Research

I work on the intersection between cosmology, astrophysics and fundamental physics. I use gravitational waves, gravitational lensing, cosmic microwave background, large scale structure and other cosmological observations to test the laws of gravity and the nature of dark energy and dark matter. More recently, I am developing new methods to discover and characterize compact objects using gravitational waves and gravitational lensing.

For a full, updated account you can take a look at publication databases

or look at the brief descriptions of my work on gravitational lensing, dark matter & black holes, gravitational waves & tests of gravity, dark energy and cosmology, gravitatoinal theories and future gravitational-wave detectors.

Gravitational Lensing, Dark Matter and Black Holes

No LIGO MACHO Gravitational lensing effects probe the Universe's darkest objects: black holes and dark matter halos. The lack of gravitationally magnified type Ia supernovae sets bounds on the abundance of compact objects, ruling out LIGO-Virgo black holes as the dominant dark matter component. Supermassive black hole binaries can produce extreme magnifications of background stars: this will allow us to discover these systems and characterize their dynamics, including the emission of gravitational waves (GWs). The propagation of GWs provides valuable opportunties to illuminate dark objects: Lensing of GWs allows us to characterize gravitational lenses thanks to wave diffraction and interference, providing stringent limits on dark-matter objects and their morphology. My group has developed the GLoW code to investigate wave-optics lensing phenomena.

Selected publications:

Selected Talks:

↦ Lensing of GWs: New Opportunities for Fundamental Physicsr at Cosmo from Home (2024).

↦ GW lensing as a probe of cosmic structures and dark matter at LISA Symposium (2022).

↦ Talk and discussion on PBH constraints with lensing of SNe at CERN workshop (2018).

Gravitational Waves, Dark Energy and Tests of Gravity

Tests of lens-induced birefringence with GWTC-3 The discovery of gravitational waves (GW) offers new opportunities for the study of gravity and cosmology. My work contributed to understand GW propagation in theories beyond Einstein Gravity and anticipate the GW speed as the most powerful tool to confirm or discard a large classes of theories. The detection of GW170817, the first neutron-star merger, allowed a very precise measurement of the GW speed that spectacularly ruled out entire classes of gravity theories and dark energy models. GW lensing beyond Einstein's GR provides further opportunities: deviations from inhomogeneity mix the two GW polarizations, leading to birefringence and dispersion effects that can be tested with black hole mergers. We recently performed a search for birefringence on 43 GW events, setting stringent bounds on deviations from GR. The spin-orbit coupling between a GW and the background curvature can be observed for GWs emitted in the vicinity of a massive black hole.

Selected publications:

Review:

Selected Talks:

↦ Talks on GW lensing beyond GR at LISA Symposium 2020 (short) and SISSA Gravity webinars (long) .

↦ Talk on GWs and Dark Energy at DARKMOD conference, IPhT Saclay (2017).

Dark Energy and Cosmology

Galileon_H0_solutions Understanding dark energy, the mysterious source of the Universe's acceleration, is a major goal of observational and theoretical cosmology. My work has focused on ways to test different dark energy physics using cosmological and other data. I develop the hi_class code, an accurate, fast and flexible code to obtain cosmological predictions in general dark energy models. I have applied hi_class (and similar codes) to test gravity and scenarios for cosmic acceleration. Some of these models have interesting features: for instance, the covariant Galileon is able to reconcile the CMB and distance-ladder measurement of H0. We recently re-examined DESI's evidence for dynamical dark energy by performing a model independent reconstruction. Research in non-standard cosmologies is also useful to revise model-dependent assumption in data analysis techniques.

Selected publications:

Selected Talks:

↦ Review talk on Dark Energy at the EuCAPT Annual Symposium (2022).

↦ Talk on solutions to the H0 problem beyond GR at the Cosmology from Home Conference (2020).

↦ Lecture on alternative theories of gravity at the Cosmology School in the Canary Islands (2017).

Theories of Gravity

Islands of stability Beyond Horndeski Important insights into dark energy are often gained from theoretical considerations, which may reveal new possibilities or obstructions in known models. Redefinitions of the fundamental fields are a useful tools to examine extended theories of gravity. By using generalized field redefinitions, I presented the first examples of viable theories beyond Horndeski, previously thought to be the most general ghost-free theory of its class. Earlier I had used a more restricted field redefinition to show the equivalence between disformally coupled theories and DBI Galileons, generalizing the notion of the Einstein and Jordan frames.

Selected publications:

Selected Talk:

↦ Talk on beyond Horndeski theories at Extended Theories of Gravity in NORDITA (2015).

Future GW detectors

The LIGO-Virgo-Kagra network is just the beginning of GW astronomy: future detectors on the ground and in space will enable exquisite GW measurements, probing the furtherst depths of the universe and exploring new frequencie bands. I an contributing to develop the science case for these facilities.

Selected publications: