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We analyse cosmological perturbations around a homogeneous and isotropic background for scalar-tensor, vector-tensor and bimetric theories of gravity. Building on previous results, we propose a unified view of the effective parameters of all these theories. Based on this structure, we explore the vi ...

The detection of an electromagnetic counterpart (GRB 170817A) to the gravitational-wave signal (GW170817) from the merger of two neutron stars opens a completely new arena for testing theories of gravity. We show that this measurement allows us to place stringent constraints on general scalar-tensor ...

Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, ▫$\lambda$▫CDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the part ...