31 March 2006	28 April 2006	2 June 2006
7 April 2006	5 May 2006	9 June 2006
14 April 2006	19 May 2006
21 April 2006	26 May 2006

Jeremy Tinker, University of Chicago

Modeling Galaxy Clustering with the Halo Occupation Distribution  

Measurements of the galaxy two-point correlation function create strong constraints on the statistical occupation of galaxies within dark matter halos, referred to as the Halo Occupation Distribution (HOD). Using the HOD, one can make predictions for other clustering statistics for a given cosmology. Recent results have demonstrated a tension between galaxy clustering results and the so-called "concordance cosmology". These results include cluster mass-to-light ratios, galaxy pairwise velocity dispersions, and redshift-space anisotropies. All of these discrepancies are ameliorated if one assumes a cosmology in agreement with the new WMAP year 3 results. This methodology for constraining the HOD relies on the simplifying assumption that halo occupation is a function of halo mass only, independent of the halo's environment. This assumption has been called into question with recent theoretical results. I will present new measurements of void statistics from the SDSS public DR4 database and compare these data to HOD predictions using the standard assumptions. Voids provide a sensitive test for the environmental dependence of halo occupation, a test the HOD passes with flying colors.

Michael Boylan-Kolchin, UC, Berkeley

Major mergers and the assembly of massive elliptical galaxies  

Several independent lines of evidence indicate that gas-poor mergers play an important role in assembling massive elliptical galaxies. Since low-redshift ellipticals are observed to obey well-defined scaling relations, dissipationless mergers can place interesting constraints on galaxy formation theories. I will present the results of numerical simulations of these mergers, including their locations relative to the observed fundamental plane, Faber-Jackson, and stellar mass-size relations, as well as possible implications for the black hole M-sigma relation in massive galaxies. I will also discuss dissipationless merging in the context of the formation of giant ellipticals and brightest cluster galaxies.

Mark Neyrinck, University of Hawaii

The Cosmological Information Content of the Halo-Model Dark-Matter Power  

I will discuss explorations, using the halo model, of the information content as a function of scale of the nonlinear dark-matter power spectrum. The halo model gives similar results as Rimes and Hamilton recently found from N-body simulations. Both methods predict a paucity of cosmological information on translinear (k ~ 0.1-1 h/Mpc) scales, which may be partially explained in the halo model by Poisson fluctuations (particularly large for the largest haloes) in halo number density in a given volume. I will also discuss whether information is preserved in time in the halo model, and how halo model parameters might be constrained by requiring that information cannot be created.

Dan Kapner, KICP

Tests of Newton's Inverse Square Law to Short Distances  

I will describe a series of experiments that test the Inverse-Square Law (ISL) down to 65 micron separations. A variety of physics beyond the standard model motivates such a search; the exchange of new bosons, extra dimensions, or even the energy scale of dark energy might lead to a violation of the ISL. Our torsion balance tests set new limits for these scenarios. New results will be presented.

Joel Primack, University of California, Santa Cruz

Galaxy Mergers: Simulations, Observations, and Active Galactic Nuclei  

In this informal talk, I will summarize the large suites of high-resolution hydrodynamic simulations of galaxy encounters that my current and former PhD students have been running and analyzing, and comparisons with observational data especially from the ongoing DEEP2 survey. In particular, I will discuss what the data from DEEP tell us about the morphologies of the galaxies that host AGNs, and the interesting implications for theoretical models. The people involved include my former PhD students T.J. Cox and Patrik Jonsson (who stayed on at UCSC as a postdoc), my current students Greg Novak, Matt Covington, and Christy Pierce, and my former postdoc Jennifer Lotz.

Mark Chen, Queen's University

Neutrino Physics Beyond SNO  

The Sudbury Neutrino Observatory (SNO) will stop taking data at the end of 2006. The heavy water in SNO will be removed in 2007. What should be done next? By filling SNO with a liquid scintillator (called SNO+) a new, multipurpose detector with diverse physics goals could be a successor. Located in the deepest underground lab, SNO+ would have unique capabilities including detection of pep and CNO solar neutrino. By measuring the flux of pep solar neutrinos, with precision, one can test the neutrino-matter interaction which is sensitive to new physics. SNO+ could also detect geo-neutrinos -- the neutrinos from radioactivity in the Earth -- and is favourably located for such a measurement since it is surrounded by Canadian Shield continental crust, a simple geological configuration. Fundamental questions in geoscience could be addressed by a SNO+ geo-neutrino measurement. Lastly, double beta decay isotopes might be deployed in the liquid scintillator resulting in a competitive next-generation search. The prospects are being studied and SNO+ R&D will be presented.

