A Decade of Dark Energy

Andreas Albrecht
Steven Allen
Rachel Bean
Chuck Bennett
Gary Bernstein
Chris Blake
James Braatz
Sarah Bridle
Asantha Cooray
Ruth Daly
Daniel Eisenstein
Alex Filippenko
Brenna Flaugher
Wendy Freedman
Henk Hoekstra
Wayne Hu
Lam Hui
Dragan Huterer
Jai-chan Hwang
Bhuvnesh Jain
Saurabh Jha
Robert Kirshner
Lawrence Krauss
Tod Lauer
Mario Livio
Ishwaree Neupane
Lyman Page
John Peacock
William Percival
Saul Perlmutter
Valeria Pettorino
Adam Riess
Paul Steinhardt
Mark Sullivan
Michael Turner
Tony Tyson
Licia Verde
Yun Wang
Scott Watson
Edward Witten

Speaker: Andreas Albrecht (University of California, Davis)
Title: What Can We Learn from Future Dark Energy Probes?
Abstract: I briefly review the fundamental physics motivations for the study of dark energy and then take up the problem of assessing the impact of propose dark energy experiments. I consider in turn a variety of approaches, from forecasting the impact of data on abstract dark energy parameters to exploring its impact on specific scalar field models. The Dark Energy Task Force model data sets are used to provide common points of comparison. I give special emphasis to so recent work that shows that the goal of discriminating among scalar field quintessence models sets concrete thresholds for future dark energy experiments.

Speaker: Steven Allen (KIPAC/SLAC; Stanford)
Title: Cosmological Constraints from X-ray Studies of Galaxy Clusters
Abstract: X-ray observations of galaxy clusters provide one of our most powerful tools to investigate dark energy. I will discuss the latest results from two independent techniques based on X-ray cluster studies. The first uses measurements of the baryonic mass fraction in the largest, dynamically relaxed clusters. This method, like type Ia supernovae studies, measures distance as a function of redshift and traces the acceleration of the Universe directly. It also provides a tight constraint on the mean matter density. The second experiment uses observations of the growth of cosmic structure, as manifested in the evolution of the X-ray luminosity function of galaxy clusters. It leads to tight constraints on the amplitude of mass fluctuations in the Universe, and new constraints on dark energy. I will emphasize the allowances for systematic uncertainties incorporated into these experiments and place the results in the context of other current cosmological data. I also will comment on the prospects for improving these results over the next few years.

Speaker: Rachel Bean (Cornell University)
Title: Dark Energy Dichotomies
Abstract: In addition to Einstein's cosmological constant, a variety of alternative dark energy scenarios are currently under consideration, including particle-based theories and modifications to General Relativity. We will discuss how observations might be employed to distinguish between these different theoretical avenues.

Speaker: Chuck Bennett (Johns Hopkins)
Title: Advanced Dark Energy Physics Telescope (ADEPT)
Abstract: The ADEPT space mission concept uses the CMB-calibrated sound horizon at decoupling as a "standard ruler" by which to measure both the expansion history of the universe, H(z), and the angular diameter distance, in the redshift range 1<2. ADEPT also measures the luminosity distance of high-redshift Type Ia supernovae in a wavelength and redshift range complementary to surveys from the ground. These three measurements (the Hubble parameter, the angular diameter distance, and the luminosity distance) will be inter-compared to assess the level of systematic errors and provide for robust dark energy results. Results will complement ground-based weak lensing data from programs such as from Pan_STARRS and LSST. Further, the ADEPT measurements will improve the ground-based weak lensing experiments by supplying data that enhances the accuracy of their photometric redshift determinations. From the time of Hubble to the most recent 2dFGRS and SDSS observations, galaxy redshift surveys have produced both seminal and wide-ranging astrophysical advances. The ADEPT survey of 100 million galaxy redshifts across the full sky will be, by far, the largest such survey in history.

Speaker: Gary Bernstein (Professor, University of Pennsylvania)
Title: SNAP - An Overview of the Supernova Acceleration Probe (SNAP) Mission
Abstract: An Overview of the Supernova Acceleration Probe (SNAP) Mission

Speaker: Chris Blake (Swinburne University of Technology)
Title: First results from the WiggleZ Galaxy Redshift Survey
Abstract: The WiggleZ project at the Anglo-Australian Telescope is a large-scale redshift survey of UV-selected emission-line galaxies. The survey is mapping a co-moving volume of approximately 1 Gpc^3 at a significantly higher redshift (0.5 < z < 1.0) than has been previously achieved by projects such as the 2dFGRS and SDSS. The main science goal is to use baryon acoustic oscillations in the galaxy clustering pattern as a standard ruler to measure the cosmic distance scale and expansion rate to z=1 and hence perform a robust test of the cosmological constant model. The survey is approximately 50% complete and is scheduled to finish in 2009. I will introduce the project and present initial results on the clustering, environments and luminosity function of high-redshift star-forming galaxies. I will also discuss forecasts for testing dark energy models with WiggleZ in the context of current and future cosmological datasets.

