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 Feb 05, 2013
Speaker(s): 

The presence of additional light fields during inflation
can source isocurvature fluctuations, which can cause the curvature
perturbation $\zeta$, and its statistics to evolve on superhorizon scales. I
will demonstrate that if these fluctuations have not completely decayed before
the onset of perturbative reheating, then primordial observables such as the
level of non--Gaussianity can develop substantial reheating dependant
corrections. I will argue that for inflationary models where an adiabatic

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Tuesday Jan 29, 2013
Speaker(s): 

We apply CMB lensing techniques to large scale structure
and solve for the 3-D cosmic tidal field. We use small scale filamentary
structures to solve for the large scale tidal shear and gravitational
potential.

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Tuesday Jan 22, 2013
Speaker(s): 

In my talk I will discuss our recent paper
hep-th/1211.1322 where we construct a 3D conformal field theory dual to
asymptotically AdS cosmology in four dimensions. Due to the scale invariance
this dual theory allows an infinite family of instantons each of which breaks
the conformal group O(3,2) down to O(3,1). These instantons are dual to bulk
instantons responsible for nucleating an O(3,1) invariant cosmological
bubble.  Presumably they indicate an
infinite instability rate, however we are able to sum over all of them

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Tuesday Jan 15, 2013
Speaker(s): 

When recent observational evidence and the GR+FRW+CDM
model are combined we obtain the result that the Universe is accelerating,
where the acceleration is due to some not-yet-understood "dark
sector". There has been a considerable number of theoretical models
constructed in an attempt to provide an "understanding" of the dark

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Tuesday Jan 08, 2013
Speaker(s): 

Dark energy coupled to Standard Model fermions and gauge
bosons gives rise to fifth forces and new particles, which are readily
accessible to experiments from laboratory to cosmological scales.  I will discuss chameleon and symmetron
models, whose fifth forces are screened locally through large effective masses
and symmetry-restoring phase transitions, respectively.  Fifth force experiments such as the Eot-Wash
torsion balance will test chameleons with small quantum corrections and

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Tuesday Dec 11, 2012
Speaker(s): 

Fluctuations in the cosmic
microwave background (CMB) contain information which has been pivotal in
establishing the current cosmological model. These data can also be used to
test well-motivated additions to this model, such as
cosmic textures. Textures are a type of topological defect that
can be produced during a cosmological phase transition in the early universe,
and which leave characteristic hot and cold spots in the CMB. We apply Bayesian
methods to carry out an optimal test of the texture hypothesis, using

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Tuesday Dec 11, 2012
Speaker(s): 

We expound several principles in an attempt to clarify
the debate over infrared loop corrections to the primordial scalar and tensor
power spectra from inflation. Among other things we note that existing
proposals for nonlinear extensions of the scalar fluctuation field $\zeta$
introduce new ultraviolet divergences which no one understands how to
renormalize. Loop corrections and higher correlators of these putative
observables would also be enhanced by inverse powers of the slow roll parameter

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Thursday Dec 06, 2012
Speaker(s): 

Cosmological
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
Speaker(s): 

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

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Thursday Nov 22, 2012
Speaker(s): 

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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