Olivier Dore, CITA

Mapping the Polarized Sky with WMAP: Methods and Cosmological Implications  

The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite designed to produce high resolution full sky maps of the temperature and polarization of the cosmic microwave background (CMB). The accurate characterization of the fluctuations in the CMB contains exquisite information about the global structure, composition, and evolution of the universe. Relying on the first three years of observations, WMAP has now measured these fluctuations with unprecedented accuracy. I will illustrate how a greater signal-to-noise in the temperature measurement but also a new large scale polarization signal detection have significantly sharpened our cosmological interpretation. A simple six-parameters cosmological model (flat LCDM); consisting of baryons, dark matter, a cosmological constant, initial perturbation spectrum amplitude and slope, and optical depth; is an excellent fit to the WMAP data, as well as a host of other astronomical experiments. The new WMAP data also hint at a small deviation from scale invariance in the primordial fluctuation power spectrum, a key prediction of inflation. If confirmed this would strengthen our confidence in the inflationary scenario and allow detailed model testing. Besides, the combination of WMAP data and other astronomical data places even stronger constraints on the density of dark matter and dark energy, the properties of neutrinos, the properties of dark energy and the geometry of the Universe.

Lisa Kewley, University of Hawaii

The Star Formation and Metallicity History of Disk Galaxies: 0  

Observing the star formation rate and chemical abundances since the earliest times in the universe is crucial to understanding galaxy formation and evolution. I present results from (1) our investigation into the H-alpha, infrared, and [OII] star formation rate (SFR) indicators and (2) our recent investigation into the metallicity history of galaxies between redshifts 0

Elizabeth Hays, The University of Chicago and Argonne National Laboratory

High Resolution Imaging of Cerenkov Light from Air Showers  

Above TeV energies, the cosmic-ray flux becomes prohibitively small for direct observations by balloon-borne detectors. However, large ground-based arrays cannot be used to identity the type of nucleus initiating an air shower on an event-by-event basis and so, the inferences of cosmic-ray composition depend heavily on simulations and have large uncertainties. The Cerenkov emission accompanying an air shower includes light from the primary nucleus passing through the upper atmosphere before the first interaction. This "direct" Cerenkov component is a very fast and compact signal that provides a measurement of the charge of the primary particle using an air Cerenkov telescope with sufficiently high angular and timing resolution. In addition to a precision measurement of composition at TeV energies, the ability to identify the type of particle generating an air shower has potential applications to ground-based gamma-ray observations, where cosmic-rays are a dominant background. The Track Imaging Cerenkov Experiment, TrICE, is a prototype instrument to test the use of a high resolution camera in a Cerenkov telescope and to look for the "direct" Cerenkov component of cosmic-ray-induced air showers. TrICE has been constructed at Argonne National Lab and is currently being commissioned. I will discuss the "direct" Cerenkov measurement and show some of the first data taken with TrICE this Spring.

Niayesh Afshordi, Harvard University

Digging for new (Astro-)Physics in the old CMB  

The residents of KICP need little reminder that there is much more to CMB than the last scattering surface. The secondary anisotropies, even though a foreground to the high redshift universe, illuminate the nature of different astrophysical processes, and may even open a window to new physics on large scales. I start by summarizing different attempts to detect the Integrated Sachs-Wolfe (ISW) effect, and the constraints that they put on theories of dark energy, or modified gravity, including a theory which may only be distinguished from LCDM through its ISW signature. Turning focus onto small scales, I outline an optimized method to extract the SZ signature of the intracluster medium (ICM) from a low resolution CMB map (such as WMAP), in combination with an X-ray cluster catalog. I then report an 11sigma, model-independent detection of the SZ signal in the WMAP 3yr, and the resulting ICM pressure profile around the virial radius.

29 March 2006	26 April 2006	17 May 2006
5 April 2006	3 May 2006	24 May 2006
12 April 2006	10 May 2006

Re'em Sari, Caltech

The Formation of the Solar System  

How do planets form and how long does it take? Why are their orbits circular and coplanar? What set the number of planets in our solar system? We address these fundamental questions providing a coherent story on the formation of our solar system.