Speaker: James Braatz (NRAO)
Title: The Megamaser Cosmology Project
Abstract: As a complement to observations of the Cosmic Microwave Background, a precise measurement of the Hubble constant would provide a valuable constraint on the equation of state of dark energy. Currently, the best measurements of the Hubble constant are based on standard candle observations and are limited by systematic uncertainties at about the 10% level. Here we describe an ambitious project that aims to determine the Hubble constant with a total uncertainty of 3% by measuring direct, geometric distances to galaxies in the Hubble flow. The technique, pioneered on NGC 4258, is based on observations of circumnuclear water vapor masers at 22 GHz. Maser disks analogous to the one in NGC 4258, but more distant, have been discovered and are now being studied in detail. We will highlight recent results, including observations of UGC 3789 and NGC 6323, that demonstrate the technique is viable for galaxies well into the Hubble flow. We will also discuss prospects for finding additional maser disks and measuring their distances.

Speaker: Sarah Bridle (University College London)
Title: Cosmic Shear: Potential and Prospects
Abstract: I discuss cosmological constraints from cosmic shear and focus on current work in the areas of shear measurement and intrinsic alignments. The GREAT08 Challenge will be launched this summer aiming the problem of extracting shear at communities outside of gravitational lensing, including the computer science community. I also overview the requirements on imaging, spectra and simulations needed to overcome potential contamination of cosmic shear by galaxy intrinsic alignments.

Speaker: Asantha Cooray (Professor, University of California, Irvine)
Title: Uncorrelated Estimates of Dark Energy Equation of State
Abstract: I will give a talk on some of the recent work we have done on how to extract and establish equation of state with supernovae and other cosmological data.

Speaker: Ruth Daly (Professor, Pennsylvania State University)
Title: The Dark Energy Indicator: A Measure of Deviations of w from -1
Abstract: The dark energy indicator provides a tool to measure deviations of the equation of state of dark energy from -1 over the redshift range from zero to one. The indicator is model-independent, and will be shown for the most recently available supernova and radio galaxy data sets. The preliminary results are consistent with a constant equation of state w of -1 from a redshift of zero to about one.

Speaker: Daniel Eisenstein (Steward Observatory)
Title: Baryon Acoustic Oscillations: A Robust and Precise Route to the Cosmological Distance Scale
Abstract: I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. I will present galaxy clustering results from the Sloan Digital Sky Survey that reveal this feature, giving a geometric distance to a redshift of 0.35 and an accurate measurement of Omega matter. I will then discuss the prospects for future redshift surveys to use the acoustic method to map the curvature and expansion history of the Universe and measure the evolution of dark energy.

Speaker: Alex Filippenko (Professor, University of California, Berkeley)
Title: Improving the Low-Redshift Foundations: Results from the Lick Observatory Supernova Search
Abstract: The Lick Observatory Supernova Search (LOSS), conducted with the 0.8-m Katzman Automatic Imaging Telescope (KAIT), has been the world's most successful search for nearby supernovae, having discovered about 700 SNe over the past decade. I will describe the search, the derived supernova rates as a function of SN type and host-galaxy parameters, an improved low-redshift Hubble diagram consisting of about 100 new SNe Ia, and other results from LOSS and its associated photometric and spectroscopic follow-up programs.

Speaker: Brenna Flaugher (Fermilab)
Title: Overview of the Dark Energy Survey
Abstract: The Dark Energy Survey (DES) is designed to take the next step in the understanding of the mystery of dark energy with a deep, near infrared survey of 5000 sq. deg of the Southern Galactic Cap using a new 500M pixel CCD camera on the 4m Blanco telescope at CTIO. The DES collaboration consists of institutions from the US (Fermilab, Chicago, UIUC, LBNL, CTIO, Penn, Michigan, OSU), the UK (UCL, Portsmouth, Cambridge, Edinburgh and Sussex), Brazil, Spain. In the language of the Dark Energy Task Force, DES is a stage III project and will use four complementary techniques: galaxy cluster counts, weak lensing, angular power spectrum and type Ia supernovae to improve the DETF figure of merit by a factor of 4-5. I will present an overview of the DES instrument (DECam) which will be mounted at the prime focus of the Blanco 4m telescope. DECam includes a focal plane of 62 2kx4k CCDs, a five element optical corrector, five filters (g,r,i,z,Y), and the associated infrastructure for operation in a new prime focus cage. To reach redshifts of ~1, we use the 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL) and assembled into four-side buttable modules at Fermilab. DECam will be devoted to the DES for 525 nights over the five year survey (2011-2016) and will otherwise be available to the community as an NOAO facility instrument. The current status of the project will be described.

Speaker: Wendy Freedman (Carnegie Observatories)
Title: Supernovae
Abstract: I will review the use of SNe Ia for luminosity distance determinations, and give an overview of recent measurements using SNe Ia to provide constraints on the acceleration of the universe. In addition, I will discuss the current systematic uncertainties for SNe Ia. I will also present recent results from the Carnegie Supernova Project. A primary goal of the CSP is to provide an i'- band restframe Hubble diagram for type Ia supernovae. The CSP uses the 1-m, 2.5-m and 6.5-m telescopes at Las Campanas, and is aimed at testing for and reducing systematic uncertainties by obtaining a sample of multiwavelength observations over the redshift range 0 < z < 0.7.

