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 Feb 19, 2009
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An astrophysical black hole is completely described with just two parameters: its mass and its dimensionless spin. A few dozen black holes have mass estimates, but until recently none had a reliable spin estimate. The first spins have now been measured for black holes in X-ray binaries.

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Tuesday Feb 17, 2009
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I will discuss the possibility that a 'Wilson line' degree of freedom can play the role of an inflaton in a warped flux compactification, in the context of the DBI inflationary scenario. I will show how warped DBI Wilson line inflation offers an attractive alternative to ordinary (position field) DBI inflation, inasmuch as observational and theoretical constraints get considerably relaxed. Thus, besides the large non-Gaussianities produced in DBI scenarios, Wilson lines allow for an observable amount of gravitational waves, within consistent approximations.

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Wednesday Feb 11, 2009
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We have only scratched the surface of the potential for using large-scale structure (LSS) as a probe of fundamental physics/cosmology, i.e., quantitatively, we have only measured a small fraction of a percent of the accessible LSS information. Future measurements will probe dark energy, inflation, dark matter properties, neutrino masses, modifications of gravity, etc. with unprecedented precision.

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Tuesday Feb 10, 2009
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Braneworlds are a fascinating way of hiding extra dimensions by confining ourselves to live on a brane. One particular model (Randall-Sundrum) has a link to string theory via living in anti de Sitter space. I'll describe how the ads/cft correspondence has been used to claim that a braneworld black hole would tell us how Hawking radiation back reacts on spacetime, thus solving one of the outstanding problems of quantum gravity - the ultimate fate of an evaporating black hole. I'll review evidence for this conjecture, ending with some recent work that shows it may be problematic.

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Tuesday Feb 03, 2009
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We examine the embedding of dark energy energy models based upon supergravity. We analyse the structure of the soft supersymmetry breaking terms in presence of dark energy. We pay attention to their dependence on the quintessence field and to the electroweak symmetry breaking, ie the pattern of fermions masses at low energy within the MSSM coupled to quintessence. In particular, we compute explicitly how the fermion masses generated through the Higgs mechanism depend on the quintessence field for a general model of quintessence.

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Tuesday Jan 20, 2009
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Inflationary scenarios with detectable primordial tensor perturbations typically require symmetries that can protect the potential over a super-Planckian field excursion. An old and natural idea is for the inflaton to be an axion protected by a shift symmetry. However, this has appeared difficult to realize in string theory because axion periodicities are sub-Planckian in known examples. I will explain how in compactifications containing wrapped fivebranes, the effective axion range is increased by monodromy: a single axion period can be traversed many times.

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Tuesday Jan 13, 2009

The growth of matter perturbations in the presence of dark energy with small fluctuations depends on the speed of sound of these fluctuations and the comoving scale. The growth index can differ from the value that it takes in the limit of no dark energy perturbations by an amount comparable to the accuracy of future observations. This may contribute to a better characterization of the dark energy properties.

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Tuesday Jan 06, 2009
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If primordial black holes are produced at the end of inflation, they should quickly decay via Hawking radiation. For the most part the radiation signature of these black holes will be wiped out, as the universe is still radiation dominated when they disappear. The exception to this would be a stochastic background of gravity waves. I present an algorithm by which the spectrum of radiation can be calculated, and discuss the dependence on the initial energy density and the number of relativistic species.

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Friday Dec 05, 2008
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I will show the calculation of the probability distribution for the volume of the Universe after slow-roll inflation both in the eternal and the non-eternal regime. Far from the eternal regime the probability distribution for the number of e-foldings, defined as one third of the logarithm of the volume, is sharply peaked around the number of e-foldings of the classical inflaton trajectory. At the transition to the eternal regime this probability is still peaked (with the width of order one e-foldings) around the average, which however gets twice larger at the transition point.

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