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 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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Tuesday Feb 26, 2013

Newton’s inferences from phenomena realize an ideal of
empirical success that’s richer than prediction. To realize Newton’s richer
conception of empirical success a theory needs to do more than to accurately
predict the phenomena it purports to explain: in addition it needs to have the
phenomena accurately measure parameters of the theory. Newton’s method aims to
turn theoretical questions into ones which can be empirically answered by
measurements from phenomena.

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Tuesday Feb 05, 2013

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

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

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Tuesday Jan 22, 2013

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

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

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

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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