Speaker: Henk Hoekstra (University of Victoria)
Title: Recent Results from Weak Gravitational Lensing by Large Scale Structure
Abstract: Intervening structures in the universe give rise to small distortions in the shapes of distant galaxies. By measuring this tiny coherent signal, we can study the mass distribution in the universe directly, without relying on baryonic tracers. This makes weak lensing by large-scale structures a powerful probe of cosmology and dark energy in particular. I will review the topic of "cosmic shear" and discuss how the signal is extracted from the data. I will present results from recent surveys, most notably the CFHT Legacy Survey. Finally I will discuss the prospects of this unique probe to constraint dark energy.

Speaker: Wayne Hu (University of Chicago)
Title: The Cosmology of f(R) Models for Acceleration
Abstract: I will discuss the cosmological implications of f(R) models of alternate gravity from cosmic acceleration to the non-linear regime.

Speaker: Lam Hui (Columbia University)
Title: Magnification Distortion of the Galaxy Correlation Function: Opportunities and Challenges
Abstract: I will demonstrate how gravitational lensing makes the galaxy correlation function anisotropic, and discuss the opportunities and challenges that this effect offers. This anisotropy has a distinctive shape, making it possible to perform a lensing measurement simply by counting galaxies i.e. without the need to measure galaxy shapes. On the other hand, this anisotropy also complicates the interpretation of baryon acoustic oscillation measurements. It can shift the apparent position of the baryon wiggle along the line of sight by up to 3 %, implying a shift in the inferred dark energy equation of state by up to 15%.

Speaker: Dragan Huterer (University of Michigan)
Title: Figures of Merit for Dark Energy Experiments
Abstract: I briefly review the history and discuss current status of how to characterize the intrinsic power of an experiment to probe dark energy.

Speaker: Jai-chan Hwang (Kyungpook National University)
Title: Cosmological Post-Newtonian Approximation with Dark Energy
Abstract: We present general relativistic cosmological hydrodynamic equations with the post-Newtonian (PN) corrections. The PN approximation, based on the assumptions of weak gravitational fields and slow motions, provides a way to estimate general relativistic effects in the fully nonlinear evolution stage of the large-scale cosmic structures. We include the cosmological constant and a minimally coupled scalar field as the potential dark energy. We present the fully nonlinear cosmological 1PN equations in a form suitable for implementation in conventional Newtonian hydrodynamic simulations. Although the typical 1PN order terms are about 10^{-6} - 10^{-4} times smaller than the Newtonian terms, we cannot rule out possible presence of cumulative (secular) effects due to the time-delayed propagation of the relativistic gravitational field with finite speed. These relativistic correction terms could become important in future precision cosmology.

Speaker: Bhuvnesh Jain (Professor, University of Pennsylvania)
Title: Testing Gravity with Lensing and Large-Scale Structure
Abstract: Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. Modified gravity theories have richer observational consequences for large-scale structure than conventional dark energy models, in that different observables are not described by a single growth factor. We discuss tests of gravity from kpc-Gpc scales using dynamics, gravitational lensing and redshift space probes of large-scale structure. We show how a broad class of gravity theories can be tested by combining these observations. We also consider the question: can a clustered dark energy model mimic modified gravity models in all observational tests?

Speaker: Saurabh Jha (Rutgers University)
Title: The SDSS Supernova Survey: Results and Prospects
Abstract: In three seasons, the SDSS SN survey has discovered about 500 spectroscopically confirmed type Ia supernovae with 0.1 < z < 0.4. This redshift range has been only sparsely sampled in the past, despite the importance of connecting the nearby SN samples with those obtained at higher redshifts. We present cosmological results from the first year SDSS SN sample, including constraints on the dark energy equation of state, as well as analysis of supernova rates, intrinsic supernova and host properties, and progenitor studies. We also describe prospects for science with the full SDSS SN survey.

Speaker: Tod R. Lauer (NOAO)
Title: Destiny, the Dark Energy Space Telescope
Abstract: Destiny is a concept for for the NASA/DOE Joint Dark Energy Mission. It will constrain the DE equation of state by conducting both SN Ia and weak-lensing surveys. I will detail the goals of the Destiny Investigation.

Speaker: Mario Livio (STScI)
Title: Dark Energy: Hopes and Expectations
Abstract: I shall review different classes of models for dark energy, in light of the most recent observational results. I shall attempt to evaluate what may be reasonable expectations (as opposed to mere hopes) concerning our understanding of the nature of dark energy in the next decade.

Speaker: Ishwaree Neupane (Canterbury University)
Title: Dark Energy Constraints on Modified Gravities
Abstract: Abstract: Extended theories of gravity involving higher-order curvature terms, or extra dimensions, have been modeled in the past to explain the observationally supported cosmological perturbations, in addition to the resolution of initial singularity and study of bouncing cosmologies. Such models often incorporate a dynamical scalar field coupled to Riemann curvature invariants of a Gauss-Bonnet form. In this talk, I offer discussions on about how to test such a modified scenario of gravity against cosmological and astrophysical observations, including the classical tests of gravity. I will motivate the discussion through insights of non-minimal scalar couplings, crossing of phantom divide and time-varying dark energy equation of state.

