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Cosmology & Gravitation

This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.

Seminar Series Events/Videos

TBA
mar 31 2015 - 11:00am
Room #: 400
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TBA
avr 7 2015 - 11:00am
Room #: 400
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avr 13 2015 - 11:00am
Room #: 400
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TBA
avr 14 2015 - 11:00am
Room #: 400
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avr 21 2015 - 11:00am
Room #: 400
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TBA
avr 28 2015 - 11:00am
Room #: 400
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TBA
mai 26 2015 - 11:00am
Room #: 400
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Mardi mar 10, 2015
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Visible matter consists mostly of hydrogen and helium, only a small fraction

of which is in stars. Until recently, the bulk of the gas in the local

universe was in fact not seen. In the largest structures, massive galaxy

clusters, the gas is seen via its x-ray emission, but in the much more

numerous groups and isolated galaxies, it has not been possible to detect

it. I will describe how, in the last year or so, the situation has changed,

with the detection of a cross-correlation between the thermal SZ effect and

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Mardi mar 03, 2015
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The cosmic microwave background contains a wealth of

information about cosmology as well as high energy physics. It tells

us about the composition and geometry of the universe, the properties

of neutrinos, dark matter, and even about the conditions in our

universe long before the cosmic microwave background was emitted.

After a brief review of what we may hope to learn from studies of the

cosmic microwave background about the early universe, I will review

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Mardi fév 24, 2015
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An exciting and largely unexplored frontier in observational and theoretical cosmology is to understand the properties of the universe between 400,000 years and one billion years after the big bang. Notably, the first galaxies formed in this time period, perhaps a few hundred million years after the big bang. These galaxies strongly influenced the gas in their surroundings as well as the formation of subsequent generations of galaxies. The early galaxies emitted ultraviolet light and ionized "bubbles" of hydrogen gas around them.

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Mardi fév 17, 2015
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It is well known that S-matrix Analyticity, Lorentz invariance and Unitarity place strong constraints on whether Effective Field Theories can be UV completed. A large class of gravitational field theories such as Massive Gravity and DGP inspired braneworld models contain as limits Galileon theories which in the past have been argued to violate the conditions necessary for a UV completion.

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Mardi fév 10, 2015
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The last years have seen a renewed interest in theories of massive gravity. They represent an infra-red modification of gravity where the gravitational force weakens at very large scales. Heuristically, they provide the playground to understand a possible modification of GR which could potentially provide a dynamical solution to the cosmological constant problem. In this talk I will discuss a number of theoretical aspects of massive gravity theories, focusing on the relevance of the so-called Vainstein mechanism, both at the classical and the quantum level.

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Mardi jan 27, 2015
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This talk will cover a number of fun topics related to studying and understanding the Cosmic Microwave Background, including where it came from, how it is like an inside-out star, CMB numerology, how much information it contains and how it is evolving in time.

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Mardi jan 20, 2015
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Models such as Natural Inflation that use Pseudo-Nambu-Goldstone bosons (PNGB's) as the inflaton are attractive for many reasons. However, they typically require trans-Planckian field excursions $\Delta \Phi>M_{\rm Pl}$, due to the need for an axion decay constant $f>M_{\rm Pl}$ to have both a sufficient number of e-folds {\em and} values of $n_s,\ r$ consistent with data.

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Mardi jan 13, 2015
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We explore the brightness frontier in time domain radio astronomy and its possible usefulness for cosmology. It is argued that the brightest known source of emission, Crab nanoshots, are caused by Schwinger pair production. The same mechanism may be the source of Fast Radio Bursts (FRBs) if this emission is form coalescing neutron stars. It is then shown how using FRBs as triggers can extend the reach of gravitational radiation and neutrino telescopes.

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Mardi déc 16, 2014

In this talk, I will review the main ideas underlying stochastic inflation, by introducing the formalism in two independent ways. First I will start from the intuitive picture stemming from the equations of motion of the system. I will then introduce a more rigorous approach based on the in-in formalism, and show how the usual set of Langevin equations can emerge from a path integral formulation. With this understanding, I will then formulate a new, recursive method which allows to solve consistently both in slow-roll parameters and in quantum corrections.

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Mardi déc 09, 2014
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We propose a new way to search for (hidden) cool molecular hydrogen H2 in the Galaxy through diffractive and refractive effects: Stars twinkle because their light crosses the atmosphere. The same phenomenon is expected on a longer time scale when the light of a remote star crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths.

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