A number of challenges to the standard Λ CDM model have been emerging during the past
few years as the accuracy of cosmological observations improves. In this review we discuss …

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 …

After a decade and a half of research motivated by the accelerating universe, theory and
experiment have reached a certain level of maturity. The development of theoretical models …

We construct four-dimensional covariant nonlinear theories of massive gravity which are
ghost-free in the decoupling limit to all orders. These theories resum explicitly all the …

We review recent progress in massive gravity. We start by showing how different theories of
massive gravity emerge from a higher-dimensional theory of general relativity, leading to the …

In the Dvali-Gabadadze-Porrati (DGP) model, the “self-accelerating” solution is plagued by a
ghost instability, which makes the solution untenable. This fact, as well as all interesting …

We determine the most general scalar field theories which have an action that depends on
derivatives of order two or less, and have equations of motion that stay second order and …

We consider the Lagrangian of gravity covariantly amended by the mass and polynomial
interaction terms with arbitrary coefficients and reinvestigate the consistency of such a theory …

Massive gravity has seen a resurgence of interest due to recent progress which has
overcome its traditional problems, yielding an avenue for addressing important open …

We review recent developments and results in testing general relativity (GR) at cosmological
scales. The subject has witnessed rapid growth during the last two decades with the aim of …