Tracking Extended Quintessence

We study the cosmological role of a Tracking Field $\phi$ in Extended Quintessence scenarios (TEQ), where the dynamical vacuum energy driving the acceleration of the universe today is coupled with the Ricci scalar, $R$, with a term of the form $F(\phi)R/2$, where $F(\phi) = 1/8\pi G+\xi(\phi^{2}-\phi_{0}^{2})$. Tracker solutions for these NMC models, with inverse power-law potentials, possess an initial enhancement of the scalar field dynamics, named $R$-boost, caused by the Ricci scalar in the Klein-Gordon equation. During this phase the field performs a "gravitational" slow rolling which we model analytically, with energy density scaling as $(1+z)^{2}$. We evolve linear perturbations in TEQ models assuming Gaussian scale-invariant initial spectrum. We obtain significant changes in the Integrated Sachs Wolfe effect and in the acoustic peaks locations on the Cosmic Microwave Background, as well as in the turnover on the matter power spectrum. All these corrections may assume positive as well as negative values, depending on the sign of the NMC parameter $\xi$. We give analytical formulas describing all these effects. We show that they can be as large as $10 - 30$ with respect to equivalent cosmological constant and ordinary tracking Quintessence models, respecting all the existing experimental constraints on scalar-tensor theories of gravity. These results demonstrate that the next decade data will provide deep constraints on the nature of the dark energy in the Universe, as well as the structure of the theory of gravity.Comment: 24 pages including 8 figures, final version to be published in Phys.Rev.

Executive summary, overview, conclusions and recommendations

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An overview of the workshop on thermal remote sensing held at La Londe les Maures, France, September 20-24, 1993

This article reviews the major topics discussed at the Thermal Remote Sensing Workshop held at La Londe les Maures, France in 1993 and concludes with a list of new items and concepts suggested during the meeting. / Cet article résume les principaux thèmes abordés lors du séminaire sur la télédétection dans l'infrarouge thermique, organisé à la Londe Les Maures, France, en 1993, et conclut par des recommandations sur les concepts et les nouvelles approches proposées durant le séminaire