Exploring the nonthermal Universe with TeV and PeV gamma-rays
The origin of Cosmic Rays (CR), more than 100 years after their discovery, is still considered a “century-old mystery”. Therefore the identification of the astronomical sources responsible for the locally measured fluxes of CRs remains one of the highest priorities of the field. However, the CR studies cannot be reduced merely to this objective. The term ‘cosmic rays’ has broader implications. After matter, radiation and magnetic fields, these relativistic particles constitute the fourth substance of the observable Universe. The localization, identification and exploration of physical conditions and processes in these CR factories, independent of their relative contributions to the ‘CR fog’, is a fundamental issue in its own right. In this context, the Extreme Accelerators - perfectly designed by Nature machines accelerating particles with a rate close to the theoretical
margin are of particular interest. I will discuss the recent progress in this area thanks to the (surprise) discovery of hundreds of gamma-ray sources reported at TeV and PeV energies.
Monday, 20th June 2022, ore 14:30
News from the lattice, Anomalies and the Unitarity Triangle Fit
The Standard Model of particle physics leaves many fundamental questions unanswered, among which, for example, neutrino masses, matter-antimatter asymmetry and the nature of dark matter. Flavour physics (the intensity frontier) is one of the main fields of investigation to unveil the unsolved questions. Several aspects of flavour physics, including the recent experimental ``anomalies” in leptonic decays, are critically reviewed. New results and ideas to improve the accuracy of the theoretical predictions and future developments are discussed.
Friday, 27th May 2022, ore 14:30
The standard view of critical phenomena, such as the liquid-gas critical point or the Curie temperature of a ferromagnet, is through the Renormalization Group. I will describe an alternative – view it as a self-consistent “soup” of interacting fluctuations, governed by tight equations of Conformal Field Theory. This approach is both rigorous and calculable, with unprecedented precision for the critical exponents of the 3D Ising and other models.
Friday, 13th May 2022, ore 14:30
Probing Gravity and Fundamental Physics with Gravitational Waves
In 2015 the LIGO and Virgo Collaborations observed, for the first time, a gravitational wave
passing through the Earth produced by the merger of two black holes. Such an event was a milestone for astrophysics and it provided a remarkable confirmation of the general theory of relativity. Since then, as many as ninety gravitational waves have been observed by the LIGO and Virgo experiments, including signals from binary neutron stars and neutron-star--black-hole binaries. These observations rely on precise theoretical predictions of the relativistic two-body dynamics and gravitational radiation.
After reviewing the synergetic approach that successfully combines analytical and numerical relativity to produce accurate waveform models, I will discuss the most compelling findings from the latest LIGO-Virgo observing run regarding astrophysics, gravity and fundamental physics. I will also highlight the bright future of gravitational-wave astronomy with the opening of new frequency bands on the ground (Einstein-Telescope/Cosmic Explorer) and in space (LISA) in the next decade, and the theoretical challenges and opportunities of developing high-precision waveform models to take full advantage of the discovery potential.
Friday, 01 April 2022, ore 14:30
Neutrino physics: from open questions to physics beyond the Standard Model
One of the most compelling discoveries in particle physics of the past 40 years is that of neutrino oscillations and consequently neutrino masses, marked by the Nobel Prize in Physics in 2015. This is so far the only particle physics evidence that the Standard Model is incomplete and, together dark matter and the baryon asymmetry of the Universe, guides us in the search for the ultimate theory of particles and interactions.
Despite the impressive advance in determining the properties of massive neutrinos, a complete picture is still lacking. In this talk, I will review the current status and will discuss the open questions and the broad experimental programme that will address them by the end of this decade. Going beyond the standard scenario of 3 neutrino mixing, I will also discuss (unconfirmed) anomalies that have emerged in this field and still lack a compelling explanation: from MiniBooNE to reactor neutrino results. I will ask the question if these puzzling results can hint towards a new Standard Model of particle physics at low energies.
Friday, 21 January 2022, ore 14:30
Interpolation and learning with scale dependent kernels
We study the learning properties of nonparametric ridge-less least squares. In particular, we consider the common case of estimators defined by scale dependent (Matern) kernels, and focus on the role scale and smoothness. These estimators interpolate the data and the scale can be shown to control their stability to noise and sampling. Larger scales, corresponding to smoother functions, improve stability with respect to sampling. However, smaller scales, corresponding to more complex functions, improve stability to noise. We will discuss to which extent these results can explain the learning curves observed for large overparameterized models. Our analysis combines, probabilistic results with analytic techniques from interpolation theory.
Friday, 26 November 2021, ore 14:30
A history of some recent attempts to go beyond the standard model
Weak interactions and neutrinos are at the roots of the standard model of elementary particles (SM). Since the seventies, just after the formulation of this theory, physicists have immediately tried to identify its shortcomings, aiming at making it even more complete. A breakthrough came, not from the process pointed out by most theorists - proton decay - but rather from neutrino physics; and it is ironic to note that the role of taking us beyond the frontiers of SM has been played by neutrino oscillations, theoretized before the SM. A very interesting open question in particle physics concerns exactly the nature of neutrino masses, which leads us to the very foundation of the theory of matter and of the SM. Standard cosmology also highlights further limitations of SM and provides us with important information about neutrino masses, but in a manner that is entangled with our understanding of gravity. Some promising directions of development, concerning the long-term perspective of the discussion, are finally mentioned.
Friday, 15 October 2021, ore 14:30