KICP Friday Noon Seminars: 2009
DateTalk TitleSpeaker
January 9, 2009A potpourri of lithium problemsKenneth M Nollett, Argonne National Laboratory
January 16, 2009Precision Cosmology in the Next Decade: Origin of Cosmic Acceleration from CMB and Large Scale Structure SurveysAmir Hajian, Princeton University
January 23, 2009Multi-component dark matterKathryn Zurek, FNAL
January 30, 2009Cosmology and the LHCCarlos E.M. Wagner, Argonne National Laboratory and Univ. of Chicago
February 6, 2009Star Formation in the Early UniverseJarrett L Johnson, The University of Texas at Austin
February 13, 2009The Non-linear Evolution of the Cosmic Microwave BackgroundCyril Pitrou, University of Oslo, Norway
February 20, 2009An Early Look at the Fermi Blazar PopulationStephen E. Healey, Stanford University / KIPAC
February 27, 2009First-order distributed Fermi acceleration of cosmic ray hadrons in non-uniform magnetic fieldsReinhard Schlickeiser, Ruhr-University Bochum
March 6, 2009The Extragalactic Radio BackgroundJack Singal, KIPAC / Stanford University
March 13, 2009Structure Formation in the First Billion Years of the UniverseTom Abel, KIPAC/Stanford
April 3, 2009Wandering in the Hyperfine Forest (Presentation given by Jeff McMahon and Eric Switzer)Jeff McMahon, The University of Chicago
April 10, 2009The Galaxy in Gamma Rays: Results from VERITASBrian Humensky, The University of Chicago
April 17, 2009PlanckGraca M M S T Rocha, Jet Propulsion Laboratory - Caltech
April 24, 2009Black Hole Mergers and Electromagnetic CounterpartsBence Kocsis, Institute for Advanced Study
May 1, 2009CMB Lensing - Constraints on Dark Energy and NeutrinosRoland de Putter, UC Berkeley/Berkeley Lab
May 8, 2009Constraining the inflationary paradigm with current and future dataMaria Beltran, The University of Chicago
May 15, 2009The measurement of Cosmic Ray Electrons from 20 GeV to 1 TeV using the Fermi Large Area TelescopeJonathan F. Ormes, University of Denver
May 22, 2009The Cosmic Microwave Background, Interferometry, and PolarizationJonathan Sievers, CITA
May 29, 2009Observational Constraints on Gravitational Wave Recoil Kick Velocities in Supermassive Black Hole Binaries from Radio GalaxiesC.C. Teddy Cheung, NASA GSFC
June 5, 2009New Results on CMB Polarization from BICEP and QUaDClem Pryke, The University of Chicago
October 2, 2009A preview of upcoming results from the South Pole TelescopeTom Crawford, The University of Chicago
October 9, 2009Galaxies in the Young Universe: Metallicity, Kinematics, and Gas FlowsDawn Erb, UCSB
October 16, 2009Testing General Relativity on Cosmological Scales with Weak Gravitational LensingAli Vanderveld, Caltech/JPL
October 23, 2009Signals from the Cosmological Recombination EpochJens Chluba, CITA
October 30, 2009Satellite Galaxies in LambdaCDM: Orbits, Merging & DisruptionAndrew Wetzel, UC Berkeley
November 6, 2009Cosmological hydrogen recombination: the effect of extremely high-n states and forbidden transitionsDaniel Grin, California Institute of Technology
November 13, 2009Probing the Physics of the Beginning: Primordial Non-Gaussianity and Gravitational WavesAmit Yadav, Institute for Advanced Study, Princeton
November 20, 2009Recent Results on Dark Matter Searches with FermiSimona Murgia, SLAC/KIPAC
December 4, 2009New Results for Giant Arc Statistics in ~100 ClustersAssaf Horesh, Tel-Aviv University

A potpourri of lithium problems
January 9, 2009 | LASR Conference Room | 12:00 PM
Kenneth M Nollett, Argonne National Laboratory

The restricted set of nucleosynthetic sites for lithium and its fragility once produced make it a useful probe of astrophysics, particularly for the big bang and for circulation within stars. There are several outstanding problems in understanding lithium abundances, including turnoff stars with too little lithium and unexpected isotopic ratios (ostensibly from the big bang), giant stars with too much lithium, and main-sequence stars with abundances that are just puzzling. I will discuss these phenomena, emphasizing the big-bang and giant-star lithium problems.

