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 Sep 29, 2015
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In order for quantum fluctuations during inflation to be converted to classical stochastic perturbations, they must couple to an environment which produces decoherence. Gravity introduces inevitable nonlinearities or mode couplings. We study their contribution to quantum-to-classical behavior during inflation. Working in the Schrodinger picture, we evolve the wavefunctional for scalar fluctuations, accounting for minimal gravitational nonlinearities. The reduced density matrix for a given mode is then found by integrating out shorter-scale modes.

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Tuesday Sep 22, 2015
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I describe an inflation model that can generate a cosmological magnetic seed field of nG strength on Mpc length scales today that could explain observed few microG large-scale galactic magnetic fields. I also summarize some of the extensions of this model that have been developed over the last two decades, as well as open questions about such models.

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Tuesday Sep 15, 2015
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The Lagrangian dynamics of a fluid element within a self-gravitational matter field is intrinsically nonlocal due to the presence of the tidal force. Instead of searching for local approximations, we provide a statistical solution that could decouple the evolution of the fluid parcel from the surrounding environment. Given the probability distribution of the matter field, the method produces a set of ordinary differential equations to be solved locally.

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Tuesday Sep 08, 2015
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In this talk I’ll discuss an exotic theory of gravity known as “partially massless” gravity. The linear partially massless theory displays many features analogous to those of electromagnetism, including an electric/magnetic duality. However, the structure of gauge charges is much richer than in E&M. I’ll present the analogues of electric point charges and Dirac monopoles.

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Tuesday Jul 21, 2015

Current and near-future cosmological surveys can provide powerful tests of gravity on the largest scales. However, in order to extract this information, it is essential to understand the host of parameter degeneracies which may arise. I present two approaches towards this goal, with a focus on the use of weak gravitational lensing measurements in combination with other probes. First, I discuss a novel expression for a weak lensing power spectrum under alternative theories of gravity.

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Thursday Jul 16, 2015
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On small scales, our understanding of dark matter in galaxies is incomplete. One example is that high resolution simulations predict a large number of subhalos in dark matter halos, which should be seen in our Milky Way galaxy as a host of satellite galaxies. Many plausible astrophysical mechanisms have been proposed to explain why we don't clearly see large numbers of such satellite galaxies, but this remains a test of the cold dark matter scenario that has yet to be passed.

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Tuesday Jul 14, 2015
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Eugenio Bianchi and Matteo Smerlak have found a beautiful relationship between the Hawking radiation energy and von Neumann entropy in a conformal field emitted by a semiclassical two-dimensional black hole. Shohreh Abdolrahimi and I compared this relationship with what might be expected for unitary evolution of a quantum black hole in four and higher dimensions.

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Tuesday Jun 02, 2015
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I will present a novel approach to explain the smoothness and flatness of the universe on large scales and the generation of a nearly scale-invariant spectrum of adiabatic density perturbations.

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Tuesday Apr 28, 2015
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High resolution CMB experiments, such as ACT, SPT, and the Planck satellite are making precision measurements of the secondary anisotropies caused by the thermal Sunyaev Zel'dovich (tSZ) effect from galaxy clusters. However, our ability to obtain cosmological information from this tSZ signal is limited by our theoretical understanding of the baryons in clusters and groups.

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