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Journal Club Seminari 2025
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Seminari Journal Club
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16-10-2025 (aula 72)
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ore 16:00
| Lai Alessandro Leonardo (DOTTORATO IN FISICA) | Probing the Variable Soft Excess in Luminous Quasars: A Two-Corona Approach to PG 1407+265 and RBS 229
Active Galactic Nuclei (AGN) are among the brightest objects in the Universe and provide a unique environment to study accretion onto supermassive black holes. Quasars, in particular, stand out for their high luminosities and cosmological reach, making them powerful probes of both astrophysical processes and the distant Universe.
A key but still poorly understood feature of many AGN is the Soft Excess (SE), an excess of low-energy X-ray emission whose physical origin remains debated. PG 1407+265 represents a particularly intriguing case, as it shows a strongly variable SE extending up to ~3 keV. Together with RBS 229, it has been analyzed using a two-corona Comptonization model, combining optical/UV and X-ray data to disentangle the physical components responsible for the emission. This approach allows us to characterize the warm and hot coronae and to investigate their evolution across different epochs. These properties make PG 1407+265 and RBS 229 valuable laboratories for understanding AGN emission and for exploring the behavior of αOX, a key parameter linking the UV and X-ray emission in quasars and their potential use as cosmological tools.
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ore 16:30
| Ferretti Federico (DOTTORATO IN FISICA) | Tracing the Inner Flow: Variability and QPOs in Black-Hole X-ray Binaries
Black-hole X-ray binaries (BHXRBs) represent ideal laboratories to study accretion and ejection processes under extreme gravity. Their emission, variable over a wide range of timescales, reveals a tight connection between the accretion flow and relativistic outflows. X-ray timing studies have shown that quasi-periodic oscillations (QPOs) are a key signature of the inner accretion flow dynamics. These features, observed across different spectral states, provide crucial constraints on the geometry and physical mechanisms at play close to the event horizon. In this presentation I will review the main phenomenology of QPOs in BHXRBs, discussing their classification, observational properties, and the leading models proposed to explain their origin
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29-09-2025 (aula F - V della Vasca Navale n. 84)
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ore 14:30
| Carducci Marco (DOTTORATO IN FISICA) | Introduzione alla fisica modulare
Durante l'evoluzione della stringa, questa spanna il cosiddetto "worldsheet" bidimensionale. Data la simmetria di Weyl, questo ci porta allo studio della teoria conforme ed i suoi generatori di Virasoro. La topologia della stringa permette l'esistenza di due varianti: stringa aperta o stringa chiusa. Un loop chiuso della stringa chiusa ci restituisce la funzione di partizione che gode della cosidetta simmetria modulare. Questa, a seguito del paper seminale di Ferruccio, professore a Padova, è diventata di interesse anche nell'ambito della fenomenologia.
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ore 15:00
| Fiorentino Vincenzo (DOTTORATO IN FISICA) | The QCD axion: astrophysical bounds and finite density effects
Providing an elegant solution to the strong CP problem, and representing a promising candidate for cold dark matter, the QCD axion is one of the best motivated light BSM particles. For this reason, the experimental effort in the search for the axion has increased drastically in recent times, with new experimental proposals like IAXO at DESY, and FLASH at the INFN. This makes it necessary to provide highly precise and reliable bounds on the axion parameter space. In this talk I will give an introduction to the supernova axion bound, focusing in particular on the role of finite density corrections, which are important in the supernova and have been neglected in the past. Additionally, I will describe how the so-called nucleophobic axion models, for which the supernova bound gets sizeably relaxed, survive finite density effects. Finally, I will provide some insight on more recent developments.
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ore 16:00
| Rettaroli Mirko (DOTTORATO IN FISICA) | Viable fit to neutrino observables in possible U(2) flavor models
The explanation of neutrino masses and mixing still represents one of the open questions of the so-called “SM flavor puzzle” today. The purpose of my work is to provide a possible explanation of this problem, introducing an extension of the Standard Model based on a continuous U(2) flavor symmetry (which is locally isomorphic to SU(2) x U(1)), indicated as U(2)F . This symmetry is spontaneously broken by the VEVs of two scalar fields, called flavons. Since the flavon VEVs depend on two small parameters, all hierarchies in fermion masses and mixings arise from powers of these small order parameters.
Assuming that neutrinos are Majorana particles and that the light neutrinos take mass via the type-I see-saw mechanism, we can obtain a list of possible structures for the neutrino mass matrix (which we call patterns), depending on the choice of the U(2)F quantum numbers for the three RH neutrino representations.
After a numerical fit of these matrices to the neutrino observables, we obtain 13 viable patterns, which provide us interesting predictions on neutrino observables, such as the effective electron neutrino mass and the effective Majorana neutrino mass, and also on BSM phenomena such as LFV decays.
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