Research

Full list of pubblications on ADS, Inspire, Google Scholar, or my CV.

Gravitational Waves

Astrophysical environmental effects

Brand new opportunities for fundamental physics and astrophysics are awaiting us in the next decade, thanks to gravitational wave astronomy.

For instance, we found that the LISA observatory will be able to detect astrophysical phenomena such as mass accretion directly from the gravitational emission of black hole binaries. Black hole binaries in gas-rich environments (like active galactic nuclei) could be affected by a number of other effects as well, which we investigated here.

Another source which could probe its environment are compact objects spiralling into accreting massive black holes (known as an extreme-mass-ratio inspirals, or EMRIs). We demonstrated that this was the case here. Recently, I have been thinking about modelling the interaction between the EMRI and the disk relativistically, in this paper.

Black hole ringdown and other black hole modes

Gravity is a complicated, non linear theory, but some of the gravitational signals we see are surprisingly simple. In recent work led by Marina de Amicis, we showed for the first time how the characteristic modes of a black hole, its quasinormal modes, turn on over time during the ringdown sourced by a second black hole.

I have also worked on the mathematical structure of black hole modes, such as their orthogonality. My collaborators and I constructed a product under which modes of Kerr black holes are orthogonal, here. The product can be used in perturbative calculations, as shown here in the context of superradiant clouds.

A few years ago, in this paper, my collaborators and I identified a new nonlinear effect in the very last stage of black hole mergers, the ringdown. We called this effect AIME, as in absorption-induced mode excitation, or love in French.

The evolution of massive black holes

There are many puzzles surrounding the formation and evolution of massive black holes. The future gravitational wave mission LISA will shed some light on the population of massive black hole binaries, but we need theoretical models to compare to current and future observations. I contributed to the development of a new model for the formation of massive black holes, which we called POMPOCO (like the studio Ghibli movie!). The model can be used to infer physical parameters from current observations (like the black hole luminosity function, including by JWST) and predict what LISA will see.

Galactic binaries

Mass accretion is also a common phenomenon in other LISA sources, such as black hole-white dwarf binaries. I found some interesting new relations in these systems with Alexandre Toubiana and Cole Miller.

Plasma-photon interactions around black holes

Electromagnetic waves can be confined around a black hole by the presence of plasma (courtesy of the interstellar medium, or an accretion disk). We have been exploring this phenomenon in a rigorous way in a series of papers: one and two. So far, we have sticked to linear theory. However, we know that nonlinearities can be very important in this system (potentially quenching instabilities), so tackling them will be our next step.

Dark Matter

Understanding the nature of dark matter is one of the most pressing problems in fundamental physics. Fortunately, astrophysical observations offer many opportunities to constrain dark matter interactions. My collaborators and I studied the propagation of light through a class of promising dark matter candidates, axion-like particles: more here and here.

Quantum Cosmology

Some physics questions, like the role of quantum field theory in determining the cosmological constant, or the very beginning of the Universe, can receive very little imput from observations. My colleagues and I are using semiclassical gravity to tackle these problems (here and here). In these calculations, we use real time (Lorentzian) gravitational path integrals, a rigorous tool to compute transitions in the geometry of the universe.

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