Speaker: Lyman Page (Princeton University)
Title: WMAP: Recent Results and Dark Energy
Abstract: The Wilkinson Microwave Anisotropy Probe (WMAP) team recently released data and results from five years of observations. We review the findings and discuss what new we have learned about the early universe, cosmological neutrinos, and the epoch of reionization. We also discuss what we learn about the dark energy from the CMB.

Speaker: John Peacock (Professor, University of Edinburgh)
Title: Dark Conclusions
Abstract: Some concluding remarks will be given, mingling highlights of the meeting with long-standing prejudices of the speaker.

Speaker: John Peacock (Professor, University of Edinburgh)
Title: EUCLID: ESA's Proposed Dark Energy Mission
Abstract: The European Space Agency has a process named "Cosmic Vision" for future space missions in astronomy (and other areas of space science). The first experiment is expected to be a "Medium mission", to be launched in 2017. The budget is approximately 300M Euro from ESA, plus national contributions. One of the proposals competing for this slot is EUCLID: the names honours the pioneer of geometry, rather than being an acronym, and denotes the fact that it is a geometrical probe of dark energy. The mission aims to combine optical imaging of 20,000 deg^2 for gravitational lensing with slit spectroscopy of several x 10^8 galaxies, based on DMD technology, to measure Baryon Acoustic Oscillations.

Speaker: Will Percival (Institute of Cosmology and Gravitation, Portsmouth)
Title: Latest Results from Large-Scale Structure and Baryon Acoustic Oscillation Observations
Abstract: I will review previous analyses of large-scale structure based on the 2dFGRS and SDSS. Limitations will be briefly considered. I will then review baryon acoustic oscillation observations, leading to the latest results from the SDSS. The implications for dark energy, cosmology and cosmological parameters will be discussed.

Speaker: Saul Perlmutter (University of California, Berkeley)
Title: Piecing Together Current Supernova Constraints on Dark Energy
Abstract: As the recent generations of supernova measurements advance towards tighter statistical and systematic constraints on dark energy, we need to perform careful cross-comparison and cross-calibration of subsets of Type Ia supernovae. These subsets are drawn from, e.g., different search campaigns, different redshift ranges, and different host galaxy environments. These comparisons help quantify systematic uncertainties and help identify the most important supernova data still needed to improve the constraints. I will present advances in the current dark energy constraints that result from these supernova studies, as well as some new supernova data sets from ground and space that start to fill in the missing pieces of the analysis puzzle.

Speaker: Valeria Pettorino (Institute for Theoretical Physics, Heidelberg)
Title: Neutrino Clustering in Interacting Dark Energy Cosmologies
Abstract: The case for an interaction between Dark Energy and other components in the Universe (matter, neutrinos, gravity) has recently been object of a wide variety of investigations, aiming at a better understanding of the dark energy issue via its coupling to other species. Within the framework of interacting dark energy, we consider the case in which quintessence interacts with neutrinos, the latter being characterized by a mass that increases with time. We show how growing neutrino cosmologies, which might naturally lead to the observed amount of dark energy today, can be characterized by a substantial neutrino clustering on the scales of superclusters. The presence of neutrino lumps, partially dragging the clustering of dark matter, could represent a peculiar feature of growing neutrino scenarios, possibly detectable via an imprint on the CMB-fluctuations or through the gravitational potential. If observed, large scale non-linear structures might be an indication of a new attractive cosmological interaction.

Speaker: Adam Riess (JHU/STScI)
Title: Dark Energy and The Hubble Constant from HST, Version 2.0
Abstract: The expansion rate and its evolution must be empirically determined for our Universe to reveal its composition, scale, age, and fate. The Hubble Space Telescope is unique in its ability to measure the keystones of cosmic expansion, distant type Ia supernovae and Cepheid variables in their hosts. In 1998, high-redshift SNe Ia provided the first direct evidence for an accelerating Universe and the existence of dark energy. More recently, ACS and NICMOS on HST have become tools to calibrate the Hubble diagram of SNe Ia with modern data and to extend its reach to z>1 when cosmic expansion was still decelerating. I will present the status of a "next generation" effort called SHOES to improve the precision of the Hubble constant measured with HST by the use of a streamlined distance ladder. By observing Cepheids in the near-IR and by minimizing the dominant sources of past systematic uncertainty we expect to reach a precision of ~4%. A measurement of the Hubble constant to a precision of a few percent would be a powerful aid to the investigation of the nature of dark energy and a potent "end-to- end" test of the present cosmological model. Future improvements in measuring the Hubble constant should make it one of the leading constraints on dark energy.

Speaker: Paul Steinhardt (Professor, Princeton University)
Title: Constraining Dark Energy
Abstract: This talk will discuss strategies for constraining models of time-varying dark energy using a combination of astronomical and laboratory measurements.