Bhuvnesh Jain, University of Pennsylvania

Gravitational Lensing with Large Imaging Surveys  

I will describe the ideas and challenges in using gravitational lensing for cosmology. Recent results in weak lensing and the observational challenges ahead will be discussed. With planned multi-color imaging surveys, weak lensing can probe dark energy and constrain alternate theories of gravity. I will compare the strengths and weaknesses of lensing with other observational methods.

Sara Seager, Carnegie Institute of Washington

Extrasolar Planets: From Hot Jupiters to Hot Earths and Beyond  

We have entered a new era in planetary astrophysics with over 170 extrasolar giant planets now known. Physical properties of a subset of these planets---the hot transiting giant planets---have been measured, including mass, radius and thermal emission. Even more intriguing than the hot Jupiters are the seven known hot super-massive Earths (mass range 7 to 20 Earth masses), which are expected to consist of a large rocky component. There is a chance to observationally study this class of planets in the near future. Beyond the hot Earths, our own Earth has been studied as an exoplanet, both in its present state and in its paleoclimates. I will summarize which exoplanet physical characteristics can be inferred from spectra, the interpretation of the hot Jupiter spectral data, the possibilities for observation and interpretation of hot supermassive Earths, and the scientific highlights and prospects for the future detection and study of and planets like Earth.

Feryal Ozel, University of Arizona

Peeking into a Neutron Star: Neutrons, Condensates, or Quarks?  

Neutron stars are the densest objects in the universe and may contain hyperon-dominated matter, condensed mesons, or even deconfined or strange quark matter. Because of their low temperatures and high chemical potentials, the physical conditions in their interiors differ greatly from the dense conditions of the early universe or those achieved at hadron colliders. This region of the QCD phase diagram can only be probed through astrophysical observations that measure the mass and radius of neutron stars. For decades, this effort has been hampered by a number of model uncertainties as well as by the lack of accurate measurements of different spectroscopic phenomena from a single source that would break the degeneracies between the neutron star parameters of interest. I discuss how we can now overcome these problems by combining recent developments in our understanding of neutron star atmospheres with observations of distinct phenomena from the same neutron star source. In particular, I report the first unique measurement of the mass and radius of the neutron star source EXO 0748-676. The high inferred mass and large radius of this neutron star rule out all the soft equations of state of neutron star matter. This result shows that condensates and unconfined quarks do not appear under the conditions found in the centers of the neutron stars.

Heather Morrison, Case Western Reserve University

Forming the Milky Way Halo: smooth vs chunky  

I will summarize our current understanding of the formation of the Galaxy's halo, using a number of different samples of halo stars from surveys including SDSS-II's SEGUE. Evidence is mounting for a "chunky" origin for much of the halo, via infall of satellite galaxies and subsequent formation of star streams. I will also discuss constraints on the smooth halo from a new, high-quality sample of metal-poor stars in the solar neighborhood.

Andy Albrecht, University of California, Davis

Report from the Dark Energy Task Force  

Understanding the observed cosmic acceleration is widely ranked among the very most compelling of all outstanding problems in physical science. Many believe that nothing short of a revolution will be required in order to integrate the cosmic acceleration (often attributed to “dark energy”) with our understanding of fundamental physics. The DETF was formed at the request of DOE, NASA and NSF as a joint subcommittee of the Astronomy and Astrophysics Advisory Committee (AAAC) and the High Energy Physics Advisory Panel (HEPAP) to give advice on optimizing our program of dark energy studies. To this end we have assessed a wide variety of possible techniques and strategies, and developed a series of factual findings and recommendations. I will present our main conclusions and discuss their implications.

Craig Hogan, University of Washington

Gravitational Waves from Strings  

Long discredited as the main source of cosmological perturbations, cosmic strings have re-emerged as natural structures in string theory and natural products of stringy inflation. Techniques will be discussed for detecting them, or setting limits on parameters such as the mass per unit length, using gravitational wave backgrounds. The most sensitive current probe is millisecond pulsar timing; in the future, it will be LISA.

