# Cosmology & Gravitation

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

## Seminar Series Events/Videos

Mar 3 2015 - 11:00am
Room #: 400
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Apr 7 2015 - 11:00am
Room #: 400
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Apr 13 2015 - 11:00am
Room #: 400
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Apr 14 2015 - 11:00am
Room #: 400
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Apr 21 2015 - 11:00am
Room #: 400
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Apr 28 2015 - 11:00am
Room #: 400
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## The Epoch of Reionization and the Lyman-alpha Forest

Tuesday Feb 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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## UV Properties of Galileons

Tuesday Feb 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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## Cosmology in Massive GravityLand

Tuesday Feb 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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## Some things you might not now about the CMB

Tuesday 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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## Spinodal Instabilities and Super-Planckian Excursions in Natural Inflation

Tuesday 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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## Crab Nanoshots, Fast Radio Bursts and Cosmology

Tuesday 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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## Stochastic Inflation Revisited: A Self-Consistent Recursive Approach and Applications

Tuesday Dec 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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## Search for hidden turbulent gas through interstellar scintillation

Tuesday Dec 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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## Measuring ultra-large scales with the Square Kilometre Array

Tuesday Dec 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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## Consistency relations from inflation to the Large Scale Structure

Thursday 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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## RECENT PUBLIC LECTURE

### Kendrick Smith, Perimeter Institute

Speaker: Kendrick Smith