Oct 04

"Dynamics of Bubble Collisions - a New Mechanism for Creating Bubbles in the Early Universe"
Lam Hui, Columbia University (TCC Visiting Speaker)

We will discuss the dynamics of bubble collisions, in particular how they can trigger a classical transition into new vacua, creating new bubbles that might have interesting cosmological consequences.

Oct 11

"The Hunt for the First Supernovae"
Jacob Hummel, University of Texas at Austin

One of the most exciting aspects of the upcoming launch of the James Webb Space Telescope (JWST) is the prospect of possibly being able to image the first luminous objects. These stars, the first sources of light in the universe since the Big Bang, ended the dark ages and are at least partially responsible for the reionization of the universe. While the first stars themselves are unlikely to be visible, they are predicted to be very massive and may end their lives as extremely energetic Pair Instability Supernovae (PISNe), releasing up to 10^53 ergs of energy. These explosions are expected to be within the detection limits of the JWST. While the properties of the first stars are fairly well understood, their rates of occurence are not; here we present an improved calculation of the source density and the resulting observability with the goal of developing effective search strategies for detecting these explosions.

Oct 18

"Looking for WIMPs with the Cryogenic Dark Matter Search (CDMS)"
Matt Fritts, University of Minnesota (TCC Visiting Speaker)

The Cryogenic Dark Matter Search (CDMS) seeks Weakly-Interacting Massive Particles (WIMPs), which are thought to comprise 80% of the matter in the universe. We look for rare collisions with nuclei in semiconductor detectors cooled to 40 mK. To establish the necessary low background the experiment operates deep underground, utilizes layers of active and passive shielding, and is designed to distinguish interactions by type and position.

Last December we released our analysis of the final data from the phase known as CDMS-II, which took place in the Soudan Underground Laboratory in northern Minnesota. We observed only 2 events with a WIMP-like signature and placed the strongest upper limit to date on the spin-independent WIMP-nucleon interaction cross-section for WIMP masses greater than 80 GeV/c2. In recent months much interest (and some controversy) has been raised by possible evidence of much lighter (~10 GeV/c2) WIMPs in other direct-detection experiments.

New analyses of data in-hand and upgrades for future phases of CDMS involving detector design modifications, greater target mass, and deeper sites are currently in the works.

Nov 08

"Measuring the Universe: Recent Developments in Baryon Acoustic Oscillations"
Nikhil Padmanabhan, Yale University (TCC Visiting Speaker)

I will discuss using baryon acoustic oscillations as a standard ruler to measure the expansion rate of the Universe, focusing on recent theoretical and observational developments, On the theoretical side, I will discuss developments in a perturbative description of nonlinear effects, as well as techniques to undo these nonlinearities. I will also present initial results from the Baryon Oscillation Spectroscopic Survey, that aims to measure the distance scale at redshifts of 0.3, 0.6, and 2.5. I will conclude with comments on possible future surveys, including the proposed BigBOSS survey.

Nov 22

"Self-regulated Evolution of Galaxies and Supermassive Black Holes"
Joop Schaye, Leiden Observatory (TCC Visiting Speaker)

I will use results from the OverWhelmingly Large Simulations (OWLS) project to investigate the physics driving the growth of galaxies and supermassive black holes. Feedback from star formation and from accretion onto black holes can regulate the growth of low- and high-mass galaxies, respectively. This self-regulation has some counter-intuitive implications. For example, the galaxy star formation rate is insensitive to the star formation law and the mass of the black hole is insensitive to the efficiency of the AGN feedback. I will argue that the masses of supermassive black holes may be controlled by their host dark haloes rather than by their host stellar bulges. I will also argue that gaseous haloes of groups of galaxies are key to understanding the feedback processes relevant for galaxy formation and that these processes may work rather differently than typically assumed. Finally, I will show that baryonic physics affects the matter distribution out to much larger scales than previously thought.