Wendy Freedman, Carnegie Institute

The Giant Magellan Telescope  

The Giant Magellan Telescope (GMT) is a 21-5-meter collecting-area optical/near-infrared telescope with a resolution of a 24.5-meter. The baseline site for the GMT is Las Campanas, Chile. The GMT primary mirror is comprised of seven borosilicate 8.4-meter segments, and the secondary contains seven fast-steering segments aligned to each of the primary mirrors. The first of the primary mirrors has been cast at the Steward Observatory Mirror Laboratory, and preparations are underway for its polishing and testing. Several instrument concepts have been developed covering the wavelength range from the UV/optical to the thermal infrared. The project has just undergone a Conceptual Design Review, with a recommendation to proceed to the Design Development Phase. The Science Working Group has identified several areas where the GMT will have an impact. These include: 1) the nature of dark matter and dark energy 2) the first stars and galaxies 3) star and planet formation 4) the evolution of galaxies and 5) the growth of black holes. Unique capabilities of the GMT include wide-field (~10-arcminute FOV) spectroscopy and the direct detection of exoplanets. The GMT is a consortium of research institutions consisting of the Australian National University, the Carnegie Institution of Washington, Harvard University, Massachusetts Institute of Technology, Texas A&M University, Smithsonian Astrophysical Observatory, University of Arizona, University of Michigan, and the University of Texas at Austin.

19 April 2006

Mikhail Medvedev, University of Kansas

Do Extragalactic Cosmic Rays Induce Cycles in Fossil Diversity  

Recent work has revealed a highly statistically significant 62 +/- 3-million-year cycle in the number of marine genera. This implies a periodic process extending back 540 My. While astro- and geophysical phenomena may be periodic, no plausible mechanism has been found. The fact that the period of the diversity cycle is so close to the 64 My period of the vertical oscillation of the Solar system relative to the galactic disk is suggestive. We propose that the diversity cycle is caused by the anisotropy of cosmic ray (CR) production in the galactic halo/wind/termination shock and the shielding effect of the galactic magnetic fields. CRs affect the biosphere in a number of ways: they cause DNA damage, mutations and cancer due to increased radiation, affect the atmospheric ozone concentration and UV protection, initiate cloud formation, and can affect climate. The high statistical significance of (i) the phase agreement between maximum excursions of the Sun toward galactic north and minima of the diversity cycle and (ii) the correlation of the magnitude of diversity drops with cosmic ray peak values through all cycles provide solid support for our model.

6 April 2006

18 May 2006

22 May 2006

Stephan Meyer, University of Chicago

Three Year WMAP Results  

Three years of Wilkinson Microwave Anisotropy Probe (WMAP) data have now been analyzed. The 3 year data analysis is improved over that of the first-year WMAP publications by better models of the instrument characteristics, improved map making and a complete polarization analysis. The 3-year full-sky maps of intensity and polarization in 5 microwave bands are used to test cosmological and galactic foreground models. With the higher sensitivity and polarization information, a Lambda Cold Dark Matter (LCDM) model remains an excellent fit to the data with parameters consistent with the first-year publications. The polarization maps have improved the determination of the optical depth of scattering due to reionization and reduced the degeneracy with other parameters, particularly the primordial spectral index of fluctuations. When the new WMAP data are combined with those of small angular-scale CMB experiments, an independent measure of the Hubble constant and large-scale structure and supernova results, improved constraints on the dark energy equation of state, the total curvature, and the sum of the neutrino masses are obtained.

Cristiano Germani, DAMTP, University of Cambridge

Mirage Inflation  

A cosmological model based on an inhomogeneous D3-brane moving in an AdS_5 X S_5 bulk is introduced. Although there is no special points in the bulk, the brane Universe has a center and is isotropic around it. The model has an accelerating expansion and its effective cosmological constant is inversely proportional to the distance from the center, giving a possible geometrical origin for the smallness of a present-day cosmological constant. Besides, if our model is considered as an alternative of early time acceleration, it is shown that the early stage accelerating phase ends in a dust dominated FRW homogeneous Universe. Mirage-driven acceleration thus provides a dark matter component for the brane Universe final state. We finally show that the model fulfills the current constraints on inhomogeneities.

Walter Ogburn, Stanford

Position reconstruction analysis for CDMS-II  

The CDMS-II dark matter direct detection experiment uses ZIP detectors, which provide rich information about every event. The four phonon sensors and two ionization sensors allow discrimination of nuclear recoils (such as WIMPs) from electron recoils (such as most backgrounds), and also allow rejection of near-surface events using phonon timing and pulse shape. The method of expectation-maximization is being applied to develop an empirical detector model that accounts for the dependence of detector observables on event location, recoil type, and energy. This model has been used to very effectively reconstruct the physical location of particle interactions within a ZIP detector. It provides a natural way to extract information from observables that are often badly behaved, and will be used as a framework extracting as much information as possible from the ZIP detector in rejecting backgrounds to achieve the best possible sensitivity to WIMP recoils.