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.

 

Thursday Dec 12, 2013

We study the dynamics of a 2+1 dimensional relativistic viscous conformal fluid in Minkowski spacetime. Such fluid solutions arise as duals, under the "gravity/fluid correspondence", to 3+1 dimensional asymptotically anti-de Sitter (AAdS) black brane solutions to the Einstein equation. We examine stability properties of shear flows, which correspond to hydrodynamic quasinormal modes of the black brane. We find that, for sufficiently high Reynolds number, the solution undergoes an inverse turbulent cascade to long wavelength modes.

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Tuesday Dec 10, 2013
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Recently there has been a successful non-linear covariant ghost-free generalization of Fierz-Pauli massive gravity theory, the dRGT theory. I will explore the cosmology in the decoupling limit of this theory. Furthermore, I will construct a Proxy theory to dRGT from the decoupling limit and study the cosmology there as well and compare the results. Finally, I will discuss the quantum consistency of the theory.

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Tuesday Dec 10, 2013
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TBA

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Thursday Dec 05, 2013
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Within the Minimal Supersymmetric Standard Model (MSSM), LHC bounds suggest that scalar superpartner masses are far above the electroweak scale. Given a high superpartner mass, nonthermal dark matter is a viable alternative to WIMP dark matter generated via freezeout. In the presence of moduli fields nonthermal dark matter production is associated with a long matter dominated phase, modifying the spectral index and primordial tensor amplitude relative to those in a thermalized primordial universe.

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Tuesday Dec 03, 2013
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There is good evidence that the universe underwent an epoch of accelerated expansion sometime in its very early history, and that it is entering a similar phase now. This talk is in two parts. The first part describes what I believe to be the take-home message about inflationary models, coming both from the recent Planck results and from attempts to embed inflation within a UV completion (string theory). I will argue that both point to a particularly interesting class of inflationary models that also evade many of the tuning problems of inflation.

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Tuesday Nov 26, 2013
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I will present Cosmological FRW Solutions in BiGravity Theories and discuss their stability. After deriving the stability bound, one realizes that in Bigravity (in contradistinction to the FRW massive gravity case) the tension between requirements stemming from stability and those set by observations is resolved. The stability bound can also be derived in the decoupling limit of Bigravity. In this context an intriguing duality between Galilean interactions has emerged.

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Friday Nov 15, 2013
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After multiple high precision detections (ACT, SPT, Planck) gravitational lensing has become a new source of relevant cosmological information: combining it with other probes (e.g. the large scale structure) can give significant insight on the evolution of the Dark Energy component. Developing new algorithms of estimate of this signal will allow the community to exploit this observable as a new and independent probe in cosmology.

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Tuesday Nov 12, 2013
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It has been suggested that recent cosmological and
flavor-oscillation data favor the existence of additional neutrino species
beyond the three standard flavors. We apply Bayesian model selection to
determine whether there is any evidence from current cosmological datasets for
the standard cosmological model to be extended to include additional neutrino
flavors. The datasets employed include cosmic microwave background temperature,
polarization and lensing data, and measurements of the baryon acoustic

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Monday Nov 11, 2013
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Galaxy clusters form from the rarest peaks in the initial matter distribution, and hence are a sensitive probe of the amplitude of density fluctuations (sigma_8), the amount of matter in the universe, and the growth rate of structure. Galaxy clusters have the potential to constrain dark energy and neutrino masses. However, cluster cosmology is currently limited by systematic uncertainties due to poorly understood intracluster gas physics.

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Tuesday Nov 05, 2013

A central problem in
galaxy formation is to understand why star formation is so inefficient. Within
individual galaxies, gas is converted into stars at a rate two orders of
magnitude slower than unimpeded gravitational collapse predicts, a fact
embodied in the low normalization of the observed Kennicutt-Schmidt (K-S)
relationship between star formation rate surface density and gas surface
density. Star formation in galaxies is also globally inefficient in the sense

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