High-energy (low-x) QCD evolution
The LHC data offer many new opportunities to investigate quantum chromodynamics at high energies. The latter regime is particularly interesting theoretically, since it is a regime in which the interacting hadrons appear as dense states of partons, whose dynamics is governed by non-linear evolution equations. In this talk, we will review QCD evolution at small-x in the framework of the simple and elegant formulation provided by the color dipole model, which is able to incorporate both linear evolution and high-density effects.
We will start by explaining the formulation of deep-inelastic scattering observables in the dipole model, and by discussing the simplest relevant evolution equation in this case, the so-called Balitsky-Kovchegov equation. We will then turn to a few observables in proton-nucleus collisions (broadening, di-jets, total multiplicity).
We will show in particular how, for these observables, the event-by-event fluctuations of the parton densities play an essential role in the high-energy regime.
Friday, 20 February 2015, ore 14:30 — Sala Wataghin
Recent Advances in String Phenomenology
String Phenomenology is the study of four-dimensional solutions of string theory, which represents a promising ultra-violet completion of gravitational and particle interactions in ten spacetime dimensions. Many mechanisms have been identified in the past years to derive the foundations of the observed Standard Model of Particle Physics from string theory such as the origin of gauge symmetries, chiral matter and its interactions or, in the context of inflationary cosmology, candidates for scalar fields with suitably flat potentials. One of the current challenges is to understand the implications of the apparent multitude of four-dimensional string solutions, the so-called string landscape.
In this colloquium we will stress that one of the primary goals of string phenomenology is to identify string theoretic mechanisms to understand phenomena which are challenging to explain from the perspective of four-dimensional quantum field theory only. We will review, among other examples, how F-theory model building accepts this challenge in the context of Grand Unified Model building while at the same revealing fascinating connections between particle phenomenology and mathematics. Future directions of string model building will critically depend on the role of supersymmetry in explaining the electroweak hierarchy problem.
Friday, 13 February 2015, ore 14:30 — Sala Wataghin
Superfluidity and propagation of sound in ultracold atomic gases
In this seminar I will discuss recent advances in the theoretical and experimental study of superfluid phenomena in ultra cold atomic gases,
with special focus on the propagation of sound at zero and finite temperature. Both Bose and Fermi gases will be considered and the role of low dimensionality effects will be explicitly discussed.
Wednesday, 28 January 2015, ore 14:30 — Sala Wataghin
Atomic Quantum Simulation of Abelian and non-Abelian Gauge Theories
Gauge theories, which realize symmetries locally in space and time, play an important role in many areas of physics. In elementary particle physics, an Abelian U(1) gauge symmetry governs the electromagnetic interaction between electrons mediated by photons, while a non-Abelian SU(3) gauge symmetry controls the strong interaction between quarks mediated by gluons. In condensed matter physics, gauge symmetries arise, for example, in the description of spin liquids, and in quantum information theory Kitaev's toric code is an Abelian Z(2) gauge theory. The solution of gauge theories is often very complicated, in particular, in the presence of strong interactions, as between quarks and gluons in a dense neutron star or between electrons in a spin liquid. Numerical simulations of such systems on classical computers suffer from very severe sign problems. Quantum simulators are accurately controllable quantum systems that can mimic other quantum systems. They do not suffer from sign problems, because their hardware is intrinsically quantum mechanical. Recently, using ultracold atoms in optical lattices, quantum simulators have been designed for Abelian and non-Abelian gauge theories. Their experimental realization is a challenge for the foreseeable future, which holds the promise to access physical phenomena, as, for example, the evolution of strongly coupled quantum systems in real time, whose understanding has remained beyond reach of the traditional tools of theoretical physics.
Friday, 16 January 2015, ore 14:30 — Sala Wataghin
The quantum mechanical simulation in Materials Science
The pioneering quantum mechanical simulations of solids date back to the years 1975-80. Since then the role of ab initio calculations has been rapidly increasing in many scientific areas and communities, due to decreasing cost of the hardware and availability of computer programs of growing capability and ease of use. The potentialities offered by ab initio simulation techniques in the investigation of the properties of crystalline compounds are illustrated with reference to the CRYSTAL code (www.crystal.unito.it). Basic (the variational basis set, the Hamiltonian, the Density Functional Theory), as well as technical (languages, parallel computing, use of supercomputers) aspects are quickly mentioned. The large variety of crystalline properties that can be evaluated (with various degrees of accuracy), including the elastic, piezoelectric, photoelastic, polarizability tensors, the RAMAN and IR spectra, the equation of state, the effect of pressure and temperature, the charge and momentum distributions, will be illustrated through a few examples.
Friday, 19 December 2014, ore 14:30 — Sala Wataghin
Solar and Geo neutrinos
Neutrino physics continues to be a very active research field, full of open fundamental questions reaching even beyond the SM and towards possible new physics. Solar neutrinos have played a fundamental historical role in the discovery of the phenomenon of neutrino oscillations and thus non-zero neutrino mass. Even today, the study of solar neutrinos provides an important insight both into the neutrino as well as into the stellar and solar physics. Neutrino geoscience is a newly born interdisciplinary science having as its main aim determination of the Earth's radiogenic heat through measurement of antineutrinos released in the decay of long-lived radioactive elements inside the Earth (geoneutrinos). The seminar will cover the status-of-art of the present day solar and geo neutrinos physics, as well as a more detailed review of the recent results from Borexino experiment, 300 ton liquid scintillator detector placed deep underground in the Laboratori Nazionali del Gran Sasso.
Friday, 28 November 2014, ore 14:30 — Sala Wataghin
Constraints on neutrino mass and dark matter coldness from cosmological data
I will present the tightest constraints that have been recently obtained from cosmological data on total neutrino masses and dark matter coldness (e.g. sterile neutrinos or thermal relics). These constraints are both derived from a combination of cosmic microwave background data with a relatively new probe of the large scale structure at high redshift and small scales: the intergalactic medium. In deriving these limits I will make use of hydrodynamical simulations of the large scale
structure. Moreover, I will show how these data could provide useful quantitative measurements of the geometry of the Universe at z~2.
Friday, 21 November 2014, ore 14:00 — Sala Wataghin
Quantum simulation with ultracold atoms
Friday, 7 November 2014, ore 14:30 — Sala Wataghin
Phases of strongly interacting matter
Friday, 24 October 2014, ore 14:30 — Sala Wataghin
Results and Prospects of Antihydrogen Production
Friday, 10 October 2014, ore 14:30 — Sala Wataghin