General Relativity has shown an outstanding observational success in the scales where it
has been directly tested. However, modifications have been intensively explored in the …

We derive the quadratic action for the physical degrees of freedom of massless spin-0, spin-
1, and spin-2 perturbations on a Schwarzschild-(A) dS background in arbitrary dimensions …

Ghost-free theories beyond the Horndeski class exhibit a partial breaking of the Vainshtein
mechanism inside nonrelativistic sources of finite extent. We exploit this breaking to identify …

Nonlinear, ghost-free massive gravity has two tensor fields; when both are dynamical, the
mass of the graviton can lead to cosmic acceleration that agrees with background data, even …

A new theory of gravity called Eddington-inspired Born–Infeld (EiBI) gravity was recently
proposed by Bañados and Ferreira. This theory leads to some exciting new features, such …

We present a comprehensive analysis of classical scalar, vector and tensor cosmological
perturbations in ghost-free massive bigravity. In particular, we find the full evolution …

Regardless of the long history of gauge theories, it is not well recognized under which
condition gauge fixing at the action level is legitimate. We address this issue from the …

Teleparallel gravity is a formulation of general relativity that is physically equivalent to metric
gravity if the gravitational action has the Einstein-Hilbert form and matter is minimally …

Bimetric gravity theories allow for many different types of cosmological solutions, but not all
of them are theoretically allowed. In this work we discuss the conditions to satisfy the Higuchi …

I discuss singular loci in the phase spaces of theories which lack globally well-defined
numbers of dynamical modes. This is a topic which appears quite often in the recent …