Precision Cosmology in the Next Decade: Origin of Cosmic Acceleration from CMB and Large Scale Structure Surveys
January 16, 2009 | LASR Conference Room | 12:00 PM
Amir Hajian, Princeton University

Observational tests of cosmology during the last decade have brought in a new era of precision cosmology. The concordance model is consistent with various independent astrophysical observations and is specified by a handful of parameters. Although these parameters have been observationally constrained to high precision, there are still important open questions in cosmology, such as: what is the origin of cosmic acceleration?
In the first half of this talk, I will talk about how this question can be addressed by making use of the future CMB data and surveys of large scale structure like galaxy redshift surveys and clusters of galaxies that are going to be available in the next few years. Making precise measurements of the parameters of our cosmological models relies partly on our ability to optimally analyze the high resolution CMB maps. In the second half of my talk I will discuss difficulties of estimating the power spectrum from maps of (specially ground based) CMB experiments and will present a fast and (close to optimal) method to do so.

Multi-component dark matter
January 23, 2009 | LASR Conference Room | 12:00 PM
Kathryn Zurek, FNAL

Exotic new particles, such as axions or WIMPs, offer the best explanation for the cold dark matter which fills the universe. To this point, most of the focus has been on very simple dark matter sectors, with a single new stable elementary state.
Some of the recent observations, if they are to be explained by particle dark matter, suggest that the dark sector may not be so simple. The ATIC and PAMELA experiments, for example, observe an excess of cosmic ray positrons which may potentially be the annihilation products of dark matter. The types of dark matter candidates which generate these signals often arise in theories where the dark matter sector is more complex. We discuss models of dark matter with multiple components of dark matter and new dark forces which generate these signals, and we discuss the implications for dark matter detection experiments.

Cosmology and the LHC
January 30, 2009 | LASR Conference Room | 12:00 PM
Carlos E.M. Wagner, Argonne National Laboratory and Univ. of Chicago

The LHC is expected to shed light on the physics behind the mechanism of electroweak symmetry breaking, associated with the generation of mass of all known elementary particles. There are good reasons to think that the same physics is responsible for the origin of dark matter and, perhaps, of the observable matter-antimatter asymmetry. In this talk I will summarize the arguments that support the above statements and provide a few examples of the interplay between cosmology and collider physics at the LHC.

Star Formation in the Early Universe
February 6, 2009 | LASR Conference Room | 12:00 PM
Jarrett L Johnson, The University of Texas at Austin

One of the outstanding goals of cosmology is to understand how the universe was transformed from its simple state at the end of the Cosmic Dark Ages to the complex state that is observed at the end of reionization. I will discuss the emerging theoretical picture of how the first generations of stars form and how they, in turn, impact the formation of the earliest galaxies. An important task for the coming years is to connect this picture with the observational data, both direct and indirect, that are becoming available. Direct observations will be made with the James Webb Space Telescope, and indirect studies using stellar archaeology will be enhanced with surveys such as SEGUE. I will discuss current efforts to test our theoretical view of star formation in the early universe using these observations.

The Non-linear Evolution of the Cosmic Microwave Background
February 13, 2009 | LASR Conference Room | 12:00 PM
Cyril Pitrou, University of Oslo, Norway

Non-Gaussian effects in the cosmic microwave background (CMB) can arise either from the primordial phase of the universe or from the subsequent non-linear evolution. I will focus on the latter point and review the perturbation theory beyond linear order. I will detail how the kinetic theory can be used in cosmology to derive the evolution of perturbations for polarized radiation. Finally I will present why the collapse of dark matter is the main source of non-Gaussianity in the CMB on small scales.

