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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 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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Mardi déc 02, 2014
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Forthcoming 21cm intensity mapping surveys on the Square Kilometre Array (SKA) will be capable of probing unprecedentedly large volumes of the Universe. This will make it possible to detect effects beyond the matter-radiation equality peak in the power spectrum, including primordial non-Gaussianity, GR corrections, and possible signatures of modified gravity. I give an overview of the proposed SKA intensity mapping surveys, the science that they will be able to do, and some of the challenges that they face.

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Jeudi nov 27, 2014
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According to the Newtonian intuition, a constant gravitational field has no physical effect on a system since it can always be redefined, and a homogeneous gradient of the gravitational field (i.e. a homogeneous gravitational force) is equivalent to an accelerated reference frame. I will show how to extend this intuition to cosmological scales; in the presence of a single clock a constant curvature perturbation and its gradient can be set to zero through a coordinate transformation.

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Mardi nov 25, 2014
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Velocity fields are a powerful probe of structure formation and the energy content of our Universe. Additionally, the motion of ionized gas on intermediate scales can be used to measure the clustering of baryons and shed light on galaxy formation and feedback mechanisms. I will discuss techniques that can be used to both constrain cosmology and measure baryon properties. I will also present some preliminary results.

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Jeudi nov 20, 2014
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A modified gravity (MOG) theory is explored that can explain current observational data in the present universe without detectable dark matter. This data includes galaxy rotation curves, cluster dynamics, gravitational lensing, globular clusters, the Bullet Cluster and solar system experiments. A vector field in the MOG action is a hidden, dark and massive photon that acts as a collisionless particle in the early universe and explains structure growth.

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Jeudi nov 13, 2014
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We are investigating modifications of general relativity that are operative at the largest observable scales. In this context, we are investigating the model of brane induced gravity in 6D, a higher dimensional generalization of the DGP model. As opposed to different claims in the literature, we have proven the quantum stability of the theory in a weakly coupling regime on a Minkowski background. In particular, we have shown that the Hamiltonian of the linear theory is bounded from below. This result opened a new window of opportunity for consistent modified Friedmann cosmologies.

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