# 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.

## Domain Lines as Fractional Strings

Tuesday 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

Tuesday 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

Tuesday 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

Tuesday Dec 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

Tuesday Dec 12, 2006
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## Generalized Modified Gravity Models: ghosts and dynamical bounds

Tuesday 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

Tuesday 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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## Is Brane Inflation Eternal?

Tuesday Nov 21, 2006
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It will be shown that eternal inflation of the random walk type is generically absent in the brane inflationary scenario. Eternal inflation will be analysed both in the context of KKLMMT and the DBI inflationary models. A Langevin analysis will be employed for a more careful treatment. The DBI action, and the relativistic nature of the brane motion in DBI inflationary model, leads to new subtleties in formulating a Langevin approach.

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## Leading Log Solution for Yukawa During Inflation

Tuesday Nov 14, 2006
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TBA

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## Dark matter: from the early Universe to the Milky Way

Tuesday Nov 07, 2006
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The initial conditions for structure formation, and hence the dark matter distribution on sub-galactic scales, depend on the microphysics of the dark matter in the early Universe. I will focus on WIMPs and explain how collisional damping and free-streaming erase perturbations on comoving scales k> ~1/pc. Consequently the first structures to form in the Universe are mini-halos with mass of order the Earth. I will then describe the status of calculations of the subsequent dynamical evolution of these mini-halos. Finally, if time permits, I'll briefly overview the microphysics of axions.

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