Speaker: Mark Sullivan (University of Oxford)
Title: Dark Energy Constraints from the Supernova Legacy Survey
Abstract: The CFHT Supernova Legacy Survey (SNLS) is a 2003-2008 program using 400-500 high-redshift (0.2<1.0) Type Ia Supernovae (SNe Ia) to constrain the average equation-of-state parameter of dark energy, w. I will present results from the first three years of the survey, including the latest analyses of the cosmological constraints derived from around 300 SNe Ia combined with recent WMAP5 measurements. I'll also discuss the handling of experimental systematics in the analysis as well as tests for astrophysical systematics enabled by the SNLS dataset, such as evolution in SN Ia properties. Finally, I'll briefly discuss the prospects for SN Ia cosmology surveys planned over the next 5 years in the context of science learned from SNLS.

Speaker: Tony Tyson (Professor, University of California, Davis)
Title: The Large Synoptic Survey Telescope
Abstract: The LSST system is designed to yield high image quality as well as superb photometric accuracy. A deep time domain survey of 20,000 square degrees in six bands from 320 to 1050 nm will image each region 1000 times in ten years of operation. The 27.5 r mag limit enables photometry of ten billion galaxies to low surface brightness and shape measurement of several billion galaxies. A number of independent cross-checking probes of the nature of dark energy will result. Using multiple photometric redshift bins, the joint analysis of 2-D BAO and weak lensing is particularly powerful. These and other unique probes of dark energy involving the deep wide-area time domain data will be described. These LSST probes of dark energy are complementary to JDEM.

Speaker: Licia Verde (Professor, Institute of Space Sciences, Bellaterra)
Title: How Can CMB Help Constraining Dark Energy?
Abstract: Cosmic Microwave Background observations have been fundamental in defining the "standard cosmological model". It is however other probes (e.g., Baryon acoustic oscillations, weak lensing, Supernovae, clusters) that are considered the next frontier in dark energy studies. I will discuss how the CMB, alone or in combination with other probes, can help constraining dark energy.

Speaker: Yun Wang (Professor, University of Oklahoma)
Title: What Figure of Merit Should We Use to Evaluate Dark Energy Projects?
Abstract: Choosing the appropriate figure of merit (FoM) for dark energy (DE) constraints is key in comparing different DE experiments. I will show that for a set of DE parameters {f_i}, it is most intuitive to define FoM = 1/sqrt[det{Cov(f1,f2,f3,...)}], where Cov(f1,f2,f3,...) is the covariance matrix of {f_i}. The {f_i} should have clear physical meaning, and be minimally correlated. I demonstrate two useful choices of {f_i} using current observational data: (1) (w_0,w_{0.5}), values of w_X(a) at z=0 and z=0.5, with w_X(a) = 3w_{0.5}-2w_0+3(w_0-w_{0.5})a; (2) (X_{0.5}, X_{1.0}, X_{1.5}), values of X(z)=rho_X(z)/rho_X(0) at z=0.5, 1.0, and 1.5, assuming X(z>1.5)=X_{1.5}. Parameter set (1) is significantly less correlated than (w0,wa), and parameter set (2) allows us to obtain minimal model independent constraints on dark energy. Future dark energy experiments should be evaluated using their factors of improvement in FoM of both (w_0,w_{0.5}) and (X_{0.5}, X_{1.0}, X_{1.5}).

Speaker: Scott Watson (University of MIchigan)
Title: Inflation and Dark Energy: Is There a Connection?
Abstract: We now have convincing evidence that both today and in the very early universe, the cosmic expansion went through a period of acceleration. A natural question arises: Are these periods of acceleration connected? I will briefly review past attempts to address this question, as well as more recent attempts motivated by the string landscape. In particular, I will discuss a crucial theoretical difficulty that arises in constructing such models, due to the vast range of energy and length scales involved. I will also discuss the possible experimental signatures that may arise if such models can be realized.

Speaker: Ed Witten (Institute for Advanced Study, Princeton)
Title: Models Of Dark Energy
Abstract: The talk will be about the interest, but also the difficulties, of alternatives to the standard model of dark energy -- i.e., the cosmological constant -- and more broadly, about the impact of cosmic acceleration on our views about physics.

Speaker: Gabriel R. Bengochea (IAFE-UBA-CONICET)
Title: Luminosity Distance for Born-Infeld Electromagnetic Waves Propagating in a Cosmological Magnetic Background
Abstract: The discovery of a diminution in the observed energy fluxes coming from supernovae type Ia has opened one of the most puzzling and deepest problems in cosmology today. Although the cosmological constant seems to be the simplest explanation for the phenomenon, several dynamical scenarios have been tried out. We have studied a speculative model by analyzing Born-Infeld electromagnetic waves interacting with a static magnetic background in an expanding universe. Here we show how the non-linear character of Born-Infeld electrodynamics modifies the relation between the energy flux and the distance to the source, which gains a new dependence on the redshift that is governed by the background field. We compute the luminosity distance as a function of the redshift and compare with the Maxwellian curves for supernovae type Ia.

