Gravitational Waves
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. In another recent study, we also demonstrated that LISA could detect accretion disk effects when single compact objects spiral into the centre of the disk (known as an extreme-mass-ratio inspiral, or EMRI).
Black hole ringdown
Gravity is a complicated, non linear theory, but some of the gravitational signals we see are surprisingly simple. 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.
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.