An Early Look at the Fermi Blazar Population
February 20, 2009 | LASR Conference Room | 12:00 PM
Stephen E. Healey, Stanford University / KIPAC

In the first few months of its operation, the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has detected several hundred sources, dominated at high Galactic latitudes by gamma-ray blazars. I will briefly described the recently issued Fermi Bright AGN Source List and comment some of the properties of the blazar populations seen by the LAT. I will also discuss some of our ongoing work and speculate on future AGN results from Fermi.

First-order distributed Fermi acceleration of cosmic ray hadrons in non-uniform magnetic fields
February 27, 2009 | LASR Conference Room | 12:00 PM
Reinhard Schlickeiser, Ruhr-University Bochum

Large-scale spatial variations of the guide magnetic field of interplanetary and interstellar plasmas give rise to the adiabatic focusing term in the Fokker-Planck transport equation of cosmic rays.
As a consequence of the adiabatic focusing term, the diffusion approximation to cosmic ray transport in the weak focusing limit leads to first-order Fermi acceleration of energetic particles if the product $HL$ of the cross helicity state of Alfvenic turbulence $H$ and the focusing length $L$ is negative. Besides the formal derivation of this acceleration process, the basic physical mechanisms for this new acceleration process are clarified and the astrophysical conditions for efficient acceleration are investigated. It is shown that in the interstellar medium this mechanism preferentially accelerates cosmic ray hadrons over 10 orders of magnitude in momentum. Due to heavy Coulomb and ionisation losses at low momenta, injection or preacceleration of particles above the threshold momentum $p_csimeq 0.17Z^{2/3}$ GeV$/c$ is required.

The Extragalactic Radio Background
March 6, 2009 | LASR Conference Room | 12:00 PM
Jack Singal, KIPAC / Stanford University

Recent results from the ARCADE 2 experiment reveal an extragalactic radio background. This measured background is in excess of the estimated integrated contribution of discrete extragalacic radio sources, with the calculated discrete source contribution being less than 20% of the total background at 1 GHz. Combining the ARCADE 2 measurements at 3 to 90 GHz with a new analysis of existing lower frequency radio surveys shows the residual radio background to have a power law spectrum with spectral index -2.56 +/- 0.04 and a reference temperature of 1.06 +/- 0.11 K at 1 GHz.



I will present the measurement performed by the balloon-borne ARCADE 2 experiment, discuss the techniques for modeling and subtracting the component of the emission originating from the Milky Way Galaxy, and the estimates of the extragalactic discrete source contribution. I will also present the new constraints on CMB spectral distortions and Galactic microwave emission, including the determination that a spinning dust component comprises 40% of the Galactic plane emission at 22 GHz.

Structure Formation in the First Billion Years of the Universe
March 13, 2009 | LASR Conference Room | 12:00 PM
Tom Abel, KIPAC/Stanford

Ab initio modeling of the formation of structure in the Universe is leading to detailed predictions of the nature of the first stars and the first galaxies. These calculations give useful constraints to the history of cosmological reionization and early chemical enrichment. They are constrained by properties of low redshift faint dwarf galaxies, the abundances of heavy elements found in low metallicity stars in the halo of the Galaxy, the optical depth to electron scattering to the CMB, future 21cm tomography, etc.. An adaptive ray tracing algorithm implemented in our adaptive mesh refinement cosmological simulation code is a crucial new ingredient in such simulations of early structure formation. It solves the full radiation hydrodynamical equations and scales with the logarithm of the number of radiation sources models. I will also briefly discuss our efforts of magneto-radiation-hydrodynamical modeling of star formation in clusters within our own Galaxy as a stepping stone towards simulations that compute the formation of galaxies, one star at a time.

Wandering in the Hyperfine Forest (Presentation given by Jeff McMahon and Eric Switzer)
April 3, 2009 | LASR Conference Room | 12:00 PM
Jeff McMahon, The University of Chicago

There has been much excitement recently about 21 cm radiation as an observable of both the reionization era and large scale structure at redshifts roughly z=1 to z=0. A natural question is whether there are other cosmologically observable hyperfine transitions. In the first part of this research talk, we give an overview of the atomic hyperfine transitions and then restrict to the
8.7 GHz transition of 3He+ as an observable of He+ reionization [Eric Switzer]. In the second half of the talk, we return to the 21 cm emission from galaxies [Jeff McMahon]. There are several proposed mapping experiments to measure the 21 cm emission from galaxies to constrain the scale of baryon acoustic oscillations. We consider an alternative approach of integrating down along a sparse array of sight lines which can be arranged to maximize sensitivity to the BAO scale.
These are both active research projects, so questions and criticism are encouraged.

