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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 déc 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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Mardi 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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Vendredi 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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Mardi nov 12, 2013
Speaker(s): 

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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Lundi 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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Mardi 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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Jeudi oct 31, 2013
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In this talk I will give an
introduction to some of my research into modified gravity over the last three
years. I will begin by describing my implementation of chameleon models into
supersymmetry and discuss some of the new features and cosmology that arise
in this formalism. I will then change direction and talk about my work
using astrophysical effects as novel probes of modified gravity theories
and present some new results on modified gravity stellar oscillation theory.

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Mardi oct 29, 2013
Speaker(s): 

Measurements
of gravitational lensing in the Cosmic Microwave Background (CMB)
directly probe the projected distribution of dark matter out to high
redshifts. The CMB lensing maps thus encode a wealth of information about both
fundamental physics (e.g., dark energy and neutrino properties) and
high-redshift astrophysics. I will illustrate this by first reviewing
measurements of CMB lensing with the Atacama Cosmology Telescope, discussing
both CMB lensing auto-correlations and cross-correlations with quasars,

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Mardi oct 22, 2013
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We
will explore the role that conformal symmetries may play in cosmology. First,
we will discuss  the symmetries underlying the statistics of the
primordial perturbations which seeded the temperature anisotropies of the
Cosmic Microwave Background. I will show how symmetry considerations lead us to
three broad classes of theories to explain these perturbations: single-field
inflation, multi-field inflation, and the conformal mechanism. We will discuss
the symmetries in each case and derive their model-independent consequences.

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Mardi oct 15, 2013

Loop quantum
cosmology (LQC) proposes a quantization for homogeneous cosmologies which
success in solving the classical singularity problem. Realistic scenarios call
for the consideration of inhomogeneities. Focusing on the simplest inhomogenous
cosmological model, the Gowdy model with three-torus spatial topology
and linearly polarized gravitational waves, I'll describe an approach to treat
inhomogeneities in the framework of loop quantum cosmology. This is a hybrid

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