Speaker: Michael Blomqvist (Stockholm University)
Title: Probing Dark Energy Inhomogeneities with Supernovae
Abstract: The search for spatial variations in dark energy properties is an important complement to studies aiming at constraining the time evolution of dark energy. We discuss the possibility to identify anisotropic and/or inhomogeneous cosmological models using type Ia supernova data. A search for correlations in current type Ia peak magnitudes over a large range of angular scales yields a null result. However, the same analysis limited to supernovae at low redshift, shows a feeble anticorrelation at angular scales of about 40 degrees. Upcoming data from, e.g. the SNLS and the SDSS-II supernova searches will improve our limits on the size of - or possibly detect - possible correlations also at high redshift at the percent level in the near future. With data from the proposed SNAP satellite, we will be able to detect the induced correlations from gravitational lensing on type Ia peak magnitudes on scales less than a degree.

Speaker: Wenjuan Fang (Physics Department, Columbia University)
Title: Constraints on Modified Gravity Theories from Existing Geometrical and Large Scale Structure Growth Data
Abstract: The observed acceleration of the cosmic expansion rate could be produced by modifications to general relativity on large spatial scales, rather than by the presence of dark energy. We compute CMB anisotropies in the so--called DGP model for modified gravity, by modifying the public Boltzmann code CAMB to include a parameterized post-Friedmann (PPF) description of the DGP model. We apply the Markov Chain Monte Carlo methods to fit the DGP model (both with and without curvature) to CMB temperature and polarization power spectra, as well as to luminosity distances to Type Ia Supernovae (SN), and Hubble Space Telescope measurements of $H_0$. We find that DGP models give a significantly poorer fit to the combined SNLS+HST+WMAP5 data than LCDM models with the same number of free parameters. The fits favor the LCDM model by a relative likelihood of $-2Delta ln L=28$ (if flat models are assumed with seven free parameter), and by $-2Delta ln L=21$ (when curvature is an 8th free parameter). We also find that in the flat models, $approx$1/3rd of the relative likelihood is contributed by information on growth from the ISW effect, whereas growth accounts for $approx$2/3rd in the curved case.

Speaker: Urbano Franca (IFIC - CSIC/Universidad de Valencia)
Title: Model Independent Constraints on Mass-varying Neutrino Scenarios
Abstract: Models of dark energy in which neutrinos interact with the scalar field responsible for the acceleration of the universe in general imply the variation of the neutrino masses on cosmological time scales. In this work we propose a parameterization for the neutrino mass variation that captures the essentials of those scenarios and allows for constraining them in a model independent way, that is, without resorting to any particular scalar field model. Models in which the neutrino masses were heavier in the past are strongly disfavored, and the results are totally consistent with constant mass neutrinos.

Speaker: Jeffrey Kubo (Fermi National Accelerator Laboratory)
Title: Statistics of Dark Matter Halos in the Deep Lens Survey
Abstract: One proposed method with which future optical imaging surveys will constrain cosmological parameters, including dark energy, is with a survey of shear-selected galaxy clusters. In this method, peaks in the matter distribution are identified as a function of their signal-to-noise from weak lensing `mass' maps. Current deep optical surveys, such as the Deep Lens Survey are producing the first such maps from weak lensing. Here we present a weak lensing map of the Deep Lens Survey F2 field covering an area of four square degrees. To reconstruct the projected mass in this field we use a maximum likelihood approach which overcomes issues associated with traditional 'direct' methods of mass reconstruction. We present properties of high signal-to-noise dark matter peaks detected in the F2 field, as well as the global distribution of these peaks.

Speaker: Tsz Yan Lam (University of Pennsylvania)
Title: The Probability Distribution Function of Dark Matter in Redshift Space and a Reconstruction Method for the Initial Distribution Function
Abstract: The ellipsoidal collapse model is a modification of the Zeldovich Approximation which specifies how an initial fluctuation field can be mapped to a final one, even when the mapping is rather nonlinear. I show how this allows an accurate prediction of the real and redshift space smoothed dark matter probability distribution functions. This mapping also motivates a method for reconstructing the initial field from the nonlinear one. Application of this method to the highly non-Gaussian non-linear density field in a numerical simulation yields an accurate estimate of the initial Gaussian field from which it evolved.

Speaker: Adam Mantz (KIPAC)
Title: Constraints on Dark Energy from the Growth of Structure Observed in X-ray Luminous Galaxy Clusters
Abstract: The growth of cosmic structure is a sensitive probe of cosmology, including dark energy or modified gravity. X-ray emission from the baryonic content of massive clusters of galaxies provides a means to measure the growth of structure in these large systeThanks to the ROSAT All Sky Survey, hundreds of massive, X-ray luminous clusters out to redshift z~1 have been cataloged. Using this data, we have obtained constraints on the dark matter density, amplitude of density perturbations, and dark energy equation of state which are consistent with the concordance model of cosmology. This method is complementary to other cosmological observations; in combination with cosmic microwave background, supernova and cluster gas fraction data, the constraint on the dark energy equation of state approaches the 5% level.

