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 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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Tuesday Oct 30, 2007
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The detection of primordial non-Gaussianity could provide a powerful means to rule out various inflationary scenarios. Although scale-invariant non-Gaussianity is currently best constrained by the Cosmic Microwave Background, single-field inflation models with changing sound speed can have strongly scale dependent non-Gaussianity. I will discuss the theoretical motivation for such models and present work on the likely ability of current and future large scale structure measurements to constrain them.

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Tuesday Oct 02, 2007

f(R) theories are an alternative approach at the phenomenon of cosmic acceleration, in which the Einstein-Hilbert action for gravity is modified by adding a function of the Ricci scalar, f(R). While at the background level viable f(R) models must closely mimic LCDM, the difference in their prediction for the growth of large scale structures can be sufficiently large to leave detectable signatures in future surveys. In this talk, after reviewing the conditions for the background viability of f(R) theories, I will focus on scalar perturbations.

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Tuesday Sep 18, 2007
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The non-Gaussianity of the primordial cosmological perturbations will be strongly constrained by future observations like Planck. It will provide us with important information about the early universe and will be used to discriminate among models. I will review how different models of the early universe can generate different amount and shapes of non-Gaussianity.

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Tuesday Aug 21, 2007
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The Origin of the Large Scale Structure is one of the key issue in Cosmology.
A plausible assumption is that structures grow via gravitational amplification
and collapse of density fluctuations that are small at early times.
The growth history of cosmological fluctuations is a fundamental observable
which helps in hunting for evidences of new physics, currently missing from our picture
of the universe, but potentially crucial to explain its past, present and future history.
I'll show how we investigated if the gradual growth of structures observed

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Tuesday May 01, 2007
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We introduce a framework that allows to calculate cosmological perturbations in a gauge invariant manner to any order. The two main features of this framework are to take physical observables as basic objects and to treat the variables describing the background geometry as fully dynamical. Backreaction effects can therefore naturally adressed. At the end I will mention applications to Loop Quantum Cosmology.

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Tuesday Apr 24, 2007
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Dark matter and dark energy can be explained without resorting to exotic fields if one accepts that the geometry of spacetime is governed by suitable generalized gravitational theories based on Lagrangians that are non-linear in the curvature of a metric and/or a torsionless linear connection, i.e. in second order and first order formalisms.

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Tuesday Apr 17, 2007
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We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit.

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