No abstract

The analysis of certain singularities in scalar-tensor gravity contained in a recent paper is completed, and situations are pointed out in which these singularities cannot occur.

Late time mild inflation (LTMI) proposes to solve the age of the universe problem and the discrepancy between locally and globally measured values of the Hubble parameter. However, the mechanism proposed to achieve LTMI is found to be physically pathological by applying the theory of tails for the solutions of wave equations in curved spaces. Alternative mechanisms for LTMI are discussed, and the relevance of scalar wave tails for cosmology is emphasized. * Also at Instituts Internationaux de Chimie et de Physique Solvay. 177 Int. J. Mod. Phys. D 1999.08:177-188. Downloaded from www.worldscientific.com by FLINDERS UNIVERSITY LIBRARY on 02/04/15. For personal use only. a Unfortunately, the terminology commonly used in the literature is misleading; it would be more appropriate to refer to the "Huygens' property" instead of the "Huygens' principle." Int. J. Mod. Phys. D 1999.08:177-188. Downloaded from www.worldscientific.com by FLINDERS UNIVERSITY LIBRARY on 02/04/15. For personal use only.

The interplay between cosmological expansion and local attraction in a gravitationally bound system is revisited in various regimes. First, weakly gravitating Newtonian systems are considered, followed by various exact solutions describing a relativistic central object embedded in a Friedmann universe. It is shown that the ``all or nothing'' behaviour recently discovered (i.e., weakly coupled systems are comoving while strongly coupled ones resist the cosmic expansion) is limited to the de Sitter background. New exact solutions are presented which describe black holes perfectly comoving with a generic Friedmann universe. The possibility of violating cosmic censorship for a black hole approaching the Big Rip is also discussed.Comment: 17 pages, LaTeX, to appear in Phys. Rev.

Hawking has proven that black holes which are stationary as the end point of gravitational collapse in Brans-Dicke theory (without a potential) are no different than in general relativity. We extend this proof to the much more general class of scalar-tensor and f(R) gravity theories, without assuming any symmetries apart from stationarity.