The Galaxy in Gamma Rays: Results from VERITAS
April 10, 2009 | LASR Conference Room | 12:00 PM
Brian Humensky, The University of Chicago

VERITAS, the Very Energetic Radiation Imaging Telescope Array System, is a ground-based observatory for studying nonthermal astrophysics in the gamma-ray band above 100 GeV. The complete four-telescope array has been operating at the Fred Lawrence Whipple Observatory in southern Arizona, USA since the spring of 2007. Observations of galactic sources - including supernova remnants, pulsar wind nebulae, X-ray binaries, and a survey of the Cygnus region - have proven extremely fruitful. Key results include the discovery of VHE emission from the supernova remnant IC 443, studies of the surprisingly variable X-ray binary system LS I
+61 303, and the discovery of variability in the unidentified source
HESS J0632+057. The Fermi Gamma-ray Space Telescope, launched in June 2008, has opened a new window on gamma-ray astronomy in the complementary band between 100 MeV and 100 GeV. This talk will discuss these early VERITAS results and the interplay between Fermi and VERITAS in the study of galactic gamma-ray sources.

Planck
April 17, 2009 | LASR Conference Room | 12:00 PM
Graca M M S T Rocha, Jet Propulsion Laboratory - Caltech

Planck satellite is designed to image the anisotropies of the Cosmic Background Radiation over the whole sky, with unprecedented sensitivity and angular resolution. It has been selected as a third Medium Sized Mission (M3) of ESA's Horizon 2000 Scientific Programme, and it is today part of its Cosmic Vision Programme. Planck will provide a major source of information relevant to Cosmology and Astrophysics. It will test theories of the early universe and the origin of cosmic structure and will provide surveys of both galactic and extragalactic emission at arcminutes angular resolution. Planck will be launched together with the Herschel satellite. After launch Planck and Hershel will separate and will be placed in different orbits around the second lagrangian point of the Earth-Sun System. In this talk I will give an overview of Planck instrument and its expected science output.

With Planck launch imminent (presently scheduled for the 6th of May), we are looking forward to exciting times for CMB cosmologists.

Black Hole Mergers and Electromagnetic Counterparts
April 24, 2009 | LASR Conference Room | 12:00 PM
Bence Kocsis, Institute for Advanced Study

The anticipated detection of the gravitational waves (GWs) by the future Laser Interferometric Space Antenna (LISA) will constitute a milestone for fundamental physics and astrophysics. While the GW signatures themselves will provide a treasure trove of information, if the source can be securely identified in electromagnetic (EM) bands, this would open up entirely new scientific opportunities, to probe fundamental physics, astrophysics, and cosmology. I will describe several mechanisms that might produce EM variability during a SMBH merger. In particular, the binary may produce a roughly periodic variable electromagnetic ?ux, due to the orbital motion prior to coalescence, a transient signal caused by shocks in the circumbinary disk when the SMBH binary recoils and ”shakes” the disk, or a prompt EM flare caused by the viscous dissipation of GWs in the ambient gas. I will discuss whether these time-variable EM signatures may be detectable using a LISA-triggered EM counterpart search campaign.

CMB Lensing - Constraints on Dark Energy and Neutrinos
May 1, 2009 | LASR Conference Room | 12:00 PM
Roland de Putter, UC Berkeley/Berkeley Lab

Weak gravitational lensing of the cosmic microwave background (CMB) by large scale structure along the line of sight shuffles the pattern of temperature and polarization anisotropies on the sky. This makes the CMB sensitive to physics that affects the growth of structure at z=1-4, like massive neutrinos and dark energy. In this talk, I will review how gravitational lensing distorts the CMB power spectra and how the lensing signal can be extracted from the observed anisotropies. I will then discuss prospected constraints from CMB lensing by future probes like Planck and CMBpol on three types of physics beyond standard LCDM: massive neutrinos, ordinary dynamical dark energy and early dark energy. I will also compare the constraining power of two methods for extracting the lensing signal from the CMB: smearing of power spectra vs the optimal quadratic estimator of the lensing potential power spectrum.

