This article is intended to review the recent developments in the Horndeski theory and its
generalization, which provide us with a systematic understanding of scalar–tensor theories …

This paper reviews scalar–tensor theories characterized by a Lagrangian that, despite the
presence of second-order derivatives, contains a single scalar degree of freedom. These …

A bstract We present all scalar-tensor Lagrangians that are cubic in second derivatives of a
scalar field, and that are degenerate, hence avoiding Ostrogradsky instabilities. Thanks to …

Gravitational waves (GWs) provide a new tool to probe the nature of dark energy (DE) and
the fundamental properties of gravity. We review the different ways in which GWs can be …

Mimetic gravity is a Weyl‐symmetric extension of General Relativity, related to the latter by a
singular disformal transformation, wherein the appearance of a dust‐like perfect fluid can …

We perform a Hamiltonian analysis of a large class of scalar-tensor Lagrangians which
depend quadratically on the second derivatives of a scalar field. By resorting to a convenient …

Most existing theories of dark energy and/or modified gravity, involving a scalar degree of
freedom, can be conveniently described within the framework of the Effective Theory of Dark …

f (Q) gravity is an extension of the symmetric teleparallel equivalent to general relativity
(STEGR). This work shows that based on the scalar-nonmetricity formulation, a scalar mode …

Invertible disformal transformations serve as a useful tool to explore ghost-free scalar-tensor
theories. In this paper, we construct a generalization of invertible disformal transformations …

The almost simultaneous detection of gravitational waves and a short gamma-ray burst from
a neutron star merger has put a tight constraint on the difference between the speed of …