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Event
Science Writer's Workshop
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Spring Symposium 2008
Listing of Talk Abstracts
| What Can We Learn from Future Dark Energy Probes? |
| Andreas Albrecht (UC Davis) |
| 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.
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| Cosmological Constraints from X-ray Studies of Galaxy Clusters |
| Steven Allen (KIPAC/SLAC; Stanford) |
| 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.
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| Dark Energy Dichotomies |
| Rachel Bean (Cornell University) |
| 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. |
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| Advanced Dark Energy Physics Telescope (ADEPT) |
| Dr.
Chuck Bennett (Johns Hopkins) |
| 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
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| SNAP - An Overview of the Supernova Acceleration Probe (SNAP) Mission |
| Prof.
Gary Bernstein (University of Pennsylvania) |
| An Overview of the Supernova Acceleration Probe (SNAP) Mission |
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| First results from the WiggleZ Galaxy Redshift Survey |
| Dr.
Chris Blake (Swinburne University of Technology) |
| 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. |
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| The Megamaser Cosmology Project |
| Dr.
James Braatz (NRAO) |
| 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. |
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| Cosmic Shear: Potential and Prospects |
| Dr.
Sarah Bridle (University College London) |
| 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.
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| Uncorrelated Estimates of Dark Energy Equation of State |
| Prof.
Asantha Cooray (UC Irvine) |
| 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. |
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| The Dark Energy Indicator: A Measure of Deviations of w from -1 |
| Prof.
Ruth Daly (Penn State University) |
| 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. |
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| Baryon Acoustic Oscillations: A Robust and Precise Route to the Cosmological Distance Scale |
| Dr.
Daniel Eisenstein (Steward Observatory) |
| 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.
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| Improving the Low-Redshift Foundations: Results from the Lick Observatory Supernova Search |
| Prof.
Alex Filippenko (UC Berkeley) |
| 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. |
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| Overview of the Dark Energy Survey |
| Ms.
Brenna Flaugher (Fermilab) |
| 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. |
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| Supernovae |
| Dr.
Wendy Freedman (Carnegie Observatories) |
| 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. |
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| Recent Results from Weak Gravitational Lensing by Large Scale Structure |
| Dr.
Henk Hoekstra (University of Victoria) |
| 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. |
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| The Cosmology of f(R) Models for Acceleration |
| Wayne Hu (University of Chicago) |
| I will discuss the cosmological implications of f(R) models of alternate gravity from cosmic acceleration to the non-linear regime. |
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| Magnification Distortion of the Galaxy Correlation Function: Opportunities and Challenges |
| Mr.
Lam Hui (Columbia University) |
| 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%.
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| Figures of Merit for Dark Energy Experiments
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| Dr.
Dragan Huterer (University of Michigan) |
| I briefly review the history and discuss current status of how to
characterize the intrinsic power of an experiment to probe dark energy.
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| Cosmological Post-Newtonian Approximation with Dark Energy |
| Dr.
Jai-chan Hwang (Kyungpook National University) |
| 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. |
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| Testing Gravity with Lensing and Large-Scale Structure |
| Prof.
Bhuvnesh Jain (Univ. of Pennsylvania) |
| 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? |
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| The SDSS Supernova Survey: Results and Prospects |
| Saurabh Jha (Rutgers University) |
| 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.
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| Destiny, the Dark Energy Space Telescope |
| Dr.
Tod R. Lauer (NOAO) |
| 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. |
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| Dark Energy: Hopes and Expectations |
| Dr.
Mario Livio (STScI) |
| 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. |
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| Dark Energy Constraints on Modified Gravities |
| Dr.
Ishwaree Neupane (Canterbury University) |
| Abstract: Extended theories of gravity involving higher-order curvature terms, or extra dimensions, have been modelled 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. |
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| WMAP: Recent Results and Dark Energy |
| Lyman Page (Princeton University) |
| 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. |
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| Dark Conclusions |
| Prof.
John Peacock (University of Edinburgh) |
| Some concluding remarks will be given, mingling highlights of the meeting with long-standing prejudices of the speaker. |
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| EUCLID: ESA's Proposed Dark Energy Mission |
| Prof.
John Peacock (University of Edinburgh) |
| 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.
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| Latest Results from Large-Scale Structure and Baryon Acoustic Oscillation Observations |
| Dr.
Will Percival (Institute of Cosmology and Gravitation, Portsmouth) |
| 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.
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| Piecing Together Current Supernova Constraints on Dark Energy |
| Dr.
Saul Perlmutter (UC, Berkeley) |
| 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. |
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| Neutrino Clustering in Interacting Dark Energy Cosmologies |
| Dr.
Valeria Pettorino (Institute for Theoretical Physics, Heidelberg) |
| 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. |
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| Dark Energy and The Hubble Constant from HST, Version 2.0 |
| Dr.
Adam Riess (JHU/STScI) |
| 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. |
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| Constraining Dark Energy |
| Prof.
Paul Steinhardt (Princeton University) |
| This talk will discuss strategies for constraining models of time-varying dark energy using a combination of astronomical and laboratory measurments. |
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| Dark Energy Constraints from the Supernova Legacy Survey |
| Dr.
Mark Sullivan (University of Oxford) |
| The CFHT Supernova Legacy Survey (SNLS) is a 2003-2008 program using 400-500 high-redshift (0.2
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| The Large Synoptic Survey Telescope |
| Prof.
Tony Tyson (UC Davis) |
| 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. |
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| How Can CMB Help Constraining Dark Energy? |
| Prof.
Licia Verde (Institute of Space Sciences, Bellaterra) |
| 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. |
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| What Figure of Merit Should We Use to Evaluate Dark Energy Projects? |
| Prof.
Yun Wang (Univ. of Oklahoma) |
| 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}).
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