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 …

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 …

The dawn of the twenty-first century came with very positive prospects for gravity, cosmology,
and astrophysics. Technological progress made it possible for cosmology to enter to its …

The discovery of cosmic acceleration has triggered a consistent body of theoretical work
aimed at modeling its phenomenology and understanding its fundamental physical nature …

Positivity bounds—constraints on any low-energy effective field theory imposed by the
fundamental axioms of unitarity, causality and locality in the UV—have recently been used to …

The first multi-messenger gravitational wave event has had a transformative effect on the
space of modified gravity models. In this paper we study the enhanced tests of gravity that …

We present the data-driven late-time reconstruction of gravitational theories and dark energy
models on cosmological scales. We showcase the power of present cosmological probes at …

We present new cosmological parameter constraints for general Horndeski scalar-tensor
theories, using CMB, redshift space distortion, matter power spectrum and BAO …

Positivity bounds—the consequences of requiring a unitary, causal, local UV completion—
place strong restrictions on theories of dark energy and/or modified gravity. We derive and …

Attempts at constraining theories of late time accelerated expansion often assume broad
priors for the parameters in their phenomenological description. Focusing on shift-symmetric …