SÉMINAIRE DU GRECO
"Some features of Scalar-Tensor Cosmologies" |
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Riccardo Catena |
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Scalar-Tensor theories of gravity provide a consistent framework to accomodate an ultra-light quintessence scalar field explaing the actual cosmic acceleration. In this class of cosmological models we focus on two quantities: the CDM relic abundance and the dark matter to baryon ration. Because of the modification in the expansion rate due to the scalar field added in the gravitational sector, we find an earlier decoupling for the CDM particles giving rise to a potentially very important enhancement of the CDM relic abundance. Moreover, this kind of models open the possibility to explain why the ratio between dark matter energy density and baryon energy density is roughly of order one today. This issue can not be explained in the LamdaCDM where such a ratio is a constant quantity, fixed by the two uncorrelated physical processes dark matter freeze out and baryogenesis. Admitting that baryons and dark matter couple differently to the same scalar field, the ratio between their energy densities becomes a field dependent quantity. We find an attractor mechanism that makes such a ratio dynamically relax to a ratio of coupling constants and so that its actual value becomes naturally of order one. We propose concrete realizations of the above discussed scenarios satisfying all the bounds coming from BBN, CMB, Supernovae and General Ralativity tests. |
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jeudi 27 janvier 2005 - 11:00 Salle des séminaires Évry Schatzman, Institut d'Astrophysique de Paris |
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