Titolo
Un nettare per curare l’Alzheimer: la fisica nucleare in soccorso
all’invecchiamento globale.

Relatori
N.Protti, V.Pascali

High-order harmonics are generated from the interaction of intense femtosecond laser pulses with noble gases. Recently, high-order Harmonic Generation (HHG) led to the realization of table-top sources of coherent XUV and Soft-X Ray radiation. With these sources, ultrafast spectroscopy can be performed with extreme temporal resolutions, down to the attosecond regime (1 as = 10^-18 s), and with the site and chemical selectivity. These features grant access to purely electronic dynamics in molecules and solids and fundamental processes of light-matter interaction. Furthermore, HHG has been successfully used as a spectroscopic tool in the gas phase and condensed matter, allowing the study of electron dynamics in a cation following sudden ionization, all-optical band structure reconstruction, and berry phase retrieval. These findings demonstrate the flexibility and potentiality of this technique.

In this colloquium, I will introduce the principle of high-order harmonic generation as a source of XUV radiation and its application for ultrafast XUV spectroscopy and high-order harmonic spectroscopy. I will also report on the most recent developments in ultrafast XUV spectroscopy based on HHG in the Udyni labs [1] at CNR-IFN.

I will describe our recent developments in efficient XUV generation in microfluidic devices fabricated by femtosecond laser irradiation followed by chemical etching [2]. With this approach, we were able to control the harmonic generation process in the gas on the micro-meter scale with high flexibility, enabling a high photon flux and phase matching on broadband harmonics up to 200 eV. This source is part of a new beamline for transient absorption/reflectivity measurements in molecules and solids. I will also describe the beamline developed for HHG spectroscopy in solids available at CNR-IFN and report on preliminary results in dielectrics and semiconductors.

[1] www.udyni.eu

[2] A. G. Ciriolo et al., J. Phys. Photonics 2, 024005 (2020); https://doi.org/10.1088/2515-7647/ab7d81

[3] A. G. Ciriolo et al., APL Photonics 7, 110801 (2022); https://doi.org/10.1063/5.0118199

Course contents:

1. Metals and free electron excitations (plasmons); localised and propagating surface plasmons, surface plasmon-polaritons (SPPs).

2. Graphene: crystal structure, chemical bonds, electron energy spectrum and electronic properties; brief overview of other properties and applications.

3. SPPs in graphene-based structures: dispersion relation, excitation methods; working principles of some sensing and optoelectronic devices.

4. Brief introduction to the non-linear optical properties of graphene.

5. (depending on time availability) Nearly 2D semiconductors, the transition metal dichalcogenides (TMDs): electronic properties, excitons, selected applications.

Nanostructures, such a quantum dots or nanoparticles, made of three-dimensional
topological insulators (3DTIs) [1-5] have been recently attracting increasing interest,
especially for their optical properties. We present results for the energy spectrum,
the surface states and the dipole matrix elements for optical transitions with in-
plane polarisation of 3DTI nanowires of finite height L and radius R. We first derive
an effective 2D Hamiltonian by exploiting the cylindrical symmetry of the problem.
We develop two approaches: The first one is an exact numerical tight-binding model
obtained by discretising the Hamiltonian; The second one, which allows us to obtain
analytical results, is an approximated model based on a large-R expansion and on
an effective boundary condition to account for the finite height of the nanowire.
We find that the agreement between the two models, as far as eigenenergies and
eigenfunctions are concerned, is excellent for the lowest absolute value of the
longitudinal component of the angular momentum. Finally, we derive analytical
expressions for the dipole matrix elements by first considering the lateral surface
alone and the bases alone, and then for the whole nanowire. In particular, we focus
on the two limiting cases of tall and squat nanowires. The latter case is compared
with the numerical results finding a good agreement

The Beam Dump eXperiment is a state of the art, modern beam dump experiment approved by JLab PAC with maximum scientific rate. BDX aims to detect light dark matter particles in the interaction of the intense 11 GeV CEBAF electron beam with the dump of experimental Hall-A. In this contribution I will show the genesis of the experiment and its evolution  toward a pilot run we just concluded at Jlab (BDX-MINI). The physics case, as well as the experimental technique (simulation framework, detector design and prototyping), will be review and discussed.
 

Many astrophysical observations as well as anomalies in processes involving electromagnetic currents (e.g. the muon anomalous magnetic moment) could be reconciled assuming the existence of a new kind of matter, not directly interacting with light, called Dark Matter (DM). While gravitational effects of DM are quite well established, despite the tremendous efforts being devoted to reveal the nature of DM in terms of new elementary particles, no clear results have been obtained so far. Many experimental efforts are dedicated to direct detection of galactic DM, as well as to study the indirect effects of its presence. Due to the lack of results by ‘traditional’ DM searches, in the last few years the experimental activity extended to search for hints of DM produced at accelerators. Technological advances allow nowadays running high intensity  beams of moderate energy well suited for these studies. According to some theories beyond the Standard Model (SM) Light Dark Matter (LDM ) (1-1000 MeV) can interact with SM matter via a new force, mediated by a heavy vector boson called A’ or ‘heavy photon’. Depending on the relative masses of the A’ and the DM particles, the A’ can decay to SM particles (‘visible’ decay) and/or to light DM states (‘invisible’ decay). In this talk, I will give an overview of the LDM physics, focusing on the current experimental effort in the field.
 

We will discuss some newly found solutions to the full massless semiclassical Einstein equation (SCE) in a cosmological setting (Λ=0).

After a short introduction to the relevant notions we present the SCE in a particular shape which allows for the construction of a Minkowski-vacuum-like states. In this setting, solving the SCE breaks down into solving a certain ODE which can be approached numerically and, at least generically, we obtain solutions that well fit physical expectations. Moreover, these solutions indicate dark energy as a quantum effect on cosmological metrics and, since in our model m=Λ=0, this may not be traced back to the usual, obvious dark-energy/cosmological constant effect of a quantum field. Also we will shortly discuss some more physical problems that can be solved by our model. To close the talk, we will briefly speak about de Sitter solutions of the model and thereby foreshadow another talk taking place at the University of Genova later in the week.

In this talk I will give a description of the boundary structure of 3 + 1-dimensional gravity (in the Palatini–Cartan formalism) coupled to to gauge (Yang–Mills) and matter (scalar and spinorial) fields through the use of the Kijowski–Tulczijew construction. In particular, the reduced phase space is obtained as the reduction of a symplectic space by some first class constraints. Furthermore, if time permits I will give a cohomological description (BFV) of it. This is a joint work with A. S. Cattaneo and F. Fila-Robattino.

In this set of lectures we consider the different types of interpretations that have been considered for physical theories in general, and sketch out a variety of interpretations of quantum mechanics and their problems, including “textbook” quantum mechanics, issues of local causality and signal locality, Copenhagen quantum mechanics, operationalist quantum mechanics, some issues with hidden variable theories in general, Bohm-deBroglie quantum mechanics, consistent histories quantum mechanics, many worlds quantum mechanics, Qbism, and perhaps a few more (or a few less!) as time permits.