PER2A0P2S3 è un ciclo di seminari su vari temi di Fisica,
di Fisica-Matematica e più in generale vertenti su argomenti che hanno la Fisica come scienza di riferimento.
Si svolgono nella sede di via Alessandro Pascoli del
Dipartimento di Fisica e Geologia,
in orario pomeridiano, tipicamente di mercoledì o giovedì. A chiusura di ogni seminario il Dipartimento
offre un bachetto di frutta.
Tutti sono invitati a proporre seminari.
Mercoledì 13 dicembre
Ore 15:00 - Aula A
How the observed receding motion of the nearby universe is caused by negative charges retained by galaxy clusters
A new idea explaining the expansion of the universe is presented and debated. The receding motion of nearby universe within 1026 meters has never been explained with well assessed Physics Laws. According to a recent, complete study anchored to many empirical data, any spiral galaxies retain permanent electrostatic fields due to the motion of cosmic rays. Spiral galaxies and other galaxy types as well, experience multiple and variegated interactions in galaxy clusters as attested by X-ray, radio and optical data, thereby loosing the halo of positively charged cosmic nuclei, leaving negative charges of some 1033-1034 Coulomb in cluster cores. Negative charges are also suggested by upper limits of diffuse gamma-ray fluxes in galaxy clusters. Along this line of arguments velocities of galaxy clusters from the Earth caused by electrostatic fields generated by cosmic rays are calculated. The chief result, obtained in several pertinent conditions related to the expansion of the nearby universe, is that cluster velocities increase as cluster distances from the Earth augment.
Martedì 14 novembre
Ore 15:00 - Aula C
Recent results and plans of the NA64 experiment
at the CERN SPS
Thermal dark matter models with particle masses below the electroweak scale can provide an explanation for the observed relic dark matter density. This would imply the existence of a new feeble interaction between the dark and ordinary matter. The main purpose of the NA64 experiment is a search for sub-GeV dark matter production using the method of missing energy signature. The searches are performed at the H4 beam line at the CERN SPS. This beam is mainly designed to provide 100 GeV electron beam. The analysed statistics corresponds to 9.37 ×1011 electrons on target (EOT) collected during 2016-2022 runs. The analysis of this statistics allowed to probe for the first time the well motivated region of parameter space of benchmark thermal scalar and fermionic dark matter models. Additional statistics of about 6 ×1011 was collected in the 2023 run. In addition to the main 100 GeV electron-beam measurement, NA64 is also developing a positron-beam program with several runs at different energies, to explore the ~ 100 MeV mediator mass range by exploiting LDM production via resonant e+e- annihilation. This search is also supported by a dedicated ERC project, the POsitron resonant annihilation into darK mattER (POKER) project, lead by INFN-Genova. An early test run already demonstrated the feasibility of the new technique, allowing to set competitive new limits in a limited mass region despite the much lower accumulated statistics. The variant of the NA64 detector for the searches of DM in the muon beam, called NA64mu, is also developed. It uses part of subdetectors of NA64e and a number of additional subdetectors. The purpose is to search for DM coupled only to second and third generations of leptons, suggested to explain the (g-2) anomaly and to improve sensitivity in the region of mediator masses above ~300 MeV. NA64 performed and plans also a number other searches, such as the search for ALP coupled to gammas, search for X boson decaying to electrons, search of DM in the hadron beams, search for mu-tau conversion.
Giovedì 26 ottobre
Ore 15:00 - Aula B
Sincrotroni acceleratori di sviluppo
Il progetto nei Grandi Caraibi
Si presenta lo stato del progetto di un secondo sincrotrone latinoamericano nei Grandi Caraibi, nel quadro della problematica scientifica, economica e sociale della regione.
Giovedì 19 ottobre
Ore 15:00 - Aula B
At the heart of the matter
The proton is the most common particle in nature. However mysteries associated to its size,
composition, and internal structure still subsist. A new view of the charge and magnetic
distributions inside the proton (in terms of quantities called "form factors") is emerging
since the beginning of this millenium, due to the enormous progress in particle accelerators,
detectors and polarimetry. In particular, elastic electron proton scattering and electron-positron
annihilation into a proton-antiproton pair give a description of the proton in the four dimensions,
space and time. We will describe and interprete the recent results in terms of a model that calls for
a dynamical picture of the proton, where different gluon and quark states may coexist: a three-quark
state, a quark-diquark configuration as well as an inner region of quantum vacuum.
A short video will be shown to illustrate these findings.
Mercoledì 4 ottobre
Ore 15:00 - Aula A
Decoding the Lives of Red Giant Stars: New Spectroscopic Clues
Stars in their late evolutionary stages undergo many changes as their interior engines use up nuclear fuel and prepare to die violently as supernovae or meekly as white dwarfs. These aging red giant stars stars execute major movement in the Hertzprung-Russell diagram, and they pulsate on short and long timescales. Their surface light element abundances (e.g. CNO) change in expected ways but sometimes also in baffling ways. In particular, for a few decades we have struggled to understand the curious appearance of extremely large lithium abundances in about 1% of red giants. More recently, we have discovered that many lithium-rich red giants have extremely strong helium 10830A absorption lines, which suggests abnormally active chromospheres of these stars. Additionally, both the Li and He spectroscopic features often are accompanied by large stellar rotational velocities. In this talk I will explore the correlations among these spectroscopic features, and try to relate these observational parameters to recent past actions and expected near-future changes in red giants.