Research

My activity spans over three main thematic areas of research :

nuclear-physics properties of neutron stars (NS), and their impact on the observability of NSs ;
properties of dense QCD matter in NSs and phase transitions taking place in their interiors ;
gravitational-wave emission from single NSs and their impact on constraining their properties.

The nuclear matter equation of state is the fundamental input for building models of neutron stars according

to the Einstein's general theory of relativity. In fact typical properties like masses and radii depend strongly on the equation of state at densities 8-10 times larger than the nuclear matter saturation density.

The most important contribution I have given in this field is the derivation, in the hadronic sector, of a fully microscopic equation of state in the framework of a microscopic quantum many-body theory, the Brueckner-Hartree-Fock approach, with the explicit inclusion of hyperonic degrees of freedom. A complete set of calculations of the equation of state is now available in tabular form, both at zero and finite temperature. Those are widely used by other scientific groups as input for the numerical simulations of, e.g., compact stars merging and core-collapse supernova explosions.

The investigation of the high density and low temperature region of the phase- boundary between hadronic matter and the quark-gluon plasma is currently a strongly debated problem in the theoretical community, and I have given in this field an essential contribution. Indeed, I have shown that the hadron-quark phase transition in NSs limits the value of the maximum mass to about 2.0 solar masses, thus predicting that the observation of a more massive NS gives direct access to the quark matter EoS which has to be strongly repulsive.

The recent detection of gravitational waves in 2015 opened a new astronomical window to the Universe, and Neutron Stars play a key role in this respect, having the potential of being extremely prolific gravitational emitters in terms of expected detection rates, and possibly the only ones with an expected electromagnetic counterpart. Combined with new data coming from X-ray satellites and radiotelescopes we are now offered a unique possibility to expand our knowledge of dense matter. The GW170817 merger event has allowed to put constraints on the NS radii through the tidal polarizability, measured by the Advanced LIGO-Virgo collaboration.

GW170817 This has produced observational limits, which are complementary with those from nuclear structure and heavy-ion collisions. The theoretical activities illustrated above are the main themes of the European Action MPNS COST Action CA16214, named PHAROS, “The multi-messenger physics and astrophysics of neutron stars”, which addresses nuclear/particle physics aspects, observations, and astrophysics ,.