Ciclo di Conferenze dei corsi di Laurea in Fisica del Dipartimento di Matematica e Fisica
Edizione 2022
Miguel Onorato
Università di Torino, Dipartimento di Fisica
Thermalization in one-dimensional anharmonic chains: the Wave Turbulence approach
Link identifier #identifier__110970-1Locandina – 18 gennaio 2022, ore 15:00 online e Aula A
In the early fifties in Los Alamos E. Fermi in collaboration with J. Pasta, S. Ulam and M. Tsingou investigated a one-dimensional chain of equal masses connected by a weakly nonlinear spring. The key question was related to the understanding of the phenomenon of conduction in solids; in particular, their goal was the estimation of the relaxation time scale needed for the system to reach equipartition of energy among the Fourier modes. They approached the problem numerically using the MANIAC I computer; however, the system did not thermalize and they observed a recurrence to the initial state (this is known as the FPUT-recurrence). This unexpected result has led to the development of modern nonlinear physics (discovery of solitons and integrability). In this seminar, I will give a brief historical overview of the subject and present new results on the problem of thermalization based on the Wave Turbulence Theory.
Emanuele A. Bagnaschi
CERN
Dark matterat the crossroads
Link identifier #identifier__157664-2Locandina – 1 marzo 2022, ore 14:30 online
Understanding the nature of dark matter is one of the most important challenges that the particle physics community is currently facing. In this colloquium we will present the main dark matter candidates, their theoretical backgrounds and the current status of the experimental searches. We will especially focus on the complementarity between direct/indirect searches and collider experiments.
Luca Di Luzio
Università di Padova e INFN Sezione di Padova
Particle Recepies for Axion Hunters
Link identifier #identifier__58837-3Locandina – 3 maggio 2022, ore 15:00 online
Four decades after its prediction the QCD axion remains the most compelling solution to the strong CP problem and a well motivated dark matter candidate, inspiring several ultrasensitive experiments based on axion-photon mixing. After reviewing the axion solution of the strong CP problem and the experimental landscape of axion searches, I will focus on some recent developments in axion model building suggesting that the QCD axion parameter space is much larger than what traditionally thought. The implications for astrophysical limits and current experiments will be discussed as well.
Roberta Citro
Dipartimento di Fisica “E.R. Caianiello” e CNR Spin, Università degli Studi di Salerno
Models and novel platforms for topological superconductivity
Link identifier #identifier__121076-4Locandina – 5 luglio 2022, ore 15:00 online
In this talk I will first review the properties of toy-models for topological superconductivity, the Kitaev chain and its generalizations. After discussing the topological phase diagram of the isolated system, using a scattering technique within the Bogoliubov–de Gennes formulation, I will discuss the differential conductance properties as a function of all relevant model parameters. The relevant problem of implementing local spectroscopic measurements to characterize the Majorana fermions useful in quantum technologies is also addressed. We will also show how topological protection can be lost when the quantum states of an initially isolated topological system are hybridized with those of the external reservoirs. Finally, I will present a novel platform for topological superconductivity based on 2DEGs at LAO/STO interface. Here the interplay of spin-orbit interaction and intrinsic superconductivity may induce a topological phase transition in an applied magnetic field with strong orbital character. The conclusions will address the design of various nanowire-based mesoscopic devices for topological computation.
Andrea Chiavassa
Università di Torino
L’esperimento SWGO: un apparato per la ricerca di sorgenti di fotoni tra 100 GeV e 10 PeV nell’emisfero Sud
Link identifier #identifier__83718-5Locandina – 27 settembre 2022, ore 15:00 online
I recenti risultati ottenuti dall’esperimento LHAASO hanno dimostrato che nel piano galattico si trovano sorgenti di fotoni di energia superiore ai 100 TeV, questo apre la strada all’astronomia gamma a queste energie. In questo quadro la situazione sperimentale vede in questo momento in funzione esclusivamente degli osservatori posti nell’emisfero Nord (LHAASO, HAWC e TIBET-ASγ) è quindi evidente come manchi un osservatorio posto nell’emisfero Sud con il quale osservare il centro galattico.
