Tokonatsu Yamamoto, CfCP

Recently, small scale anisotropy in the distribution of arrival direction of Ultra High Energy Cosmic Ray (UHECR)has been detected by AGASA. They reported clusters above 10^19 eV correlated with the Galactic magnetic field. This result is an indication that UHECRs come from extra-galactic point sources and are charged particle. Motivated by this observational result, we have simulated propagation of high energy nucleus in the extra-galactic photon and magnetic field. Based on the result of this simulation, energy distribution of the UHECR will be discussed.

Michael Santos, Caltech

The reionization of hydrogen represents not only a landmark achievement by early luminous sources, but also had a considerable effect on the subsequent formation of stars and galaxies: reionization inhibits star formation in some proto-galaxies, in a way that depends on their total mass and formation history. I will show results suggesting that reionization plays a crucial role in understanding globular cluster formation. I will also present observations of z=5 galaxies, where the Lyman-alpha line luminosity function provides a test of the effect of reionization on star formation in proto-galaxies.

Maximo Ave, CfCP

Efforts to understand the origin of cosmic rays at any energy are greatly hampered by our lack of knowledge of the mass distribution in the incoming cosmic ray beam. Even with the traditional ground arrays it has been possible to devise ways of deducing the primary energy that are reasonably independent of model and mass uncertainties, at least at the 30 % level. However use of the data on the energy spectrum and arrival direction distribution to decide between various origin models does require knowledge of the primary mass distribution. We try to review the experimental status of mass composition measurements of primary cosmic rays above 10¹⁹ eV.

Mark Hoffman

Models of dark energy are conveniently characterized by the equation-of-state parameter w=p/
ho, where
ho is the energy density and p is the pressure. Imposing the Dominant Energy Condition, which guarantees stability of the theory, implies that wgeq -1. Nevertheless, it is conceivable that a well-defined model could (perhaps temporarily) have w<-1 , and indeed such models have been proposed. We study the stability of dynamical models exhibiting w<-1 by virtue of a negative kinetic term. Although naively unstable, we explore the possibility that these models might be phenomenologically viable if thought of as effective field theories valid only up to a certain momentum cutoff. Under our most optimistic assumptions, we argue that the instability time scale can be more than the age of the universe, but only if the cutoff is at or below 100 MeV. We conclude that it is difficult, although not necessarily impossible, to construct viable models of dark energy with w<-1 observers should keep an open mind, but the burden is on theorists to demonstrate that any proposed new models are not ruled out by rapid vacuum decay.

Thushara Perera, CfCP

Due to a variety of advantages they offer, Transiton Edge Sensors,(TESs)are slated for use in many upcoming experiments in astrophysics. I will describe the principles of operation and biasing and readout scheme used with TESs which involves the use of SQUID magnetometers. I will also discuss why they are desirable for use in bolometers and dark matter detectors. The desireable properties include superior speed, linear and stable response, low noise levels, and adaptability to a multiplexed readout scheme which facilitates their use in large-scale arrays.

Erin Scott Sheldon, CfCP

I will present a galaxy-galaxy lensing study based upon data from the Sloan Digital Sky Survey. Galaxy-galaxy lensing on intermediate to large scales(R>200kpc) is a direct measure of the galaxy -mass cross correlation function w_{gm}. By comparing w_{gm} bias between the galaxy distribution and the underlying mass distribution. This relatiopnship is of fundamental importance to the understanding of galaxy formation. Because lensing is a measure of the excess mass, these measurements can also be used to constrain the mass-to-light ratio of the large scale structure surrounding galaxies. By comparing to the galaxy-luminosity correlation function w_{gL}, we constrain the bias between luminosity and mass, and the radial dependence of the mass-to-light ratio around galaxiies.

Andrew Sonnenschein

The identification of the non-baryonic component of the dark matter is one of the most urgent problems in cosmology. This is a very exciting problem for experimentalists, because of the possibilities for greatly increased sensitivity that are being opened up by new detection technologies. Weakly interacting massive particles (WIMPs), especially the neutralinos predicted by supersymmetry, are a leading candidate to be the dark matter, and the search for these particles is now being intensely pursued by diverse methods, in experiments such as CDMs, DAMA, and ZEPPLIN. A particularly interesting detection technique for future experiments involves the use of bubble nucleation in superheated liquids to discriminate against backgrounds from environmental radioactivity. These experiments operate in a mode similar to bubble chambers, but under pressure conditions that reduce sensitivity to backgrounds. In principle, this approach can be used to construct very large detectors, which would improve sensitivity by orders of magnitude. I will discuss the initial attempts to use this effect in ongoing experiments, and a new variation on the technique which we are exploring at the Center for Cosmological Physics.

