What is the Cosmological Significance of a Discovery of Dark Matter Particles?
Jacob Bourjaily (University of Michigan)
November 23, 2004
There are many reasons to suspect that our universe contains a large amount of cold dark matter. The most popular particle candidates for dark matter are weakly interacting massive particles (wimps). These particles are being searched for directly and indirectly by dozens of experimental groups throughout the world. Let us suppose that wimps are unambiguously detected in one or more of these experiments. Such a discovery would be an undeniable triumph of particle cosmology. Would it imply that we have solved the dark matter problem? Unfortunately, there is no reason to expect that dark matter is composed of a single type of particle. Furthermore, it is easy to provide examples of dark matter models (e.g. in supersymmetry) where nearly identical detector signals correspond to extremely different relic densities. Therefore, the density of wimps must be determined before their cosmological relevance is established.I will present ways to differentiate between many of the candidate dark matter particles. I will offer a general method to estimate (or determine) the density of the Lightest Supersymmetric Particle (LSP) within the most general minimally supersymmetric standard model.
The Gravitational Wave Universe
Bernard Schutz (Max Planck Institute for Gravitational Physics)
November 9, 2004
The LIGO gravitational wave project and its international partners will soon enter a phase of full-time observing. In a few years an upgrade will improve LIGO detectors' sensitivity by a factor of 10. Soon afterwards, the joint ESA-NASA space detector LISA will embark on a 10-year search for giant black holes, becoming the first detector to be limited by source confusion rather than detector noise. Already something like a thousand scientists spend some or all of their time developing these projects. What have they accomplished so far? What is left to do? What can we expect to learn with these instruments? What potential do they have to reveal aspects of the Universe that we know nothing about at present? I will address these and related questions using the most recently published detector data and theoretical studies of gravitational wave sources.
Unveiling the Universe
Joseph Silk (Oxford)
May 25, 2004
I will review the current situation with regard to dark matter, both baryonic and non-baryonic. I will discuss the implications for galaxy formation and the possibilities for detection of dark matter.
Event Horizons and the Generalized Second Law of Thermodynamics
April 20, 2004
The association of entropy with black hole event horizons by Bekenstein and Hawking hinted at deep linkages between quantum field theory, gravitation and information. Attempts have been made to sharpen this linkage through concepts such as gravitational entropy and the holographic paradigm. In this lecture I will present some new results that seek to clarify the relationship between black hole and cosmological horizon entropy, and extend the boundaries of the generalized second law of thermodynamics.
CORE: Frustrated Magnets, Charge Fractionalization and QCD
Marvin Weinstein (SLAC)
March 16, 2004
I will briefly explain the COntractor REnormalization group method (CORE) and show how it can be used to study various condensed matter systems. I then show how the same method can be used to map systems of massless free bosons, massless free and fermions interacting through gauge fields, into a class of generalized, highly frustrated anti-ferromagnets. I finally discuss the relation of these results to the lattice Schwinger model and QCD.
Exploring Young Brown Dwarfs
Ray Jayawardhana (University of Michigan Astronomy Department)
February 3, 2004
Brown dwarfs, which straddle the mass range between stars and planets, appear to be common both in the field and in star-forming regions. Their ubiquity makes the question of their origin an important one, both for our understanding of brown dwarfs themselves as well as for theories on the formation of stars and planets. I will present new results from a multi-faceted observational program that provide valuable clues to the formation and early evolution of sub-stellar objects. In particular, based on measurements of disk frequency in the infrared and accretion signatures in the optical, I will discuss whether young brown dwarfs undergo a T Tauri-like phase and if so how long that phase lasts. I will also show that surface gravities and effective temperatures of very low mass objects can be well determined from a multi-feature analysis of high-resolution spectra in comparison with the latest synthetic spectra. Combined with photometry and distance information, this allows us to derive the first mass and radius estimates for young substellar objects that are independent of theoretical evolutionary tracks. Our results are in good agreement with the track predictions, except for the coolest, lowest-mass objects, which appear both larger and less massive than the tracks predict. I will discuss the implications of these results.
Puzzle of Charge and Mass
Stuart Raby (Ohio State University)
January 19, 2004
Beginning with the seminal work of Rutherford, Geiger and Marsden in 1911, physicists have investigated the atom using particle beams (alpha particles, and protons) as probes. They developed new detection methods; the geiger counter, scintillators, cloud and then bubble chambers. This new paradigm for probing matter and new detectors lead to many discoveries. It is these principles and their logical extension which I will attempt to describe in this talk. It is these principles and their logical extension which I will attempt to describe in this talk