On the origin of the chemical elements: from the Big Bang to Neutron Star Mergers
Our understanding of the origin of the chemical elements requires a combination of knowledge in cosmology and particle physics (for the standard big bang model), astronomy and astrophysics (observation of stellar spectra, stellar evolution), and nuclear physics. An overview of the present understanding of the processes responsible for the nucleosynthesis of the elements in the primordial as well as in the evolved universe will be presented, with particular reference to the nuclear physics aspects (experimental and theoretical).
The synthesis of the first few light nuclear species took place shortly (within a few minutes) after the big bang. Particular attention will be devoted to the open questions on the big-bang nucleosynthesis, including the cosmological lithium abundance problem, in relation to the recent results of the experiments performed at the neutron time-of-flight facility (n_TOF) at CERN.
Except for the first three, H, He and Li, all the other elements are synthesized in stars, during various phases of their evolution, including final stages such as supernovae explosions and/or merging of binary systems. In particular, all the elements heavier than iron are formed by a slow neutron capture mechanism (the s-process) and by a rapid neutron capture process (r-process). A full understanding of these two mechanisms, postulated 60 years ago by the pioneering work of B2FH, allows for a direct comparison of the expected and observed abundances of the chemical elements present in the observed universe.
[B2FH] E. Margaret Burbidge, G. R. Burbidge, William A. Fowler, and F. Hoyle, "Synthesis of the Elements in Stars", Rev. Mod. Phys. 29, 547 (1 October 1957)
Friday, 1 February 2019, ore 14:30 — Sala Wataghin
The discovery of a large number of extrasolar planets has demonstrated that our own system is not "typical". Exo-planetary systems can be very different from our own, and diverse from each other. Understanding this diversity is a major goal of modern planetary science. The formation of planetary systems is not fully understood, but major advances have been obtained in the last 10 years. New concepts have been proposed, such as the streaming instability for the formation of planetesimals and pebble accretion for the formation of protoplanets. It is also now clear that planets forming in the protoplanetary disks have to migrate during their accretion, if their mass exceeds a few times the mass of Mars. Accretion and dynamical evolution are therefore very coupled processes. This leads to complex evolutions, very sensitive to initial conditions and fortuitous events, that are the key to understand the observed diversity of planetary systems. The early formation of Jupiter and its limited migration due to the formation of Saturn are two fundamental ingredients that determined the basic structure of the Solar System. The lack of early formation of giant planets typically leads to the formation of super-Earth planets on short period orbits. There is also evidence that the vast majority of planetary systems become unstable after the removal of the protoplanetary disk. The effects of this instability are very different depending on the masses of the planets involved. Our Solar System also experienced a global instability, but fortuitously our giant planets did not develop large orbital eccentricities.
Thursday, 24 January 2019, ore 15:00 — Aula Magna "Tullio Regge"
Exploring fundamental physics with gravitational waves
With the first direct observation of gravitational waves, a new era in astrophysics has begun. In this seminar, addressed to a broad audience, I will discuss some aspects of gravitational wave physics closely related to fundamental questions - from both the phenomenological and theoretical viewpoint - in our journey towards a deeper understanding of the wonders of Nature.
Friday, 18 January 2019, ore 14:30 — Sala Wataghin
The flow of time and temporal experience
One of the things that our ordinary experience seems to tell us is that time passes. How seriously we should take this very basic belief is not a trivial question. It depends both on what the characterizing features of temporal experience are, and on what structural aspects time has. Both issues are discussed in contemporary philosophy of time, and bear interesting connections with empirical results in psychology and physics. I my talk I will present some of the main views on the market and defend and account which is anti-realist with respect to time flow, but in which our experience does not turn out to be illusory.
Friday, 14 December 2018, ore 14:30 — Sala Wataghin
Nature 1 - 1 LHC (half-time)
We'll discuss fundamentals of science as applied to fundamental
science in high-energy particle physics at the LHC. After a stroll through
the garden of the LHC's main accomplishment, we'll wander through a dark
forest of what is beyond until we make out the light from the prairie of
high-precision.
Friday, 23 November 2018, ore 14:30 — Aula C
New Developments in Cosmic Microwave Background Lensing
I shall give an introduction to CMB lensing. Then I shall discuss new developments where lensing effects are taken into account at second and third order, including so called ’post-Born’ contributions. Especially, I shall show that beyond leading order, CMB polarisation acquires a rotation due to lensing. This result is still debated in the literature and I shall present the arguments as well as a (tentative) resolution.
Monday, 05 November 2018, ore 14:30 — Aula C
Superinsulators: a new state of matter with hadrons made of Cooper pairs
I will present the physics of superinsulators, a state of matter dual to superconductors. Superinsulation is due to a condensate of magnetic monopoles in which electric fields are squeezed into thin strings dual to Abrikosov vortices, confining elementary Cooper pairs into neutral mesons, preventing any charge transport and thereby causing an infinite resistance. Superinsulators are thus a single-colour version of QCD and provide the first concrete experimental realization of (non-critical) string theory and a simple tabletop setting for experiments on confinement and asymptotic freedom. I will describe both theory and experiments on superinsulators and conclude with some potential technological applications.
Friday, 26 October 2018, ore 14:30 — Sala Wataghin
A Quantum Universe before the Big Bang(s)
The fundamental role of quantum physics in modern cosmology entails a deep revision of our traditional ideas about the Big Bang and the beginning of time.
Friday, 5 October 2018, ore 14:30 — Aula C