MG12 - Talk detail
 

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 Participant 

Institution

Session

Talk

Abstract

Is f(R) gravity viable? The Cauchy problem for metric and Palatini f(R) theories

General criteria for the viability of metric and Palatini f(R) gravity will be reviewed. In particular, the Cauchy problem for these theories will be discussed. For metric f(R) gravity the latter is well-posed in vacuo and well-formulated in the presence of ``reasonable'' forms of matter. For Palatini f(R) gravity the initial value problem is well-posed in vacuo and in the presence of matter with constant trace of the energy-momentum tensor (including conformal matter), and most likely ill-formulated otherwise.

Cosmological expansion and local dynamics

Assuming that the Friedmann metric is valid down to small scales, do local objects expand with the universe or resist the expansion? This long-standing issue will be revisited with the help of new exact solutions describing black holes embedded in cosmological backgrounds. Unless the background is de Sitter (for which Price finds an ``all-or-nothing behaviour''), even the most strongly bound object, the black hole, participates in the expansion of the cosmic substratum. Issues of interpretation and genericity of the new exact solutions will be discussed.

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