In this page I give a basic overview of the general topics and motivations of my research. Below, you can also find my publications.
Gravity may be the weakest of the fundamental forces, but it is the one that rules the evolution and fate of the universe.
Our standard theory to explain the phenomenon of gravity is General Relativity (GR). This beautiful theory was originally proposed in 1915 by Einstein and it describes gravity as the geometry of spacetime. Before this, gravity was best described by the Newtonian universal law of gravitation. This law was able to describe phenomena in our daily life (like apples falling) and also the motion of planets around the Sun. However, the validity of this law is limited. For instance, the orbit of Mercury cannot be described in full detail with Newtonian gravity. It’s not a coincidence that it is Mercury’s orbit which it struggles to explain. This is the planet closest to the Sun, and therefore the one which experiences the strongest gravity.
One of the early successes of Einstein’s GR was to solve the problem of Mercury’s orbit. GR extended the domain of validity of Newton’s gravity, as is illustrated on the right.
After more than a 100 years of physicists developing GR, we are now in a position where we might be in need for an alternative theory which extends further the domain of validity of GR. Problems like the nature of dark energy and dark matter might remind oneself of Mercury’s orbit, and seem to suggest that something else is needed to describe gravity in those regimes. In particular, the regime of large distances, where a mysterious cosmological constant is needed to describe the cosmological evolution of the universe, and the strong gravity regime, where GR has not been fully tested yet, are two scenarios where gravity could be modified from GR.
One of the most awesome predictions of General Relativity is that spacetime itself can behave as a wave.
The last decade has seen the rise of gravitational wave science. In less than 10 years, gravitational waves (GWs) have upgraded their status from mere theoretical predictions to being routinely observed and used quantitatively. Moreover, the field is promisingly set to keep growing with the planned construction of land and space detectors which will hugely amplify our field of view.
GWs coming from the merging of two compact ojects (like neutron stars or black holes) looks schematically like the diagram on the left, with three main characteristic stages. Of special interest is the last one, known as the ringdown, which corresponds to the short-lived waves emitted just after the merger. Ringdown waves, characterised by the so-called quasinormal modes, contain rich and clean information about the black hole characteristics and the underlying gravitational theory.
The situation then is the following: we have a big family of modified gravity theories predicting different kinds of black holes and GW properties. We also have a continuously increasing number of GW observations which are sensitive to such modifications. Putting the two together is then not only very timely but also one of the most powerful ways to test gravity. The aim of my research is hence to select interesting theories, calculate their corresponding ringdown signals, and confront them with the observations to constrain the theory.
More concretely, I study different types of scalar-tensor theories and their black hole solutions. Via a black hole perturbation theory analysis, I evaluate the stability of such solutions and extract their quasinormal modes. This is done in such a way that one can identify the main parameters controlling deviations from GR and therefore put constrains on them.
