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Weekly Seminars for March 2008 Print E-mail

Tuesday 4th March 2008

ICRANet Pescara, Seminars Room

Speaker: Prof. G. Chardin and Dr. A. Benoit Lévy CNRS - Université d'Orsay 

Title: A symmetric matter-antimatter Milner Universe

Abstract: The standard model of cosmology predicts a surprising composition of the Universe, in which ordinary matter accounts for just 5 % of the Universe density, while the remaining 95% are supposedly composed of Dark Energy and Dark Matter, both unobserved. We propose here to study the unconventional cosmology of a symmetric Milne Universe, composed of matter and antimatter in equal quantities, and where antimatter has negative mass. In this Milne (coasting) cosmology, the expansion factor evolves linearly with time. After summarizing the motivations for such a surprising proposal, we show that this Milne cosmology meets rather remarkably the four classical cosmological tests of age, primordial nucleosynthesis, CMB and Type Ia supernovae. We discuss critically the open questions raised by this model.

Presentation: PDF

Wednesday 5st March 2008

ICRANet Pescara, Seminars Room 

Speaker: Dr. A. Benoit Lévy from CNRS/CSNS - Université Paris Sud ORSAY 

Title: Observational constraints of a Matter-Antimatter Symmetric Milne Universe

Abstract: The standard model of cosmology states a surprising composition of the Universe, in which ordinary matter accounts for just 5 %. The remaining 95% are composed of 70% Dark Energy and 25 % Dark Matter. However, those two components have never been identified and remain a challenging problem to modern cosmology. One alternative to the concordance model could be the symmetric Milne Universe, composed of matter and antimatter (supposed to have negative mass) in equal quantities. One important consequence is that the expansion factor evolves linearly with time throughout the whole story of the Universe. I will show what are the effects of such hypothesis to classical cosmological test such as primordial nucleosynthesis, CMB, or Type Ia supernovae.

 Presentation: PDF

Wednesday 12th March 2008

Università "La Sapienza" Roma - Aula 6 (Dip. Fisica Ed. "Fermi")

Speaker: Dr. Gregory V. Vereshchagin from ICRANet

Title: Thermalization of pair plasma with baryonic loading

Abstract: In the recent publications we considered the approach of nonequilibrium pair plasma towards thermal equilibrium state adopting kinetic treatment. We have shown that it is crucial to account for not only binary but also triple direct and inverse interactions between electrons, positrons and photons. In the present talk we present details of the computational scheme, as well as generalize out treatment, considering baryonic loading of the pair plasma. Special attention is given to the application of our results to cosmic gamma-ray bursts sources. Our conclusion remains the same: the plasma even with baryonic admixture reaches thermal equilibrium configuration on a timescale 10^{-12} sec, prior to expansion and thus hydrodynamic treatment adopted in the literature to model expansion of gamma-ray bursts sources can be applied.

 Presentation: PDF

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