MG12 - Talk detail
 

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Abstract

Relativistic Accelerating Cosmology Driven by Cold Dark Matter

A new accelerating flat model with no dark energy that is fully dominated by cold dark matter (CDM) is proposed. The number of CDM particles is not conserved and the present accelerating stage is a consequence of the negative pressure describing the irreversible process of gravitational particle creation. In this model, the present Hubble parameter does not need to be small in order to solve the age problem and the transition happens even if the matter creation is negligible during the radiation and part of the matter-dominated phase. Therefore, instead of the vacuum dominance at redshifts of the order of a few, the present accelerating stage in this sort of Einstein–de Sitter CDM cosmology is a consequence of the gravitational particle creation process. As an extra bonus, in the present scenario the coincidence problem does not exist which plagues models with dominance of dark energy. The model is able to harmonize a CDM picture with the present age of the universe, the latest measurements of the Hubble parameter and the supernovae observations.

Acessing the Acceleration of the Universe with Sunyaev-Zeldovich and X-ray data from Galaxy Clusters

A kinematic method to access cosmic acceleration based exclusively on the Sunyaev-Zel'dovich effect (SZE) and X-ray surface brightness data from galaxy clusters is proposed. By using the SZE/X-ray data from 38 galaxy clusters [Bonamente et al. 2006] we find that the present Universe is accelerating and that the transition from an earlier decelerating to a late time accelerating regime occurred relatively recent. Such results are fully independent on the validity of any metric gravity theory, the possible matter-energy contents filling the Universe, as well as on the SNe Ia Hubble diagram from which the presenting accelerating stage was inferred. The ability of the ongoing Planck satellite mission to obtain tighter constraints on the expansion history through SZE/X-ray angular diameters is also discussed. It is argued that such a technique will be competitive with supernova data besides being complementary to it.

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