The Cosmic Microwave Background and Scalar-Tensor Theories of Gravity

Abstract

We show that if all observers see an isotropic cosmic microwave background in an expanding geodesic perfect fluid spacetime within a scalar-tensor theory of gravity, then that spacetime must be isotropic and spatially homogeneous. This result generalizes the Ehlers-Geren-Sachs Theorem of General Relativity, and serves to underpin the important result that any evolving cosmological model in a scalar-tensor theory that is compatible with observations must be almost Friedmann-Lemaitre-Robertson-Walker.

6 pages, REVTeX. To appear in Phys. Rev. D

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