9 January 2009	6 February 2009	6 March 2009
16 January 2009	13 February 2009	13 March 2009
23 January 2009	20 February 2009
30 January 2009	27 February 2009

Kenneth M Nollett, Argonne National Laboratory

A potpourri of lithium problems  

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.

Amir Hajian, Princeton University

Precision Cosmology in the Next Decade: Origin of Cosmic Acceleration from CMB and Large Scale Structure Surveys  

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.

Kathryn Zurek, FNAL

Multi-component dark matter  

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.

Carlos E.M. Wagner, Argonne National Laboratory and Univ. of Chicago

Cosmology and the LHC  

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.

Jarrett L Johnson, The University of Texas at Austin

Star Formation in the Early Universe  

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.

Cyril Pitrou, University of Oslo, Norway

The Non-linear Evolution of the Cosmic Microwave Background  

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.

Stephen E. Healey, Stanford University / KIPAC

An Early Look at the Fermi Blazar Population  

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.

Reinhard Schlickeiser, Ruhr-University Bochum

First-order distributed Fermi acceleration of cosmic ray hadrons in non-uniform magnetic fields  

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.

Jack Singal, KIPAC / Stanford University

The Extragalactic Radio Background  

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.

Tom Abel, KIPAC/Stanford

Structure Formation in the First Billion Years of the Universe  

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.

21 January 2009	18 February 2009	11 March 2009
28 January 2009	25 February 2009

Dan Hooper, Fermilab/U Chicago

Charged Cosmic Rays and Dark Matter  

Recent results from the PAMELA and ATIC experiments have lead us to the conclusion that highly relativistic (10-600 GeV) electrons and positrons are surprisingly ubiquitous in cosmic ray spectrum. Although the source of these unexpected particles is currently not known, an exciting possibility is that they might be the product of dark matter particles annihilating in the local halo of the Milky Way. I will discuss what it would take for dark matter to produce these signals, and the future measurements that will enable us to identify the origin of these particles once and for all.

Stefan Funk, Kavli Institute for Particle Astrophysics and Cosmology, Stanford University

GLAST, HESS and Beyond, Status and Future of Gamma-ray Astronomy  

The field of gamma-ray astronomy has received considerable attention beyond the high-energy astrophysics community in the recent years. This is in part due to the success of Imaging Atmospheric Cherenkov Telescopes such as HESS, MAGIC and VERITAS measuring gamma-rays in the energy regime above 100 GeV. All these new facilities have lifted gamma-ray astronomy in the last few years from an exotic discipline with a handful of detected sources to a solid astronomical discipline. In addition, the recent launch of the Fermi Space Telescope (FST) and its main instrument, the Large Area Telescope (LAT) measuring gamma-rays outside Earth's atmosphere the energy range beyond 100~MeV adds to the attention and excitement. The Fermi-LAT instrument will solidify the field by detecting several thousands of new sources and by bridging the energy spectra of ground-based detected VHE gamma-ray sources to well-studies objects at X-ray energies. In this seminar I will discuss the current status of the field, as well as the potential for future observatories.

Risa Wechsler, KIPAC / Stanford University

Precision Cosmological Constraints from Optically-Selected Clusters  

I will present new constraints on the matter density and clustering amplitude of matter in the Universe,
based on the largest galaxy cluster catalog available to date, the SDSS maxBCG cluster catalog. When combined with CMB data, these data improve the precision of the parameter constraints by a factor of two, with comparable accuracy to the most recent determinations from X-ray clusters. Our analysis is fully self-calibrated in the sense that we do not rely on a priori determinations of the relation between the number of galaxies in a cluster and a cluster's mass. I will discuss how this approach can be extended to the next generation of photometric surveys, focusing on the Dark Energy Survey. I will discuss which aspects of the future survey are most critical, highlighting the role of uncertainties in the mass-observable relation
and the power of well-selected followup observations to improve the dark energy constraints.

Alexander Kusenko, UCLA

Neutrinos and the dark side of the light fermions  

The past decade has been marked by some remarkable discoveries in the neutrino physics: the particles once believed to be massless have turned out to be massive and have shown evidence of lepton family number violation, as well as other interesting phenomena. While this is exciting, the future may hold even more dramatic discoveries, the hints for which begin to appear in astrophysics and cosmology. The observed neutrino masses imply the existence of some yet undiscovered "right-handed" states, which can be very massive and unreachable, but which can also be light enough to constitute the cosmological dark matter and to account for a number of astrophysical phenomena, from supernova asymmetries and the pulsar kicks to the peculiarities in the reionization and formation of the first stars. I will review the recent progress in neutrino physics, as well as the clues that may lead to future discoveries.

