MG13 - Talk detail

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 Participant

Institution

Session

Accepted

Yes

Order

Time

Talk

Title

Abstract

A two-parameter family of spherically symmetric and time-dependent solutions of Brans-Dicke gravity, introduced to model space- and time-varying gravitational couplings, is analyzed. These solutions are supposed to represent central objects embedded in a spatially flat universe. The structure of these spacetimes is analyzed, focussing mostly on the presence and evolution of apparent horizons. We find that the solutions posses multiple evolving apparent horizons, both black hole horizons covering the central singularity and cosmological ones. It is not uncommon for two of these horizons to merge, leaving behind a naked singularity covered only by a cosmological horizon. The physical relevance of this family of solutions is discussed.

Session

Accepted

Yes

Order

Time

Talk

Title

Abstract

We perform a cosmographic analysis using several cosmological observables such as the luminosity distance moduli, the volume distance, the angular diameter distance and the Hubble parameter. We also present forecasts for the coefficients of the kinematic expansion using future but realistic data sets: constraints on these coefficients are likely to improve by a factor ten with the upcoming large scale structure probes. Finally, we derive the set of the cosmographic parameters for several cosmological models and compare them with our best fit set. We show that the inclusion of the Hubble data set leads to strong constraints on the lowest order coefficients and in particular it is incompatible with $\Lambda$CDM at 3-$\sigma$ confidence level. We discuss the reliability of this determination and suggest further observations.

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