College of Arts and Sciences

Understanding the very early universe is linked inextricably with understanding the resolution of cosmological singularities. I will discuss “string gas cosmology”, one of the approaches making use of string theory to obtain an improved picture of the early universe cosmology. In particular, I will show that string gas cosmology can lead to a new structure formation scenario in which string thermodynamic fluctuations generate a scale-invariant spectrum of adiabatic fluctuations.

Continue reading… String Gas Cosmology and Structure Formation – Robert Brandenberger

I will discuss at a colloquium level the robust model independent predictions of inflation and compare these predictions with the results of the observations of the fluctuations of the cosmic mictrowave background radiation.

Continue reading… The Origin of the Big Bang: the status of inflation after WMAP – Slava Mukhanov

In a few years, after Fermilab’s Tevatron turns off and initial LHC results are available, the High Energy Physics community will be at a crossroads: what type of facility to consider next? Neither proton nor electron machines hold much prospect for advancing the energy frontier beyond the LHC. But recent innovations in manipulating muon beams make it possible to imagine a third type of facility for HEP: a muon collider. An energy frontier muon collider could potentially fit on the Fermilab site, opening a completely new window into fundamental particle processes. In addition to presenting the basic concept, this talk will discuss the challenges inherent in creating,

Continue reading… Prospects for a New Type of High Energy Physics Facility: a Muon Collider – Tom Roberts

We are at the brink of a Golden Age of Astrophysics with the promise of answers to many long-outstanding questions, including: What is the nature of Dark Matter? What source powers Active Galactic Nuclei? Where do Gamma-Ray Bursts come from? Where do the highest energy Cosmic Rays come from? With an unprecedented number of experiments both active and coming online, there is a real hope that many of these questions may be answered in the near future. I have been lucky enough to be associated with some of the world’s most advanced astrophysical experiments. In this talk, I plan on detailing my life as an experimentalist and how my work has touched on some of these intriguing questions.

Continue reading… Ongoing Mysteries in Astrophysics – Don Driscoll

TBA

Continue reading… Probability in cosmology: from Bayes theorem to the anthropic principle – Roberto Trotta

I present a balloon-borne cosmic microwave background (CMB) polarization experiment, E and B experiment(EBEX). EBEX is designed, i) to detect or set an upper limit (T/S less than 0.03) on the inflationary gravity-wave background polarization anisotropy signal (primordial B-mode), ii) to measure the CMB polarization anisotropy signal induced by gravitational lensing (lensing B-mode), and iii) to measure galactic dust emission (120 GHz – 450 GHz) in order to monitor foreground contamination. In this talk, I present the EBEX science goals as well as an instrument overview. In particular among a number of subsystems in EBEX, I discuss a half-wave plate polarimeter using a superconducting magnetic bearing.

Continue reading… EBEX, a CMB B-mode polarization experiment – Tomotake Matsumura

Host: NOTE: The event is free, but registration is required, at www.case.edu/events/dls/register.html

Continue reading… Warped Passages: Unravelling the Mysteries of the Universe’s Hidden Dimensions

The present-day acceleration of the Universe is one of the greatest mysteries of modern cosmology. In the framework of general relativity, the expansion could be caused by either a “cosmological constant”, or a dynamical dark energy component (DDE). In this talk I will describe a novel theoretical approach to distinguishing between these two possibilities, namely, via the clustering properties of DDE. By following the dynamical evolution of matter perturbations in a cosmic mix of matter and DDE, we find the very interesting result that the DDE tends to form voids in the vicinity of gravitationally collapsing matter. I will discuss these voids in detail,

Continue reading… Voids of Dark Energy – Sourish Dutta

Even in what has been termed an age of `precision cosmology’ certain anomalies on a range of astrophysical scales are observed and demand the existence of unseen types of matter or modifications to our current gravitational theory. In this article the issue of the nature of the mysterious `dark energy’ has been explored in a model-independent way. A maximum-entropy technique is developed and used to reconstruct the equation of state of dark energy within a bayesian framework. The motivation for the use of the MaxEnt technique is the lack of good data points in comparison to the number of parameters required for a sufficient characterization of dark energy.

Continue reading… Reconstructing dark energy using Maximum Entropy – Caroline Zunckel

The properties of the primordial perturbations seeded during a stage of inflation are determined by the quantum state of the inflaton. This state is usually assumed to be the “vacuum”, since one expects excited states to decay into the state of lowest energy. In the talk I discuss whether this assumption holds in the presence of a short-distance cut-off. I describe the calculation of transition probabilities between excited states and the vacuum, and discuss the implications of the results that I obtain.

Continue reading… Do quantum excitations of the inflaton decay? – Cristian Armendariz-Picon

I discuss gravitational wave experimental signatures (bursts and stochastic background) of cosmic strings. I will show burst rates that are substantially lower (about a factor of 1000) than previous estimates suggest and explain the disagreement. Initial LIGO is unlikely to detect bursts from field theoretic cosmic strings, though it may detect cosmic superstring bursts. I also compare the stochastic background produced by a network of strings with a wide range of experiments and indirect bounds. If the latest cosmic string simulation results are correct then a large area of superstring parameter space is ruled out by pulsar timing observations.

