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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.

 

Mardi mai 15, 2012
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In this talk I provide a model where the late time acceleration of the universe emerges from a BCS-like condensation of sterile neutrinos. This scenario can be naturally accommodated by general relativity covariantly coupled to sterile neutrinos, where the neutrinos act like an "aether" field.  We show that when active neutrinos couple to the neutrino condensate, they oscillate at a rate proportional to the dark energy density.  As a result, the oscillation of neutrinos and dark energy are tied in with the same mechanism.

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Mardi mai 08, 2012
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With the emergence of the dark sector in cosmology,  a variety of modified theories of gravity have come to the fore. I will discuss a framework which can be used to test gravity on large scales and the observational programmes that might lead to the tightest constraints.

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Jeudi mai 03, 2012
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I will discuss string cosmology and the dynamics of multiple scalar fields in potentials that can become negative, and their features as (Early) Dark Energy models. The point of departure is the ``String Axiverse'', a scenario that motivates the existence of cosmologically light axion fields as a generic consequence of string theory. These fields can constitute part of the Dark Matter, suppressing structure formation in a manner similar to massive neutrinos. Future observations will constrain their existence to percent level accuracy.

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Mardi mai 01, 2012
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We review the notion of a quantum state of the universe and its role in fundamental cosmology. Then we discuss recent work which points towards a profound connection, at the level of the quantum state, between (asymptotic) Euclidean AdS spaces and Lorentzian de Sitter spaces. This gives a new framework in which (a mild generalization of) AdS/CFT can be applied to inflationary cosmology.

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Lundi avr 30, 2012
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I will describe the tight connection between cosmic baryon number and cosmic magnetic fields, and also some recent work on chiral magnetic effects in cosmology.

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Mardi avr 24, 2012
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The curvaton scenario provides a simple explanation for the generation of the cosmological perturbations, however most works have focused on cases with rather trivial curvaton energy potentials, e.g. quadratic ones. In this talk I will present the rich phenomenology of curvatons by showing that non-quadratic curvatons exhibit new behaviors, leading to interesting signals in the resulting density perturbations. A string theory realization of the curvaton scenario will also be discussed, where D-branes located in a warped throat region of the internal space play the role of curvatons.

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Mardi avr 17, 2012
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In this talk I will present evidence that accounting for the presence of hierarchies in string compactifications naturally leads to a UV sensitivity of dark matter in contrast to what is usually assumed. In particular, we will see that the existence of cosmological moduli may lead to a non-thermal history for the early universe and modifications in the primordial production of dark matter.

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Mardi avr 10, 2012
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Dwarf galaxies are the most know dark matter dominated luminous objects in Universe. Observing the line of sight velocity and position of stars in Milky way satellites, and assuming the dark matter potential and a specific configuration of stellar orbits, one can obtain the mass profile of dark matter in galaxies.

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Mardi mar 20, 2012
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Over
the past several decades we have obtained increasingly precise data on the
distribution of galaxies in the Universe and on the distribution of primordial
perturbations via CMB measurements.  This trend is likely to continue for
the foreseeable future.  In this talk I will discuss some new things to do
with data from the CMB, galaxy surveys, and future 21-cm surveys look for new
physics in the early and late Universe.  Topics will include cosmic
birefringence, new tests for parity violation, gravitational lensing,

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Lundi mar 19, 2012
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I will discuss a wide class of models which realise a bounce in a spatially flat Friedmann universe in standard General Relativity. The key ingredient is a noncanonical, minimally coupled scalar field
belonging to the class of theories with Kinetic Gravity Braiding/Galileon-like self-couplings. In these models, the universe smoothly volves from contraction to expansion, suffering neither from ghosts
nor gradient instabilities around the turning point. The end-point of he evolution can be a standard radiation-domination era or an nflationary phase.

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