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 26, 2008
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Cosmological observations will soon distinguish between the standard slow roll inflationary paradigm and some of its recently developed alternatives. Driven by developments in string theory, many new models include features such as non-minimal kinetic terms, leading to large non-gaussianities, making them observationally testable in the CMB. Models of slow roll inflation can also give rise to large non- gaussianities if the initial inflationary state was sufficiently excited, with a shape dependence that will be clearly distinguishable.

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Tuesday Feb 19, 2008
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The consequences of a modified gravity (MOG) are explored.

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Tuesday Feb 12, 2008
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I\'ll introduce a particular class of fundamental string configurations in the form of closed loops stabilized by internal dynamics. I\\\'ll describe their classical treatment and embedding in models of string cosmology. I\\\'ll present the quantum version and the semiclassical limit that provides a microscopic description of dipole black rings. I\\\'ll show the parametric matching between the degeneracy of microstates and the entropy of the supergravity solution.

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Friday Jan 25, 2008
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The history of human knowledge is often highlighted by our efforts to explore beyond our apparent horizon. In this talk, I will describe how this challenge has now evolved into our quest to understand the physics at/beyond the cosmological horizon, some twenty orders of magnitude above Columbus’s original goal.

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Tuesday Jan 22, 2008
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We consider a consistent construction of the supersymmetric action for a codimension-two brane in six-dimensional Salam-Sezgin supergravity. When the brane carries a tension, we supersymmetrize the brane tension action by introducing a localized Fayet-Iliopoulos term on the brane and modifying the bulk SUSY transformations.
As a result, we find that among the axisymmetric vacua of the system, the unwarped background with football-shaped extra dimensions respects N=1 supersymmetry. We extend the analysis to include the brane multiplets with the couplings to the bulk fields.

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Tuesday Dec 04, 2007
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Linear cosmological perturbation theory is pivotal to a theoretical understanding of current cosmological experimental data provided e.g. by cosmic microwave anisotropy probes. A key issue in this theory is to extract the gauge invariant degrees of freedom which allow unambiguous comparison between theory and experiment. In this talk we will present a manifeslty gauge invariant formulation of general relativistic perturbation theory.

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Tuesday Nov 20, 2007
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We have two strong reasons to argue that Einstein\'s theory of general relativity may be incomplete. First, given that it cannot be expressed within a consistent quantum field theory there is reason to expect higher energy corrections. Second, the observation that we are undergoing a current epoch of accelerated expansion might indicate that our understanding of gravity breaks down at the largest scales.

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Tuesday Nov 06, 2007
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I will discuss a new method of inflaton potential reconstruction that combines the flow formalism, which is a stochastic method of inflationary model generation, with an exact numerical calculation of the mode equations of quantum fluctuations. This technique allows one to explore regions of the inflationary parameter space yielding spectra that are not well parameterized as power-laws. We use this method to generate an ensemble of generalized spectral shapes that provide equally good fits to current CMB and LSS as data as do simpler power-law spectra.

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