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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.

## Probing cosmic inflation: WMAP and beyond

Mardi fév 13, 2007
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Current measurements from WMAP and other cosmological probes are consistent with a simple inflationary model. Such models predict a background of gravitational waves which may soon be observable in the polarized component of the Cosmic Microwave Background.
However, WMAP has observed significant levels of polarized radiation from our galaxy, due to both synchrotron radiation and thermal dust emission.
A better understanding of this radiation will be vital if we are to correctly remove it and confidently detect an inflationary signal.

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## New cosmic maps & measurements

Jeudi fév 01, 2007
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I first summarize how the recent avalanche of precision measurements involving the cosmic microwave background, galaxy clustering, the Lyman alpha forest, gravitational lensing, supernovae Ia and other tools probes has transformed our understanding of our universe. I then discuss key open problems such as the nature of dark matter, dark energy and the early universe.

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## Quantum cosmology and the conditions at the birth of the universe

Mardi jan 30, 2007
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Cosmology ultimately aims to explain the initial conditions at the beginning of time and the entire subsequent evolution of the universe. The "beginning of time" can be understood in the Wheeler-DeWitt approach to quantum gravity, where homogeneous universes are described by a Schroedinger equation with a potential barrier. Quantum tunneling through the barrier is interpreted as a spontaneous creation of a small (Planck-size) closed universe, which then enters the regime of cosmological inflation and reaches an extremely large size.

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## Domain Lines as Fractional Strings

Mardi jan 23, 2007
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We consider N=2 supersymmetric quantum electrodynamics (SQED) with 2 flavors, the Fayet--Iliopoulos parameter, and a mass term $beta$ which breaks the extended supersymmetry down to N=1. The bulk theory has two vacua; at $beta=0$ the BPS-saturated domain wall interpolating between
them has a moduli space parameterized by a U(1) phase $sigma$ which can
be promoted to a scalar field in the effective low-energy theory on the
wall world-volume. At small nonvanishing $beta$ this field gets a
sine-Gordon potential. As a result, only two discrete degenerate BPS

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## Landau-Ginzburg perspective on Gregory-Laflamme instability

Mardi jan 16, 2007

I begin with a brief description of the black strings in backgrounds with compact circle, the Gregory-Laflamme instability and the resulting phase transition, and the critical dimensions.Then I describe a Landau-Ginzburg thermodynamic perspective on the instability and on the order of the phase transition. Next, the approach is generalized from a circle compactification to an arbitrary torus compactification. It is shown that the transition order depends only on the number of extended dimensions.

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## The strength of crystalline color superconductors

Mardi jan 09, 2007
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We discuss the properties of matter in the low temperature regime at density that may exist in the core of compact stars.
Assuming that in these conditions quarks are deconfined the attractive
color interaction determines the formation of Cooper pairs of quarks
and the resulting quark matter has properties analogous to standard
superconductors.
We show that under reasonable conditions a state were Cooper pairs
have non-zero total momentum is energetically favored and the
resulting non-homogeneous condensate is characterized by a crystal

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## Non-Gaussianity in multi-field inflation

Mardi déc 12, 2006

During multi-field Inflation, the curvature perturbation can evovlve on superhorizon scales and will develop non-gaussianity due to non-linear interactions. In this talk I will discuss the calculation of this effect for models of inflation with two scalar fields.

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## Folded Supersymmetry

Mardi déc 12, 2006
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## Generalized Modified Gravity Models: ghosts and dynamical bounds

Mardi nov 28, 2006
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Modified gravity models seem to have classical instabilities, ghosts degrees of freedom and superluminal modes. Besides these constraints new dynamical bounds have found to be typical of these models. The cosmological nature of all these constraints is discussed.

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## The nu physics in the dark sector

Mardi nov 28, 2006
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Existence of dark energy and nonzero nu mass are two most exciting discoveries of recent years. More excitingly, the similarity between the energy scales of these two raise the question: "Are they related?" I will explore how such connection could be there in nature and its cosmological consequences mainly in structure formation.

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