Speaker: Jeffrey Newman (University of Pittsburgh)
Title: Calibrating Photometric Redshifts for Dark Energy Experiments with Cross-Correlation Techniques
Abstract: To place constraints on the dark energy equation of state, many proposed experiments will rely critically on redshift distributions determined from photometric redshifts. The requirements are very stringent - redshift calibration uncertainties must be below 0.002(1+z) for Stage IV experiments. It is unlikely that it is possible to obtain such a robust calibration using conventional methods, as all deep spectroscopic samples are substantially (typically 10%-50% or more) incomplete, in a manner that depends on galaxy luminosity and color, even at magnitudes much shallower than future experiments will probe. In this talk, I present a new method which can meet the calibration requirements for future experiments with existing and currently-planned spectroscopic datasets; incomplete spectroscopy of the brightest objects at a given z is sufficient for this technique. Specifically, the clustering between galaxies in a photometric redshift bin and a spectroscopic sample, measured as a function of spectroscopic z, allows us to determine the true redshift distribution of objects in the bin to high accuracy, meeting or exceeding the calibration requirements of Stage IV experiments with realistic redshift samples.

Speaker: Rob Olling (University of Maryland)
Title: Accurate Extragalactic Distances and Dark Energy
Abstract: I discuss how the current and future uncertainty on H_0 affects the uncertainty in the equation of state (EOS) of dark energy (DE) (w). The same procedure yields an estimate for the attainable accuracy on the total- and curvature densities of the Universe. Also, a direct determination of H_0 provides a direct measure of the critical density. I present two limiting cases. In the more unrealistic case, the constraints provided by "additional" data do not improve significantly, while the error on H_0 is decreased by factors 2 -- 10. The other case, with improved additional data but with current H_0 errors has been investigated by the Dark Energy Task Force (DETF). In the former scenario, a PLANCK-like CMB determination hardly changes the accuracy with which w and Omega_tot are determined, unless H_0 is determined to a few percent. The DETF concluded that H_0 accuracy hardly matters if the additional data are sufficiently accurate. However, moderate H_0 improvements combined with moderately improved "other" data might significantly constrain the evolution of DE, but at a reduced cost and/or at a quicker pace. Also, this would avoid the very unattractive (and unnecessary, really) H_0-marginalization procedure. Several methods can yield extragalactic distances with errors of the order of several per cent: I discuss the current and future strengths and weaknesses of these methods. Specifically I review methods based on: 1) the velocity field, 2) maser, 3) light echoes, 4) binary stars, and 5) the "rotational parallax" (RP). These methods rely on geometry rather than astrophysics or cosmology, so that their results are robust. Time permitting, I will describe the RP technique which can provide accurate (1%), single-step and bias-free distances to Local Group galaxies. These distances set the zero-points for other distance indicators which in turn would yield H_0. Achieving an accuracy of a few per cent for M31, M33 and the LMC requires +/- 10 km/s radial velocities and proper motions from future astrometric missions such as SIM and possibly GAIA.

Speaker: Linda Ostman (Stockholm University)
Title: Estimating Dust Extinction in Distant Galaxies Using Quasars
Abstract: We report on how observations of quasars shining through foreground galaxies offer a way to probe the dust extinction curves of distant galaxies. We compare the observed colours of quasars reported in the literature with spectral templates reddened by different extinction laws and dust properties. We measure a difference in rest-frame B-V between the quasar images we study, and quasars without resolved foreground galaxies. This difference in colour is indicative of significant dust extinction in the intervening galaxy. Good fits to standard extinction laws were found for 22 images, corresponding to 13 different galaxies. Our fits imply a wide range of possible values for the total-to-selective extinction ratio, Rv. The distribution was found to be broad with a weighted mode of 2.4 and a FWHM of 2.7. Thus the bulk of the galaxies for which good reddening fits could be derived, have dust properties compatible with the Milky Way value (Rv=3.1).

Speaker: David Rapetti (KIPAC, SLAC/Stanford)
Title: Probing Dark Energy Using Future X-ray Galaxy Cluster Data
Abstract: Forthcoming large X-ray or SZ galaxy cluster surveys, from missions such as eROSITA-SpectrumRG or SPT/ACT/Planck, respectively, will find hot, X-ray luminous clusters out to high redshifts. Short snapshot observations with a new X-ray observatory with capabilities similar to those planned for the Constellation-X mission should then be able to identify a sample of ~500 hot (kT>~5keV), suitably relaxed systems; and later re-observed them with longer exposures (~20ks per cluster on average) to measure the X-ray gas mass fraction, fgas, to a precision of ~5 per cent. We examine the ability to constrain dark energy using such an fgas sample, and find that the fgas experiment offers a competitive and complementary approach to the best other large, planned dark energy experiments with a comparable Dark Energy Task Force figure of merit. If time permits, I will also present preliminary, new constraints on gravity at cosmological scales. For this analysis we use a convenient parameterization of departures from the current gravity theory, General Relativity, and present-day measurements of the growth of cosmic structure in X-ray luminous galaxy clusters from the MACS, BCS and REFLEX X-ray cluster samples.

