by contemporary models of galaxy clustering. The SDSS is especially suitable for investigating the dependence of clustering on galaxy properties, and I will focus on the dependence of clustering on color and on luminosity.
May 8, 2003 | 12:00 PM | LASR Conference Room | Special seminar The Analysis and Interpretation of the Wilkinson Microwave Anisotropy Probe Data David Spergel, Princeton University
In this talk, I will describe the different approaches that the WMAP team used in the analysis of the microwave background temperature power spectrum. The talk will describe the methodology used for error propogation and for foreground modeling. I will also describe how we use the likelihood function to explore cosmological models.