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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.

 

Jeudi oct 25, 2012
Speaker(s): 

Chameleon gravity is
a scalar-tensor theory that mimics general relativity in the Solar System. The
scalar degree of freedom is hidden in high-density environments because the
effective mass of the chameleon scalar depends on the trace of the
stress-energy tensor.  In the early Universe, when the trace of the
stress-energy tensor is nearly zero, the chameleon is very light and Hubble
friction prevents it from reaching its potential minimum.  Whenever a
particle species becomes non-relativistic, however, the trace of the

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Mardi oct 16, 2012
Speaker(s): 

I review some recent developments in attempting to reconcile
the observed galaxy population with numerical models of structure formation in
the 'LCDM' concordance cosmology. Focussing on behaviour of dwarf galaxies, I
describe the infamous 'cusp-core' dichotomy -- a long-standing challenge to the
LCDM picture on small scales -- and use toy models to show how it is resolved
in recent numerical simulations (Pontzen & Governato 2012). I then discuss
the current observational status of this picture (Teyssier, Pontzen & Read

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Mardi oct 09, 2012
Speaker(s): 

Cosmic voids are potentially a rich source of information
for both astrophysics and cosmology. To enable such science, we produce the
most comprehensive void catalog to date using the Sloan Digital Sky Survey Data
Release 7 main sample out to redshift z = 0.2 and the Luminous Red Galaxy
sample out to z = 0.44. Using a modified version of the parameter-free void
finder ZOBOV, we fully take into account the presence of survey boundary and
masks. We discuss basic catalog statistics such as number counts and redshift

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Mardi oct 09, 2012
Speaker(s): 

There are many situations in cosmology that
motivate the study of scalar fields with higher-derivative actions. The best-known
such situations are probably k-inflation (with DBI-inflation being a special
case) and models based on galileon theories, but even eternal inflation and
cyclic universes provide good reasons to study such theories. After an extended
discussion of the motivations, I will show how scalar field theories with
higher derivatives can be constructed in (minimal, 4-dimensional) supergravity,

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Mardi oct 02, 2012
Speaker(s): 

The question of finite range gravity, or equivalently,
whether graviton can have a non-zero mass, has been one of the major challenges
in classical field theory for the last 70 years.

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Mardi sep 25, 2012
Speaker(s): 

We consider the stellar-dynamical processes which lead to
the capture or tidal disruption of stars by a supermassive black hole, review
the standard theory of two-body relaxation and loss-cone repopulation in
spherical galactic nuclei, and extend it to the axisymmetric and triaxial
nuclear star clusters.

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Mardi sep 18, 2012
Speaker(s): 

The idea that the graviton may be massive has seen a
resurgence of interest due to recent progress which has overcome its

traditional problems.  
I will review this recent progress, which has

led to a consistent ghost-free effective field theory of
a massive graviton, with a stable hierarchy between the graviton mass and the
cutoff, and how this theory has the potential to resolve the naturalness
problem of the cosmological constant.

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Mardi sep 11, 2012
Speaker(s): 

The spectrum of the cosmic microwave background (CMB) is known to be extremely close to a perfect blackbody. However, even within standard cosmology several processes occurring in the early Universe lead to distortions of the CMB at a level that might become observable in the future. This could open an exciting new window to early Universe physics.

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Mardi sep 04, 2012
Speaker(s): 

I will describe a new, generic mechanism for realizing a
period of slowly-rolling inflation through the use of an analog of 'magnetic
drift.' I will demonstrate how the mechanism works through two particular
worked examples: Chromo-Natural Inflation, which exists as a purely 4D
effective theory, and a version that can appear naturally in string theory.

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Mardi aoû 14, 2012
Speaker(s): 

I will introduce the theory and experimental technique of extra-solar planet observation by the gravitational microlensing and give a report on recent results. Then I will discuss the wave optics features in the gravitational microlensing, the analogy of this effect in the astronomical scales to the Young's double slit experiment. Finally I will discuss about the possibility of observation of diffraction patterns in the microlensing experiment.

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