Abstract
Several different explicit reconstructions of gravity are obtained from the background Friedmann-Laîmatre-Robertson-Walker expansion history. It is shown that the only theory whose Lagrangian is a simple function of the Ricci scalar , that admits an exact expansion history, is standard general relativity with a positive cosmological constant and the only way to obtain this behavior of the scale factor for more general functions of is to add additional degrees of freedom to the matter sector.
- Received 12 May 2010
DOI:https://doi.org/10.1103/PhysRevD.82.023519
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