Constraining the inflationary paradigm with current and future data
May 8, 2009 | LASR Conference Room | 12:00 PM
Maria Beltran, The University of Chicago

The inflationary paradigm was proposed more than two decades ago.
Although a voluminous amount of cosmological data allows us to impose tight constraints on the inflationary mechanism, the model is by no means fixed yet.
I will briefly review the current status of our understanding of the inflationary process and what could we expect to learn from future CMB experiments.
In particular, I will focus on the possibility that no primordial tensor modes are observed. I will show that, in this case, one could appeal to the curvaton inflationary model and rely in other observables such as the primordial non-Gaussianity or the bounds on the isocurvature contribution to the CMB anisotropies to understand the nature of inflation.

The measurement of Cosmic Ray Electrons from 20 GeV to 1 TeV using the Fermi Large Area Telescope
May 15, 2009 | LASR Conference Room | 12:00 PM
Jonathan F. Ormes, University of Denver

The spectrum of electrons near 1 TeV provides important constraints on models of cosmic ray origin and propagation and has been proposed to indicate a possible signature of dark matter. I will report on the measurement of Cosmic Ray Electrons to 1 TeV using the Fermi Gamma-ray Space Telescope’s Large Area Telescope. In contrast to other measurements to date made on balloons or the shuttle where both systematic and statistical errors can be problematic, these results are based on over 4 M electrons > 20 GeV and are statistically precise. Thus, the measurement is limited by systematic errors. A detailed Monte Carlo simulation of the instrument response to both electrons and protons (and helium), combined with the high statistics, allows the systematic errors to be characterized and understood. The results will be described and compared with the other recently published results from Pamela, ATIC and HESS. The astrophysical implications for cosmic ray propagation, sources, and other interpretations will be discussed.

The Cosmic Microwave Background, Interferometry, and Polarization
May 22, 2009 | LASR Conference Room | 12:00 PM
Jonathan Sievers, CITA

Interferometers have played a major role in observations of the Cosmic Microwave Background. The measurement of fringes rather than total power means that interferometers are resistant to a slew of potential systematics, in particular atmospheric fluctuations larger than the field of view are rejected. They are also well-suited for polarization measurements - because they directly measure the polarized signal, gain fluctuations are relatively unimportant. Their principal drawback has been the high cost of getting large numbers of detectors on the sky. However, recent technological developments have raised the prospects of vastly larger interferometers. We discuss the history and present state of interterferometric measurements of the CMB and present thought on future measurements, particularly of primordial B-mode polarization.

Observational Constraints on Gravitational Wave Recoil Kick Velocities in Supermassive Black Hole Binaries from Radio Galaxies
May 29, 2009 | LASR Conference Room | 12:00 PM
C.C. Teddy Cheung, NASA GSFC

In recent years, general relativity simulations of binary black hole mergers have demonstrated that large 'kicks' due to gravitational wave radiation recoil are possible. An observable manifestation of this phenomena would be a displacement of the resultant active nucleus from its parent host galaxy. We test this interesting possibility with astrometric radio and optical measurements of a large sample of radio galaxies, focusing in particular on the class of restarting sources with so-called 'double-double' and 'X'-shaped morphologies. The unusual morphologies of the restarting sources suggest a relatively recent merger, and such angular offset measurements place useful observational constraints on possible kick velocities resulting from super-massive black hole binary mergers.

New Results on CMB Polarization from BICEP and QUaD
June 5, 2009 | LASR Conference Room | 12:00 PM
Clem Pryke, The University of Chicago

I will start with a brief update on the latest results from QUaD. I will then move on to the BICEP1 instrument, it's calibration and analysis, and present ground breaking new results on B-mode polarization in the crucial few degree angular scale range where the inflationary signal is expected to peak. I will finish by describing the on-going BICEP2/Keck-Array program which will produce still more sensitive results within a few years.

