My research mainly revolves around neutrinos in astrophysics and cosmology, as well as multi-messenger astrophysics. Below, I provide a glimpse on my work.
I am fascinated by neutrinos! These puzzling elementary particles vastly outnumber all other particles in our universe, except photons. Neutrinos interact very weakly. Three distinct families or “flavors” of neutrinos exist and they oscillate (convert) into each other by flavor mixing.
Spanning an incredibly large energy range, neutrinos are copiously produced in a variety of astrophysical environments, ranging from stars like the Sun to the most extreme astrophysical transients like core-collapse supernovae and neutron star mergers. Many cosmic accelerators, such as gamma-ray bursts or active galactic nuclei, should also produce neutrinos. Owing to their feeble interactions, neutrinos have the extraordinary ability to escape, almost unimpeded, from cosmic sources and carry information on sites not otherwise accessible. If you are curious to know more about neutrinos and their sources, check our review paper (Vitagliano, Tamborra, Raffelt, 2020).
Neutrinos are crucial to the dynamics of the most spectacular events in our galaxy: Core-collapse supernovae (SN). According to the delayed neutrino-driven explosion mechanism, neutrinos provide new energy to the stalled shock wave to trigger the SN explosion. The most recent SN simulations in 3D suggest that neutrinos and gravitational waves carry experimentally detectable imprints of the SN physics. Neutrinos also drive the LESA hydrodynamical instability. LESA consists of an astonishingly large asymmetric emission of electron neutrinos with respect to electron antineutrinos with possible major implications for flavor conversions and nucleosynthesis. Moreover, neutrinos and gravitational waves may be the only detectable probes of black hole forming stellar collapses.
A SN explodes somewhere in the Universe every second. The detection of the cumulative flux of neutrinos from all SNe, the so-called Diffuse Supernova Neutrino Background (DSNB), is now within reach. The DSNB will allow to constrain properties of the SN population, such as the fraction of black-hole forming collapses and the local supernova rate. If you are curious to learn more about the role of neutrinos in SNe, check our review paper on the topic (Mirizzi, Tamborra et al., 2016).
NEUtrino quantum kinetics
Supernovae as well as compact binary mergers are neutrino-dense environments. The forward scattering of neutrinos with each other is not negligible and is responsible for coupling the flavor evolution of neutrinos with different momenta in a non-linear fashion. Recent developments concern the possibility that fast pairwise neutrino conversion occurs, possibly leading to flavor equilibration (see Tamborra & Shalgar, 2020 for a review on the topic). If this conjecture is confirmed, the SN explosion mechanism, the merger disk physics, as well as the synthesis of the heavy elements will be dramatically affected.
Compact Binary Mergers
The massive neutron star (NS) or black hole (BH) accretion disk resulting from NS–NS or NS–BH mergers is dense in neutrinos, similarly to SNe. In compact binary merger remnants, the flux density of electron antineutrinos is larger than the one of electron neutrinos, differently from core-collapse supernovae. Flavor instabilities could occur everywhere above the neutrino emitting surfaces in mergers because of the merger geometry and the natural excess of electron antineutrinos. As a consequence, an enhancement of the lanthanide mass fraction is expected. Our findings hint towards a potentially relevant role of neutrino physics for the modeling of the kilonova lightcurves and the cooling of the accretion disk.
Particle Acceleration & Cosmic Accelerators
The IceCube Neutrino Observatory, a giant neutrino telescope deployed deep in the Antartic ice, routinely detects cosmic neutrinos with PeV energy, the highest energy ever observed. We do not know yet the origin of these neutrinos, although it is clear that they are generated from cosmic accelerators out of our Galaxy.
By employing the most recent electromagnetic data, collected at different wavelengths, we investigate the particle production and acceleration in a range of cosmic accelerators, such as star-forming galaxies, galaxy clusters, supernovae, gamma-ray bursts, and fast blue optical transients. In particular, despite the fact that we only have hundreds of neutrino events, we are already able to constrain the physics of cosmic accelerators by employing multi-messenger constraints.
Physics Beyond the Standard Model in Astrophysical Sources
Neutrinos of astrophysical origin provide a fascinating window into Physics Beyond the Standard Model. For example, if neutrinos convert in keV-mass sterile neutrinos in the SN core, a non-negligible lepton asymmetry generates with possibly major implications on the SN physics. At the same time, a self-consistent treatment of the production of keV-sterile neutrinos in the SN environment leads to very different bounds on the mass-mixing of these particles. Similar conclusions hold for light sterile neutrinos and other scenarios involving New Physics.
The high-energy neutrinos observed by the IceCube Observatory can also carry observable imprints of New Physics occurring within the source or during propagation to Earth. Hence, astrophysical neutrino data already allow to place stringent independent bounds on New Physics.
The Early Universe is dense in neutrinos. Neutrinos are usually assumed to be fully thermalized at the BBN epoch. However, this assumption may be modified (with a non-negligible impact on the observables) because of non-standard physics affecting the neutrino sector and flavor conversion. A sophisticated modeling of the neutrino propagation in the Early Universe is still missing given our superficial understanding of neutrino conversions in dense media, we are working to asses the impact that neutrino physics may have on the cosmological observables.