A energie superiori a 100 TeV la tecnica per osservare queste sorgenti si utilizzano apparati che rivelano sciami estesi atmosferici e che devono essere in grado di separare eventi originati da fotoni dal fondo dovuto agli sciami adronici (essenzialmente generati da protoni). In questo quadro sperimentale si inserisce la collaborazione SWGO, che sta preparando il disegno di un siffatto osservatorio da realizzare nell’emisfero Sud. La collaborazione si è data come obbiettivo quello di progettare un esperimento che operi tra 100 GeV e 10 PeV, che osservi il centro galattico e che sia in grado di operare una buona reiezione del fondo adronico. Questo porta subito alcune conseguenze: l’apparato dovrà essere localizzato tra -10 e -30 gradi di latitudine Sud e dovrà essere realizzato a una quota superiore ai 4500 m s.l.m. La collaborazione ha inoltre scelto come “baseline” la tecnica di rivelazione dei cherenkov ad acqua (essendo però aperta a proposte diverse).
In questo seminario illustrerò le prospettive dell’esperimento SWGO, lo stato della proposta e il contributo dei gruppi italiani che attualmente vi partecipano.
Giorgio Matt
Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre
First results from the Imaging X-ray Polarimetry Explorer
Link identifier #identifier__29925-6Locandina – 4 ottobre 2022, ore 14:30 online
The Imaging X-ray Polarimetry Explorer (IXPE), a NASA/ASI mission, is the first satellite dedicated to study the polarization of cosmic sources in the X-ray band. Launched in December 2021, it is already providing several interesting – and in some cases unexpected – results on many different classes of astrophysical objects. In this talk, the mission will be described and the most important results highlighted.
Renato Torre
European Lab. for Non-Linear Spectroscopy (LENS) e Dipartimento di Fisica ed Astronomia, Università degli Studi di Firenze
From liquid water to biological water: dynamics by ultrafast spectroscopy
Link identifier #identifier__66086-7Locandina – 23 novembre 2022, ore 15:00 online
The proprieties of water are of paramount relevance for matter research, bio-science and many technological applications. The water dynamics typically develops over very fast scale of the order of a few picoseconds, this makes it quite difficult to be investigated by usual experiments. The laser spectroscopy, based on femtosecond pulse, enables accurate measurement of structural and vibrational water dynamics with an unprecedented data quality.
In the talk I will introduce some non-linear time-resolved spectroscopic techniques developed by our research group at LENS; In particular, I will focus on the Optical Kerr Effect tool. Using this spectroscopy, we studied the dynamics of a series of sample in which water is present under different conditions. Starting from the liquid water in supercooled phase, I will compare the experimental results on the dynamics of water when it is confined within silica nanopores or when water hydrates globular proteins at increasing concentration.
Federica Ricci
Dipartimento di Matematica e Fisica, Università Roma Tre; Dipartimento di Fisica e Astronomia “Augusto Righi”, ALMA Mater Studiorum Università di Bologna e INAF-OAS Bologna
AGN Molecular outflows at the golden epoch of galaxy evolution
Link identifier #identifier__105929-8Locandina – 6 dicembre 2022, ore 15:00 Aula 108
The standard merger-driven galaxy evolutionary scenario for the formation of massive galaxies predicts a phase of deeply “buried” supermassive black hole growth coexisting with a starburst before feedback phenomena deplete the cold molecular gas reservoir of the galaxy and an optically luminous quasar (QSO) is revealed. Given the relevance of multi-phase outflow phenomena in AGN feedback models, constraining the gas content in high-z AGN with outflows detected in the ionised phase is a compelling hot topic in extragalactic astronomy. We present ALMA observations of the CO(2-1) and CO(5-4) emissions in two X-ray selected luminous obscured QSOs at z~1.5, adding a missing piece to the understanding of their outflow properties, these targets being the most extreme and the best characterised so far in the ionised outflow component at such redshift. These two obscured QSOs were selected from the XMM-COSMOS survey and are hosted in remarkably different host galaxies, one being a starburst while the other being a normal MS galaxy. Thanks to ALMA sensitive data, we observe both the indirect evidence of AGN feedback in action, finding a low molecular gas fraction and depletion timescale with respect to samples of inactive galaxies with matched host properties, and the molecular counterpart of the ionised wind, with both blue- and red-shifted velocities exceeding 500 km/s and mass outflow rate up to ~2500 Msun/year. Complementing the ALMA submm observations with optical rest frame data, we investigate how the molecular and ionised mass outflow rate correlate with star formation rate, galaxy stellar mass and the AGN luminosity, by assembling the largest (x3 than in previous works) sample of AGN at high redshift (z>1).