A preview of upcoming results from the South Pole Telescope
October 2, 2009 | LASR Conference Room | 12:00 PM
Tom Crawford, The University of Chicago

The South Pole Telescope (SPT) is a 10-meter, millimeter-wave telescope operating at the Amundsen-Scott South Pole Station. The first camera on the SPT, a ~1000-element, three-color, bolometric receiver, has been operational since 2007 and is currently surveying hundreds of square degrees of the southern sky per year in observing bands centered on 90, 150, and 220 GHz. Analysis of the 2008 SPT data has resulted in several interesting discoveries and new results, which will be made public soon, and which I will give an informal survey of here. These results include the apparent discovery of a new population of star-forming galaxies, measurements of the SZ effect from known clusters out to unprecedented clustercentric radii, the first cosmologically interesting catalog of SZ-selected galaxy clusters, and measurements of high-l CMB power spectrum.

Galaxies in the Young Universe: Metallicity, Kinematics, and Gas Flows
October 9, 2009 | LASR Conference Room | 12:00 PM
Dawn Erb, UCSB

A large fraction of the stars in the universe today formed during the redshift interval 1.5<z<3, when the universe was only about 25% of its current age. However, the quantitative study of galaxies in this redshift range from large spectroscopic samples has only recently become feasible. Such spectra offer a unique opportunity to quantify the physical conditions in these distant galaxies and their interactions with the surrounding intergalactic gas. I will discuss the results of a large near-IR spectroscopic survey of star-forming galaxies at z~2, highlighting the galaxies' kinematics, elemental abundances, and large-scale outflows and inflows of gas.

Testing General Relativity on Cosmological Scales with Weak Gravitational Lensing
October 16, 2009 | LASR Conference Room | 12:00 PM
Ali Vanderveld, Caltech/JPL

Weak gravitational lensing is a powerful probe of modifications of General Relativity on cosmological scales, since such modifications can affect both how matter produces gravitational potential wells and how photons move within these wells. I will discuss alternative theories of gravitation and how we may constrain such theories using weak lensing observables, including those that could be obtained with the balloon-borne High Altitude Lensing Observatory (HALO). I will also discuss the ''parametrized-post-Friedmannian'' approach for obtaining model-independent constraints, in which new parameters are introduced to characterize the departure from General Relativity on large scales.

Signals from the Cosmological Recombination Epoch
October 23, 2009 | LASR Conference Room | 12:00 PM
Jens Chluba, CITA

Very soon the Planck Surveyor will start observing the CMB temperature and polarization anisotropies with unprecedented precision. For the analysis of these data sets it will be very important to understand the ionization history of the Universe at redshift z~1100 with very high accuracy, since otherwise uncertainties in the modelling of the recombination process may lead to significant biases in the deduced values of some cosmological parameters.


In addition to the simple fact that electrons are captured by protons and helium ions also some photons are released during the cosmological recombination process, leading to small distortions in the CMB blackbody spectrum which should still be present today. This recombination radiation carries valuable information about the dynamics of recombination and the underlying cosmological parameters, which until now has not been accessed.


In my talk I will review some of the recent computations in connection with the ionization history of the Universe and the CMB power spectra, showing that neglecting details in the physics of recombination will lead to important biases in the values of n_s and Omega_b. Furthermore, I will try to show that one could learn a lot about cosmological parameter, details in the recombination dynamics, energy release at high redshift and possible dark matter annihilations during recombination by directly measuring the cosmological recombination radiation.

Satellite Galaxies in LambdaCDM: Orbits, Merging & Disruption
October 30, 2009 | LASR Conference Room | 12:00 PM
Andrew Wetzel, UC Berkeley

Dark matter halos that merge with larger halos persist as subhalos, which host satellite galaxies. While subhalos are rapidly stripped of their dark mass, the compact luminous material remains intact longer, making the correspondence of galaxies with severely stripped suhalos unclear. I use a high-resolution, cosmological N-body simulation to explore satellite galaxy merging and tidal disruption. Satellite subhalos must be well-resolved down to ~1% of their mass at infall, and many satellites experience tidal disruption prior to merging with the central galaxy. Using abundance matching to assign stellar mass to subhalos, I compare with observed galaxy clustering, satellite fractions, and cluster luminosity functions. I also explore a simple analytic model based on dynamical friction for satellite infall. Finally, I examine the orbital distribution of infalling satellites and its evolution with halo mass and redshift.

