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 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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Tuesday Nov 18, 2008
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It is argued that space-time is discretized on the basis of the gravitational interactions among the degrees of freedom of quantum fields.Configurations of fields fall into 2 classes,propagating (cisplanckian in length scale) and those that are transplanckian, sequestered in the space-time that is localized in discrete elements.Only the former determine the hubble expansion parameter and are therefore used to construct the inflaton.The model used for discretization is Sorkin\'s causet construction.From this the covariant massy Klein Gordon equation can be rationalized.The mass is encoded a

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Friday Nov 14, 2008
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I will illustrate the case of interacting dark Energy, that is to say cosmologies in which the dark energy scalar field interacts with other things in the universe (gravity, cold dark matter or neutrinos).

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Tuesday Nov 11, 2008

The Lee-Wick model has recently been put forwards as an alternative to supersymmetry for solving the hierarchy problem of particle physics. I will show that, modulo important consistency questions, coupling the Lee-Wick model to cosmology leads to a bouncing universe cosmology with a scale-invariant spectrum of cosmological fluctuations emerging from quantum vacuum fluctuations in the contracting phase.

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Thursday Oct 30, 2008
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The Cosmic Microwave Background Radiation is our most important source of information about the early universe. Many of its features are in good agreement with the predictions of the so-called standard model of cosmology -- the Lambda Cold Dark Matter Inflationary Big Bang. However, the large-angle correlations in the microwave background exhibit several statistically significant anomalies compared to the predictions of the standard model. On the one hand, the lowest multipoles seem to be correlated not just with each other but with the geometry of the solar system.

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Tuesday Oct 28, 2008
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The Dark Energy might constitute an observable fraction of the total energy density of our Universe as far back as the time of matter radiation equality or even big bang nucleosynthesis. In this talk, I will review the cosmological implications of such an \'Early Dark Energy\' component, and discuss how it might - or might not - be detected by observations. In particular, I will show how assuming the early dark energy to be negligible will bias the interpretation of cosmological data.

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