Abstract The Laser Interferometer Space Antenna (LISA) has two scientific objectives of
cosmological focus: to probe the expansion rate of the universe, and to understand …

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 …

The observation of GW170817 and its electromagnetic counterpart implies that gravitational
waves travel at the speed of light, with deviations smaller than a few× 10-15. We discuss the …

A bstract Positivity bounds are powerful tools to constrain effective field theories. Utilizing the
partial wave expansion in the dispersion relation and the full crossing symmetry of the …

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 …

A century ago, Einstein formulated his elegant and elaborate theory of General Relativity,
which has so far withstood a multitude of empirical tests with remarkable success …

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 …

Understanding the reason for the observed accelerated expansion of the Universe
represents one of the fundamental open questions in physics. In cosmology, a classification …

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 …

We review recent progress in the construction of modified gravity models as alternatives to
dark energy as well as the development of cosmological tests of gravity. Einstein's theory of …