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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.


Mardi sep 24, 2013

I'll discuss a
number of insights into the process of nonlinear structure formation which come
from the study of random walks crossing a suitably chosen barrier.  These
derive from a number of new results about walks with correlated steps, and
include a unified framework for the peaks and excursion set frameworks for
estimating halo abundances, evolution and clustering, as well as nonlinear,
nonlocal and stochastic halo bias, all of which matter for the next generation
of large scale structure datasets.

Scientific Areas: 


Mardi sep 17, 2013

ΛCDM has become the standard cosmological model because its
predictions agree so well with observations of the cosmic microwave background
and the large-scale structure of the universe. However ΛCDM has faced
challenges on smaller scales. Some of these challenges, including the “angular
momentum catastrophe" and the absence of density cusps in the centers of
small galaxies, may be overcome with improvements in simulation resolution and
feedback. Recent simulations appear to form realistic galaxies in agreement

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Mardi sep 03, 2013

I will review recent developments in our theoretical understanding of the abundance and clustering of dark matter haloes. In the first part of this talk, I will discuss a toy model based on the statistics of peaks  of Gaussian random field (Bardeen et al 1986) and show how the clustering properties of such a point set can be easily derived from a generalised local bias expansion. In the second part, I will explain how  this peak formalism relates to the excursion set approach and present parameter-free predictions for the  mass function and bias of dark matter halos.

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Mardi juil 30, 2013

employ the effective field theory approach for multi-field inflation which is a
generalization of Weinberg's work. In this method the first correction terms in
addition to standard terms in the Lagrangian have been considered. These terms
contain up to the fourth derivative of the fields including the scalar field
and the metric. The results show the possible shapes of the interaction terms
resulting eventually in non-Gaussianity in a general formalism. In addition
generally the speed of sound is different but almost unity. Since in this

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Mardi mai 14, 2013

Screened Scalar-Tensor gravity such as chameleon and symmetron theories allow order one deviations from General Relativity on large scales whilst satisfying all local solar-system constraints. A lot of recent work has therefore focused on searching for observational signatures of these

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Mardi mai 07, 2013
Ultra-light axions (m_a
I will also present preliminary results of constraints to this model using up-to-date cosmological observations, which verify the above picture. The parameter space is interesting to explore due to a strongly mass dependent covariance matrix, motivating comparisons between Metropolis-Hastings and nested sampling. Finally I discuss fine-tuning and naturalness in these models.
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Mardi avr 30, 2013

The non-Gaussian statistics of
the primordial density perturbation have become a key test of the inflationary
scenario of the very early universe. Currently many techniques are used to
calculate the non-Gaussian signatures of a given model of inflation. In
particular, simple super-horizon techniques such as the deltaN formalism are
often used for models with more than one field, while more technical field
theory techniques, referred to as the In-In formalism, are typically used for

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Mardi avr 23, 2013

I will present recent work,
done in collaboration with Daniel Roberts, on the global memory of initial
conditions that is sometimes, but not always, retained by fluctuating fields on
de Sitter space, Euclidean anti de Sitter space, and regular infinite trees. I
will discuss applications to the structure of configuration space in de Sitter
space and eternal inflation.

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Mardi avr 16, 2013

Cosmological results
from Planck, a third-generation satellite mission to measure the cosmic
microwave background, have just been announced.  These results improve
constraints on essentially all cosmological parameters, and have implications
for several preexisting sources of tension with the standard cosmological
model, while also raising new puzzles.  I will discuss these results and
their significance, as well as the next steps forward.

Scientific Areas: 


Jeudi avr 11, 2013

Already the last decade has
witnessed unprecedented progress in the collection of cosmological data.
Presently proposed and designed future cosmological probes and surveys permit
us to anticipate the upcoming avalanche of cosmological information during the
next decades.

The increase of valuable observations needs to be accompanied with the development
of efficient and accurate information processing technology in order to analyse
and interpret this data. In particular, cosmography projects, aiming at studying

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