Speaker: Thomas Reiprich (Argelander Institute for Astronomy)
Title: Studying the Nature of Dark Energy with Galaxy Clusters
Abstract: I'll present the latest results from our Chandra and XMM-Newton (and Suzaku) follow-up of a complete sample of the 60 X-ray brightest clusters in the sky (HIFLUGCS). Furthermore, I'll report on the status of the weak lensing follow-up of the luminous and high-z subsample of 40 clusters from the 400 square degree survey. The combination of both samples will be used to constrain the nature of dark energy through the evolution of the cluster mass function and merger frequency. Moreover, these high quality observations will be vital to constrain the observable--mass relations required for near future large X-ray cluster surveys like eROSITA.

Speaker: Shun Saito (University of Tokyo)
Title: Impact of Massive Neutrinos on Nonlinear Clustering and Degeneracy with Dark Energy Parameter
Abstract: Future galaxy redshift surveys will open up an exciting opportunity for precision determinations of neutrino masses as well as dark energy parameter, w. Neutrino mass and w can be measured by probing the neutrino free-streaming scale and the baryon acoustic oscillation (BAO) scale, respectively. It is discussed that expected neutrino mass and w are degenerate because neutrino free-streaming scale is comparable to BAO scale, where nonlinear clustering cannot be neglected. In the literature, however, recent progress of nonlinear theory does not include the effect of neutrino free-streaming. In this talk, we present the new approach to include properly the non-linear gravitational evolution of matter power spectrum for a mixed dark matter model (neutrinos plus cold dark matter). Based on the perturbation theory, we show that the suppression of the power spectrum amplitude caused by massive neutrinos is enhanced in the weakly nonlinear regime where standard linear theory ceases to be accurate. Due to this enhanced effect and the gain in the applicable range of the model prediction, the nonlinear model may enable a precision of sigma(m_tot)~0.09eV in constraining the total neutrino mass for the planned galaxy redshift survey, a factor 2.5 improvement compared to the linear regime. Moreover, this improvement leads to berak the degeneracy between neutrino mass and w. Thus, the refined model prescription offers a vital opportunity to determine both the neutrino masses and dark energy parameter.

Speaker: Douglas Snyder
Title: Is Dark Energy Composed of Photons with Negative Mass (Dark Photons)?
Abstract: Dark energy may be composed of photons with negative inertial and gravitational mass. Since the photons comprising dark energy would have negative mass, they could not be observed even though they exert a repulsive gravitational force on entities that have positive mass. Furthermore, dark photons possess little mass which is a feature of dark energy. Dark photons are small enough to comprise the needed density to support a universe that is close to flat. They also may allow for repelling entities with positive mass while they are attracted to entities with positive mass, a possible requirement of dark energy.

Speaker: Michael Wood-Vasey (Harvard University)
Title: Type Ia Supernovae Over A Decade in Wavelength
Abstract: We present preliminary cosmological results from the 6-year ESSENCE supernova survey and discuss our recent work on addressing the current dominant systematic challenge in SN Ia cosmology: distinguishing the nature of dust in supernova host galaxies from the intrinsic color-luminosity variation of SNe Ia. Using data from Swift satellite (UV) and the FLWO 48" (optical) and PAIRITEL (NIR) telescopes at Mt. Hopkins, we are improving our understanding of SNe Ia and beginning to constrain the nature of dust in other galaxies. We find that the NIR H-band is a promising standard-candle reference to determine the impact of intrinsic color and absolute luminosity of SNe Ia and that multiwavelength data is key in separately measuring the dust properties of host galaxies along the line-of-sight to SNe Ia. The next few years should bring significant breakthroughs in this understanding and improvements in our in the use of SNe Ia for determining the nature of dark energy.

Speaker: Hu Zhan (University of California at Davis)
Title: Four LSST Probes of Dark Energy
Abstract: The half-sky LSST six band survey of four billion galaxies will address dark energy physics by exploiting a diversity of precision probes: Weak lensing tomography (WL) of shear vs. redshift, which probes both distances and the evolution of structure vs. redshift, setting multiple constraints on dark energy. Baryon Acoustic Oscillations (BAO) in galaxy spatial correlations measure distances vs. redshift using the “standard ruler” of the peak in the correlation of dark matter revealed in the temperature anisotropies in the cosmic microwave background (CMB). The redshift distribution of shear peaks due to large structures of dark matter (via WL combined with the optical data) are a potentially sensitive probe of dark energy. Tens of thousands of well-observed supernovae are complementary for probing the recent cosmic era when dark energy becomes dominant. These diverse probes are complementary, removing degeneracies. They form interlocking checks on cosmological models and the physics of dark energy. The joint analysis of BAO and WL is especially powerful, because it utilizes all combinations of galaxy and shear correlations to reduce the uncertainties in the galaxy bias and photo-z error distribution. Astrophysical observations are susceptible to systematics, so the LSST is being specifically designed and engineered to minimize and control systematics at a level ten times below the smallest signal of interest. Systematic error experiments using the Subaru telescope are incorporated in these estimates.

Harry Ferguson
Norbert Pirzkal
Jonathan Bagger
Chuck Bennett
Van Dixon
S. Michael Fall
Andrew Fruchter
Benne Holwerda
Mario Livio
Duccio Macchetto
Warren Moos
Marc Postman
Neill Reid
Adam Riess
Massimo Robberto
Massimo Stiavelli