Teresa Montaruli, University of Wisconsin - Madison

Recent Results from IceCube  

After two more construction seasons IceCube, the first cubic-kilometer
neutrino telescope, will be completed as initially planned. The instrumentation of this extremely large volume allows to measure neutrinos in the energy range from about 100 GeV up to energies larger than 10^17 eV. IceCube will reach sensitivites well below expected neutrino fluxes from astrophysical sources accelerating hadrons. A ground-based extensive air-shower, IceTop, measuring showers induced by primaries of energy between 10^15 - 10^17 eV, enriches the physics potential of this observatory at the South Pole operating standalone and in coincidence with the deep ice detector.
The current results of IceCube in incomplete configurations and the physics reach of the full detector will be discussed as well as the low energy extension DeepCore and possible high energy extensions.

14 January 2009	11 February 2009
4 February 2009	4 March 2009

Ruth Gregory, Durham University

Braneworld Black Holes  

Braneworlds are a fascinating way of hiding extra dimensions by confining ourselves to live on a brane. One particular model (Randall-Sundrum) has a link to string theory via living in anti de Sitter space. I'll describe how the ads/cft correspondence has been used to claim that a braneworld black hole would tell us how Hawking radiation back reacts on spacetime, thus solving one of the outstanding problems of quantum gravity - the ultimate fate of an evaporating black hole. I'll review evidence for this conjecture, ending with some recent work that shows it may be problematic.

Phil Kronberg, Los Alamos Laboratory

Expectations, and Probes of Intergalactic Magnetic Fields  

It is likely that intergalactic magnetic fields are naturally seeded by (1) “normal” stellar processes in galaxies, and (2) by central galactic black holes. There may also be (3) a primordial component from the pre-galactic Universe, but this is probably overwhelmed by the first two processes except possibly in cosmic voids. I discuss some methods for probing intergalactic fields, and some recent results. Some are new and tentative, and serve to focus on what better data of the same kinds could be obtained with present instruments. I present a brief overview of what we know about galactic and extragalactic magnetic fields from the local universe from “here” up to z ~ 3. This includes some global a priori calculations of IGM field strengths based on known facts of galactic magnetic energy outflows. I briefly include ideas on of where some distributed UHECR acceleration sites may be found.

Enrico Ramirez, University of California, Santa Cruz

Atypical Thermonuclear Supernovae from Tidally Crushed White Dwarfs  

Suggestive evidence has accumulated that intermediate mass black holes (IMBH) exist in dwarf galactic nuclei and some globular clusters. As stars diffuse in the cluster, some will inevitable wander sufficiently close to the hole that they suffer tidal disruption. An attractive feature of the IMBH hypothesis is its potential to disrupt not only solar-type stars but also compact white dwarf stars. Attention is given to the fate of white dwarfs that approach the hole close enough to be disrupted and compressed to such extent that explosive nuclear burning may be triggered. Consistent modeling of the gas dynamics together with the nuclear reactions allows for a realistic determination of the explosive energy release. Although the explosion will increase the mass fraction escaping on hyperbolic orbits, a good fraction of the debris remains to be swallowed by the hole, causing a bright soft X-ray flare lasting for about a year. Such transient signatures, if detected, would be a compelling testimony for the presence of a moderately mass black hole.

James Beatty, Ohio State University

Ice Fishing for Cosmic Neutrinos  

Cosmic rays at GZK energies produce neutrinos as a consequence of their interactions with the cosmic microwave background radiation. When these neutrinos interact in the Antarctic ice sheet, the resulting showers produce coherent Cherenkov radiation at radio frequencies via the Askaryan mechanism. A balloon instrument, the Antarctic Impulsive transient Antenna (ANITA), has flown over Antarctica twice, most recently during the past austral summer. Results from the first flight and information about the second flight will be presented.

17 March 2009

20 March 2009

Jonathan C. Tan, University of Florida

Massive Star Formation Through The Universe  

I will review three questions in massive star formation research: (1) What was the mass of the first Population III stars? (2) How do present-day massive stars form? (3) What physical processes control the rate at which disk galaxies turn gas into stars?

Marcel Zemp, The University of Michigan

How to Solve a Billion Body Problem? - Insights from High Resolution N-body Simulation into the Structure of Dark Matter Haloes  

I'll talk about recent results and insights we received from two N-body simulation projects: Via Lactea & GHALO. First, I'll present the challenges that such problems pose for even the most powerful supercomputers today and some solutions we came up with in order to optimize our method. In the second part, I'll focus on our findings about the structure of dark matter in haloes and discuss the wealth of structure (like streams, several generations of subhaloes and voids) that are only present in such high resolution simulations.