Alan Peel, University of California, Davis

Galaxy clusters are the next best thing for precision cosmology probes after the Cosmic Microwave Background. With the recent dramatic increase in sensitivity and resolution of sub-mm wavelength observations, we will soon begin to measure galaxy cluster peculiar velocities via the Sunyaev-Zel'dovich effect. However, detailed modeling of point sources, CMB comtamination and velocity/temperature substructure within the cluster itself is required to acquire useful measurements with sufficient precision for cosmology. I will discuss what cosmology can be accomplished with cluster velocities and seperately, how we an model observations to optimize velocity measurements. This is work in progress supported in part by a NASA Graduate Student Research fellowship.

Andreas Berlind, CfCP

The relation between the galaxy and mass distribution is uncertain because it depends on the complex and poorly understood process of galaxy formation. This "bias" between galaxies and mass has long been seen as an obstacle for studies of galaxy clustering tht attempt to constrain cosmological models. An alternative view, however, is that the existence of bias makes it possible to constrain galaxy formation theories by studying galaxy clustering. I will describe the "Halo Occupation Distribution", (HOD),a realtively new formulation of bias that is based on the distribution of galaxies in dark matter halos. I will illustrate the power of this approach and show how it can be used to measure the bias empirically and connect observations of galaxy clustering to the physics of galaxy formation. Finally, I will present constraints on the HOD from measurements of galaxy clustering in the Sloan Digital Sky Survey.

Daniel Holz, CfCP

Because we live in an inhomogeneous universe, all distant sources are gravitationally lensed. We derive these lensing effects, paying particular attention to the distribution of amplifications of distant standard candles. Lensing is found to be an important source of noise in attempts to measure the evolution of the universe with high-redshift supernovae. We discuss various ways to minimize this lensing noise. As the lensing results from the gravitation of intervening matter, a direct measurement of the lensing signal shed light on the distribution of dark matter in the universe. We conclude with a discussion of the impact of lensing on proposed next generation high- redshift supernova surveys.

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.

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.

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.

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.

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.

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.

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.

Nick Gnedin, University of Colorado

Cosmological reionization-the process of ionization of the bulk of cosmic gas by ultra violet radiation from primeval galaxies-is by far the most dramatic event that occurred in the universe since the formation of the first star. I will overview recent observational and theoretical progress(and regress)in our understanding of reionization, and will discuss the future observational avenues that are going to open for us in the next decade.

Pengjie Zhang, FNAL

The Sunyaev Zeldovich (SZ) effect directly probes the thermal and kinetic energy of ionized baryons and so is a sensitive measure of the thermal history of the universe. I will discuss the two key ingredients of its precision modeling: analytical models and hydrodynamic simulations. I will address various limitations in these two approaches and the way to quantify and overcome them. I will then forecast the power of planned SZ experiments to measure the thermal history of the universe.

Yong-Seon Song, University of California, Davis

Precision cosmological observations can determine a large number of cosmological parameters which are the keys to understanding the Universe. I sort out all parameters into three types:primordial parameters(primordial power spectrum amplitudes, scalar tilt, tensor tilt, etc.),intermediate parameters (which are mainly determined at last scattering surface) and low-redshift parameters(neutrino mass, dark energy,etc.). Future CMB experiments will allow us to determine the primordial parameters and intermediate parameters. With the primordial and intermediate parameters highly constrained, low-redshift observations can be used to place amazingly tight constraints on the low-redshift parameters. In particular I show how the dark energy component's equation-of-state parameter can be determined as a function of redshift with future observations such as LSST nd Planck or CMBpol.