Continue reading… Cosmic (super)strings: Gravitational wave bursts, stochastic background, and experimental constraints – Xavier Siemens

Cosmology ultimately aims to explain the initial conditions at the beginning of time and the entire subsequent evolution of the universe. The “beginning of time” can be understood in the Wheeler-DeWitt approach to quantum gravity, where homogeneous universes are described by a Schroedinger equation with a potential barrier. Quantum tunneling through the barrier is interpreted as a spontaneous creation of a small (Planck-size) closed universe, which then enters the regime of cosmological inflation and reaches an extremely large size. After sufficient growth, the universe can be adequately described as a classical spacetime with quantum matter. The initial quantum state of matter in the created universe can be determined by solving the Schroedinger equation with appropriate boundary conditions.

Continue reading… Quantum cosmology and the conditions at birth of the universe – Serge Winitzki

The concordance cosmological model predicts that structures in the Universe form via hierarchical merging, beginning with the smallest dark matter mini-halos. The mass of the smallest halo is set by the initial thermal motion of dark matter particles. After merging into larger systems and subsequent dynamical evolution, most halos lose between 50% and 99% of their mass but an interesting fraction of dark matter remains in self-bound clumps at all mass scales. The smallest substructure has important implications for the detection of dark matter annihilation, predicted by SUSY models.

Continue reading… The life and death of dark matter halos: predictions for neutralino annihilation

Hints from quantum gravity suggest the existence of a preferred frame. One way to accommodate such a frame in general relativity without sacrificing general covariance is to couple the metric to a dynamical, timelike, unit-norm vector field–the “aether”. I will discuss observational constraints on a class of such theories, with a focus on post-Newtonian effects and radiation from binary pulsar systems, and show that a subset remains viable.

Continue reading… Aethereal Gravity – Brendan Foster

We reconstruct the potential of a quintessence field from current observational data, including new supernova data, plus information from the cosmic microwave background and from baryon acoustic oscillations. We model the potential using Pade approximant expansions as well as Taylor series, and use observations to assess the viability of the tracker hypothesis. Present data provide some insights into the shape of a presumptive quintessence potential, but also strengthen the model selection preference for the cosmological constant over evolving models. They also show some signs, though inconclusive, of favouring tracker models over non-tracker models under our assumptions.

Continue reading… The Quintessence Potential: Need for Features and Tracking? – Martin Sahlen

One of the great mysteries of modern cosmology is the origin and nature of dark energy – a smooth component that contributes about 70% of the total energy density in the universe and causes its accelerated expansion. Here I present results from a comprehensive study of a class of dark energy models, exploring their dynamical behavior using the method of flow equations and the Monte Carlo Markov Chain machinery that have previously been applied to inflationary models. I comment on the current and expected future constraints, insights into the dynamics of dark energy, figures of merit, and a classification of theoretical models.

Continue reading… Exploring the Dark Energy Domain – Dragan Huterer

TBA

Continue reading… Probing Dark Energy – Josh Frieman

We use the full quantum treatment to study formation of a black hole as seen by an asymptotic observer. Using the Wheeler-de Witt equation to describe a collapsing shell of matter (a spherical domain wall), we show that the black hole takes an infinite time to form in the quantum theory, just as in the classical treatment. Asymptotic observers will therefore see a compact object but never see effects associated with an event horizon. To explore what signals such an observer would see we study radiation of quantum fields in this background using two approaches: functional Schroedinger method and an adaptation of Hawking’s original calculation.

Continue reading… Black Hole Formation, Evaporation and the Information Loss Problem – Dejan Stojkovic

Cross section measurements for quiescent stellar burning are hampered mainly by extremely low counting rate and cosmic background. Some of the main reactions of H-burning phase have been measured at the LUNA facility (Laboratory for Underground Nuclear Astrophysics) taking advantage of the very low background environment of the Underground Gran Sasso National Laboratory in Italy. The adopted experimental techniques will be presented together with the latest results on the 14N(p,g)15O reaction and the status of the ongoing 3He(4He,g)7Be experiment. Furthermore a brief overview of the ALNA (Accelerator Laboratory for Nuclear Astrophysics underground) project, as a part of the new future Underground DUSEL laboratory in the USA,

Continue reading… Nuclear astrophysics underground – Heide Costantini

Neutrinoless double beta decay has recently become a top priority for the global experimental neutrino physics program. Double beta decay has the potential to resolve the scale of the neutrino mass spectrum, and is also the only practical tool we have for understanding the particle/anti- particle nature of the neutrino. The Enriched Xenon Observatory (EXO) collaboration is developing sensitive searches for the double beta decay of Xenon-136. Our first experiment, EXO-200, will be the largest double beta decay experiment ever attempted by an order-of-magnitude, and is rapidly being constructed. We are also pursuing R and D to realize a system to tag the daughter barium nucleus of the decay using the techniques of single-ion spectroscopy.

Continue reading… Searching for double beta decay with the Enriched Xenon Observatory – Carter Hall

The bulge of our Galaxy is illuminated by the 0.511 MeV gamma-ray line flux from annihilations of nonrelativistic positrons. The emission is strongly concentrated at the Galactic Center, in contrast to gamma-ray maps tracing nucleosynthesis (e.g., the 1.809 MeV line from decaying ^26Al) or cosmic ray processes (e.g., the 1-30 MeV continuum), which reveal a bright disk with a much less prominent central region. Central to resolving the origin of the positrons is the question of their injection energies, which range up to 100 MeV or even higher in recent astrophysical and exotic (requiring new particle physics) models. If positrons are generated at relativistic energies,

Continue reading… Positron annihilations at the Galactic Center: Generating more questions than answers – Hasan Yuksel