# 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.

## Cosmology of Axions and Moduli

Thursday May 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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Tuesday May 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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## Cosmic Magnetic Fields

Monday Apr 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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## Density Perturbations from Curvatons Revisited

Tuesday Apr 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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## UV Sensitivity of Dark Matter

Tuesday Apr 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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## What Can Stellar Kinematics Tell Us About Dark Matter in Dwarf Galaxies?

Tuesday Apr 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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## Some new things to do with the CMB and galaxy surveys

Tuesday 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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## G-Bounce

Monday 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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## From Massive Gravity to Interacting Spin-2 Fields

Tuesday Mar 06, 2012
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Recent progress in massive gravity has made it possible to construct consistent theories of interacting spin-2 fields.  In this talk I'll describe these developments, focusing on the resolution of the Boulware-Deser ghost problem and the promotion of massive gravity to a bimetric theory of gravity with two dynamical, interacting spin-2 fields.  I'll then discuss the generalization of these bimetric theories to theories of multiple interacting spin-2 fields.

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## Dipoles in the Sky

Tuesday Feb 28, 2012
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The standard cosmological model posits that the universe is homogeneous and statistically isotropic on its largest scales. However, there is no fundamental reason why these properties have to hold, and in fact they can be broken due to interesting new physics. Moreover, there is some evidence from recent WMAP observations for 'anomalies' - including departures from statistical isotropy - on the largest observable scales.

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## LECTURES ON-DEMAND

### Roger Melko: Perimeter Institute and University of Waterloo

Speaker: Roger Melko