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.


Thursday Dec 06, 2012

birefringence is a postulated rotation of the linear polarization of photons
that arises due to a Chern-Simons coupling of a new scalar field to
electromagnetism. In particular, it appears as a generic feature of simple
quintessence models for Dark Energy, and therefore, should it be detected,
could provide insight into the microphysics of cosmic acceleration. Prior work
has sought this rotation, assuming the rotation angle to be uniform across the
sky, by looking for the parity-violating TB and EB correlations in the CMB

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Tuesday Nov 27, 2012

The stress-energy tensor in a conformal field theory has
zero trace.

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Thursday Nov 22, 2012

Holographic cosmology maps cosmological time evolution to
the inverse RG flow of a dual three-dimensional QFT. In cases where this RG flow
connects two closely separated fixed points, QFT correlators may be calculated
perturbatively in terms of the conformal field theory associated with one of the
fixed points, even when the dual QFT is at strong  coupling. 
Realising slow-roll inflation in these terms, we show how to derive
standard slow-roll inflationary power spectra and non-Gaussianities through

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Tuesday Nov 20, 2012

After a brief overview of electroweak baryogenesis,  I will show how to construct a solution of
the Dirac equation for a CP violating kink wall. This solution nicely reduces
to the known solution for a CP violating thin (step) wall.  The novel solution can be helpful for studies
of baryogenesis sources at strong first order phase transitions, which is
relevant for electroweak scale baryogenesis studies.

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Thursday Nov 15, 2012

In this talk I will
discuss a cosmological model where primordial inflation is driven by a `solid',
defined as a system of three derivatively coupled scalar fields obeying certain
symmetries and spontaneously breaking a certain subgroup of these. The symmetry
breaking pattern differs drastically from that of standard inflationary models:
time translations are unbroken. This prevents our model from fitting into the
standard effective field theory description of adiabatic perturbations. Consequently,

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Tuesday Nov 13, 2012

The de Sitter S-matrix provides a gauge-invariant and
field redefinition-invariant window into de Sitter QFTs and may provide a
crucial entry in any dS/CFT dictionary. In this talk I will summarize recent
progress on developing the S-matrix for theories with gauge fields and
perturbative gravity. Nonrenormalization theorems, hints of supersymmetry, and
perturbative stability will be discussed.

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Tuesday Nov 06, 2012

There are indications of a lower bound on magnetic fields
in the intergalactic media. Since magnetic fields on such large scales are
difficult to generate in the late universe, this might point to inflationary
magnetogenesis as the origin of intergalactic magnetic fields. If the magnetic
fields are generated during inflation, they are naturally correlated with the
inflaton perturbations in a general class of models. This leads to a
consistency relation between the power spectrum of primordial magnetic fields

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Thursday Oct 25, 2012

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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Tuesday Oct 16, 2012

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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Tuesday Oct 09, 2012

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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