Cosmology & Gravitation

This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.

Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

 

Tuesday Feb 22, 2011
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We show that, in a model of modified gravity based on the spectral action functional, there is a nontrivial coupling between cosmic topology and inflation, in the sense that the shape of the possible slow-roll inflation potentials obtained in the model from the nonperturbative form of the spectral action are sensitive not only to the geometry (flat or positively curved) of the universe, but also to the different possible non-simply connected topologies.

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Thursday Feb 17, 2011
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For nearly the past century, the nature of dark matter in the Universe has puzzled astronomers and physicists. During the next decade, experiments will determine if a substantial amount of the dark matter is in the form of non-baryonic, Weakly-Interacting Massive Particles (WIMPs). In this talk I will discuss and interpret modern limits on WIMP dark matter from a variety of complementary methods. I will show that we are just now obtaining sensitivity to probe the parameter space of cosmologically-predicted WIMPs created during the earliest epoch in the Universe.

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Wednesday Feb 16, 2011

The availability of high precision observational data in cosmology means that it is possible to go beyond simple descriptions of cosmic inflation in which the expansion is driven by a single scalar field. One set of models of particular interest involve the Dirac-Born-Infeld (DBI) action, arising in string cosmology, in which the dynamics of the field are affected by a speed limit in a manner akin to special relativity. In this talk, I will introduce a scalar-tensor theory in which the matter component is a field with a DBI action.

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Thursday Feb 03, 2011
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While understanding the evolution of galaxies is one of the major themes of
contemporary astronomy, most empirical studies focus only on the evolution
of distribution functions (e.g., the luminosity function), effectively
treating galaxies in isolation. The new generation of large imaging and

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Tuesday Feb 01, 2011
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I will discuss a powerful way to examine the nature of dark energy using a measurement of the growth of galaxy clusters over cosmic time. A novel technique that uses the Cosmic Microwave Background as a backlight allows the detection of galaxy clusters out to the time of their first formation. Using this technique, I will present the first constraints on cosmological parameters obtained with the Atacama Cosmology Telescope, as well as exciting prospects for the future.

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Monday Jan 31, 2011
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Black holes are associated with a variety of the most extreme and counter-intuitive phenomena in astronomy and physics. However, despite the passage of nearly 40 years since the discovery of the first strong black hole candidate, we have scant evidence that general relativity provides an accurate description of gravity in the immediate vicinity of astrophysical black holes. Over the next few years this will change dramatically.

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Tuesday Jan 25, 2011
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In the picture of eternal inflation, our observable universe resides inside a single bubble nucleated from an inflating false vacuum. Some of the theories giving rise to eternal inflation predict that we have causal access to collisions with other bubble universes, providing an opportunity to confront these theories with observation. In this talk, I will outline progress on the theoretical description of eternal inflation and bubble collisions, and present results from the first search for the effects of bubble collisions in the WMAP 7-year data.

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Thursday Dec 09, 2010
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Theories with extra dimensions naturally give rise to a large landscape of vacua stabilized by flux. I will show that the fastest decay is a giant leap to a wildly distant minimum, in which many different fluxes discharge at once. Indeed, the fastest decay is frequently the giantest leap of all, where all the fluxes discharge at once, which destabilizes the extra dimensions and begets a bubble of nothing. Finally, I will discuss how these giant leaps are mediated by the nucleation of "monkey branes" that wrap the extra dimensions.

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Tuesday Nov 30, 2010
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Five decades ago, Aharonov and Bohm illustrated the indispensable role of the vector potential in quantum dynamics by showing (theoretically) that scattering electrons around a solenoid, no matter how thin, would give rise to a non-trivial cross section that had a periodic dependence on the product of charge and total magnetic flux. (This periodic dependence is due to the topological nature of the

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Tuesday Nov 09, 2010
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I will discuss the emergence of large, localized, pseudo-stable configurations (oscillons) from inflaton fragmentation at the end of inflation. Remarkably, the emergent oscillons take up >50 per cent of the energy density of the inflaton. First, I will give an overview of oscillons, provide some analytic solutions and discuss their stability. Then, I will discuss the conditions necessary for their emergence and provide estimates for their cosmological number density. I will show results from detailed 3+1-dimensional numerical simulations and compare them to the analytic estimates.

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