Cosmological hydrogen recombination: the effect of extremely high-n states and forbidden transitions
November 6, 2009 | LASR Conference Room | 12:00 PM
Daniel Grin, California Institute of Technology

Thanks to the ongoing Planck mission, a new window will be opened on the properties of the primordial density field, the cosmological parameters, and the physics of reionization. Much of Planck's new leverage on these quantities will come from temperature measurements at small angular scales and from polarization measurements. These both depend on the details of cosmological hydrogen recombination; use of the CMB as a probe of energies greater than 10^16 GeV compels us to get the ~eV scale atomic physics right.



One question that remains is how high in hydrogen principle quantum number we have to go to make sufficiently accurate predictions for Planck. Using sparse matrix methods to beat computational difficulties, I have modeled the influence of very high (up to and including n=200) excitation states of atomic hydrogen on the recombination history of the primordial plasma, resolving all angular momentum sub-states separately and including, for the first time, the effect of hydrogen quadrupole transitions. I will review the basic physics, explain the resulting plasma properties, discuss recombination histories, and close by discussing the effects on CMB observables.

Probing the Physics of the Beginning: Primordial Non-Gaussianity and Gravitational Waves
November 13, 2009 | LASR Conference Room | 12:00 PM
Amit Yadav, Institute for Advanced Study, Princeton

In the last few decades, advances in observational cosmology have given us a standard model of cosmology. We know the content of the universe to within a few percent. With more ambitious experiments on the way, we hope to move beyond the knowledge of what the universe is made of, to why the universe is the way it is. In my talk, I will focus on what we can expect to learn about the dynamics of the universe at the very earliest moments. I will discuss theoretical predictions from inflationary models and their observational consequences in the cosmic microwave background anisotropies. In particular, I will focus on two observational signatures, primordial non-Gaussianity and gravitational waves, as probes for the physics of the beginning.

Recent Results on Dark Matter Searches with Fermi
November 20, 2009 | LASR Conference Room | 12:00 PM
Simona Murgia, SLAC/KIPAC

The Fermi Large Area Telescope (LAT) has been successfully launched from Cape Canaveral on 11 June 2008. It is exploring the gamma ray sky in the energy range from 20 MeV to over 300 GeV with unprecedented sensitivity. One of the most exciting science questions that the Fermi LAT will address is the nature of dark matter. Several theoretical models have been proposed that predict the existence of Weakly Interacting Massive Particles (WIMPs) that are excellent dark matter candidates. The Fermi LAT investigates the existence of WIMPs indirectly, primarily through their annihilation or decay into photons and into electrons and positrons. I will present recent results on these searches.

New Results for Giant Arc Statistics in ~100 Clusters
December 4, 2009 | LASR Conference Room | 12:00 PM
Assaf Horesh, Tel-Aviv University

Gravitational lensing is frequently used to map the evolution of cluster mass profiles, ellipticities, and substructure. One approach is to perform detailed modeling of individual clusters using strong and weak lensing, but this is generally suited only to deep data for individual clusters that exhibit numerous lensed images, and the results may not be representative of the majority of clusters. A complementary approach is to measure the statistics of lensed arcs in large samples of clusters. Over the past decade, a debate has gone on about the nature of cluster samples selected by different methods, and about whether or not real clusters are highly more efficient producers of arcs than expected from theory. I will present an analysis of the arc statistics in a sample of ~100 galaxy clusters observed with the HST/ACS. X-ray selected clusters are much more efficient lenses than optically-selected clusters of similar optical luminosity, showing that optical selection yields lower-mass, perhaps marginally bound, structures. I will also present our past and in-progress comparison of observed arc statistics with simulations that aim to include all the theoretical and observational aspects of the problem.