The cosmic coincidence in Brans-Dicke cosmologies
Abstract
Among the suggested solutions to the cosmological constant problem, we find the idea of a dynamic vacuum, with an energy density decaying with the universe expansion. We investigate the possibility of a variation in the gravitational constant as well, induced, at the cosmological scale, by the vacuum decay. We consider an effective Brans-Dicke theory in the spatially flat FLRW spacetime, finding late time solutions characterized by a constant ratio between the matter and vacuum energy densities. By using the observed limits for the universe age, we fix the only free parameter of our solutions, obtaining a relative matter density in the range 0.25-0.4. In particular, for Ht = 1 we obtain a relative matter density equals to 1/3. This constitutes a possible explanation for another problem related to the cosmological term, the cosmic coincidence problem.
Cite
@article{arxiv.gr-qc/0505121,
title = {The cosmic coincidence in Brans-Dicke cosmologies},
author = {Saulo Carneiro},
journal= {arXiv preprint arXiv:gr-qc/0505121},
year = {2011}
}
Comments
This essay received an "honorable mention" in the 2005 Essay Competition of the Gravity Research Foundation