Modified gravity and cosmology
Antonio Padilla2012, Physics Reports
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Abstract
In this review we present a thoroughly comprehensive survey of recent work on modified theories of gravity and their cosmological consequences. Amongst other things, we cover General Relativity, Scalar-Tensor, Einstein-Aether, and Bimetric theories, as well as TeVeS, f (R), general higher-order theories, Hořava-Lifschitz gravity, Galileons, Ghost Condensates, and models of extra dimensions including Kaluza-Klein, Randall-Sundrum, DGP, and higher co-dimension braneworlds. We also review attempts to construct a Parameterised Post-Friedmannian formalism, that can be used to constrain deviations from General Relativity in cosmology, and that is suitable for comparison with data on the largest scales. These subjects have been intensively studied over the past decade, largely motivated by rapid progress in the field of observational cosmology that now allows, for the first time, precision tests of fundamental physics on the scale of the observable Universe. The purpose of this review is to provide a reference tool for researchers and students in cosmology and gravitational physics, as well as a self-contained, comprehensive and up-to-date introduction to the subject as a whole.
Key takeaways
- Theories that obey the EEP are often described as being 'metric' theories of gravity, as any theory of gravity based on a differentiable manifold and a metric tensor that couples to matter, as in Eq.
- In what follows we will consider gravitational experiments and observations that can potentially be used to distinguish between different metric theories of gravity.
- The three gravitational fields are the metric,g µν (with connection∇ a ), that we refer to as the Bekenstein metric, the Sanders vector field, A µ , and the scalar field, φ.
- As with many modifications to gravity, cosmological observables can be used to constrain f (R) theories of gravity.
- Unlike the case of f (R) theories of gravity, the theories described by the density given in Eq.
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