Paul Sommers, University of Utah

Observations of cosmic rays above the expected GZK spectral cut off have challenged every model of their production and propagation. The Auger Observatory will provide copious high-quality data to disspell the mysteries and identify the sources of high energy cosmic rays. Its collecting power will exceed that of previous experiments by more than an order of magnitude. It will have full-sky coverage for sensitive anisotropy analyses. Exploiting the combination of surface detectors and air fluorescence detectors, it will accurately measure the energy and arrival detection of each cosmic ray, and it can statistically determine the types of primary particles. The observatory in Argentina is now operational and growing day by day.

Marcus Runyan, Unversity of Chicago

I will discuss the Arcminute Cosmology Bolometer Array (ACBAR) experiment which made observations of small-scale CMB anisotropy from the South Pole in 2001 and 2002. ACBAR is a multi-frequency millimeter-wave bolometer array with ~5' resolution from the 2m Viper telescope. I will describe the instrument and the results from the first two years of the project, as well as expectations from observations in 2004 and 2005.

Ariyeh Maller, University of Massachusetts

The recently completed Two Micron All Sky Survey (2MASS) is the largest catalog of near infrared data, containing more than 500 million stars and 1.6 million extended sources. The near infrared offers us the opportunity to study galaxies in a band where dust obscuration is minimized and for which mass-to-light ratios vary the least. I will discuss large scale structure in 2MASS, focusing on the angular correlation function and the flux dipole we measure using 2MASS galaxies. The flux dipole is 16 degrees from the CMB velocity dipole, where this offset seems to be entirely due to the contribution of the few hundred brightest galaxies. >From comparing the acceleration of the Local Group from the flux dipole with our motion with respect to the CMB I find that K-band selected galaxies are unbiased tracers of the mass distribution. I will show that the angular correlation function of 2MASS galaxies deviates significantly from a pure power law as expected in halo occupation models. Finally I will invert the angular correlation function to determine the power spectrum of K-band selected galaxies which is well fit by a CDM type power spectrum on linear scales.

Priyamvada Natarajan, Yale University

Galaxy-galaxy lensing in clusters provides constraints on properties of early-type galaxy halos. The tidally truncated radii thus inferred from these studies is then used to obtain constraints on the nature of dark matter. Current observations of HST cluster-lenses strongly rule out fluid-like equations of state and are in fact consistent with collisionless dark matter.

Emil Mottola, LANL

The discovery of dark energy comprising some 70% of the energy density of the universe has brought the long-standing cosmological constant problem to the attention of observational cosmologists. The consistent treatment of quantum vacuum energy in gravity and cosmology very likely requires some revision in classical general relativity. The minimal revision required is the inclusion of the trace anomaly of massless fields, whose fluctuations do not decouple from the metric even at the very largest space and time scales. The trace anomaly predicts a conformally invariant phase of gravity, which has consequences for the spectrum and statistics of the CMBR. Conformal invariance leads in general to deviations from naive classical scaling. The spectral index of the two-point function of density fluctuations is given in terms of the quantum trace anomaly and is greater than one, leading to less power at large distance scales than a strict Harrison-Zel'dovich spectrum. Conformal invariance also implies non-gaussian statistics for the higher point correlations and completely determines the large angular dependence of the three-point correlations of the CMBR.

Ishwaree Neupane, University of Taiwan

I discuss the time-dependent compactifications of higher-dimensional gravity models and M-theory with fluxes to generate a potential for the moduli. I analyse some exact complicated scalar potentials for the dimensionally reduced effective theories, present various solutions that lead to a transient period of acceleration of the 4D spacetime(universe),and examine on the possibility of obtaining sufficient inflation by warped and product space complifications, in general. I will also comment upon the cosmic acceleration due to negative powers of curvatures in modified gravity in four and higher dimensions, including some gravitational tests.

Thomas Cox, UC (Santa Cruz)

There is mounting evidence that galaxy interactions play an important role in galaxy evolution. Elliptical galaxies, spiral bulges, and a significant fraction of all the stars in the universe may be byproducts of galaxy mergers, especially mergers at high redshift. In order to better understand the roles mergers play in galaxy evolution we are using high resolution N-body simulations, including hydrodynamics and star formation, to sample the large parameter space of pre-merger galaxy properties and interaction parameters. We briefly discuss how this improves upon previous work in this area and demonstrate how our simulations can be used as inputs to semi-analytic models of galaxy formation. Finally, we show how mock observations of our simulations can provide insight into observations of galaxy spectra and morphologies.