Valerio Faraoni, Vincenzo Vitagliano, Thomas P. Sotiriou, Stefano Liberati
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. Two characteristic limits are also explicitly worked out: the limit where the theory reduces to general relativity and the limit where the solutions become static. The physical relevance of this family of solutions is discussed.
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http://arxiv.org/abs/1205.3945
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