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.


Tuesday Jul 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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Tuesday May 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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Tuesday May 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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Tuesday Apr 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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Tuesday Apr 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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Tuesday Apr 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.

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Thursday Apr 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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Tuesday Apr 09, 2013

The endgame of massive star evolution is the gravitational-induced collapse of the central inert iron core.  The collapse of the core continues until the matter reaches nuclear densities where the strong force between nucleons becomes dominant and provides sufficient pressure to stabilize the newly formed protoneutron star.  What ensues is a complex multi-physics problem involving strong gravity, multidimensional hydrodynamic instabilities, magnetic fields, multispecies neutrino radiation, and supranuclear density physics to name a few.

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Tuesday Mar 19, 2013

An analytical understanding of large-scale matter
inhomogeneities is an important cornerstone of our cosmological model and helps
us interpreting current and future data. The standard approach, namely Eulerian
perturbation theory, is unsatisfactory for at least three reasons: there is no
clear expansion parameter since the density contrast is not small everywhere;
it does not consistently account for deviations at large scales from a perfect
pressureless fluid induced by short-scale non-linearities; for generic initial

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Tuesday Mar 12, 2013

We apply the effective field theory approach to
quasi-single field inflation, which contains an additional scalar field with
Hubble scale mass other than inflaton. 
Based on the time-dependent spatial diffeomorphism, which is not broken
by the time-dependent background evolution, the most generic action of
quasi-single field inflation is constructed up to third order
fluctuations.  Using the obtained action,
the effects of the additional massive scalar field on the primordial curvature
perturbations are discussed.  In

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