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 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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Tuesday Dec 02, 2008

I will review recent progress in testing with cosmological data the inflationary hypothesis for describing the very early universe. I will present snapshots of different aspects of confronting the theory with data, including a \'bottom-up\' approach: the latest results from a systematic reconstruction of the inflationary dynamics; and a \'top- down\' approach: testing specific string theoretic constructions that attempt to implement inflation, while predicting distinctive observables not found in simple field-theory models.

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Friday Nov 28, 2008

It has long been thought that theories based on equations of motion possessing derivatives of order higher than second are not unitary. Specifically, they are thought to possess unphysical ghost states with negative norm. However, it turns out that the appropriate Hilbert space for such theories had not been correctly constructed, and when the theory is formulated properly [Bender and Mannheim, PRL 100, 110402 (2008). (arXiv:0706.0207 [hep-th]] there are no ghost states at all and time evolution is fully unitary.

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Friday Nov 21, 2008
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Gravitomagnetism is a subtle concept. Adding Lorentz invariance to Newtonian gravity leads to magnetism, but Einsteinian gravitomagnetism differs from Maxwell\'s electromagnetism. The differences lead to confusion when Lense-Thirring precession is wrongly ascribed to gyroscopes, and when authors disagree about whether lunar laser ranging has measured gravitomagnetism. To clarify these issues, we analyze electric and magnetic effects in local Lorentz frames using the tetrad formalism.

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