Journal Club

(DOTTORATO IN FISICA)

X-ray study of optically selected dual AGN

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Galaxy merging phenomena at pc−tens of kpc scales are subjects of interest in modern Astrophysics, since they could cause the triggering of the Active Galactic Nuclei (AGNs) and the formation of Super Massive Black Holes (SMBHs) at the center of the galaxies, as several studies suggest. When two interacting galaxies host two AGNs (one each), we refer to them as dual AGN. However, multi-waveband observations are needed in order to properly identify and characterize dual AGNsystems. X-rays are a powerful method with which we can detect AGNs and study their properties, such as the absorption caused by a dusty material which obscures the inner regions of the AGN. Here we present the X-ray study of 28 dual AGN candidates optically selected or via a double-peaked [OIII]λ5007Å line profile, or via the photometrically resolved image of the two nuclei. By performing a detailed spectral analysis of 17 sources of our sample, we find that ∼70%of the sources seems to be in an absorption regime (Hydrogen column density nH > 1022cm−2). This absorption regime is confirmed by several diagnostics, such as the L[OIII]−Lintr X (2−10keV) and the FX(2−10keV)/νFν(22µm) relations, the latter also highlighting a fraction of ∼ 20% of Compton-Thick (nH > 1024 cm−2) sources. These results suggest that the fraction of obscured sources is significantly higher when looking at dual systems, with respect to isolated AGN (where the fraction of absorbed sources is ∼ 45%).

 

 

(DOTTORATO IN FISICA)

A simplest flavor model for leptons: the revival of modular S3

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In the recent past, substantial effort has been devoted to exploring flavor symmetries to understand neutrino masses and mixing. However, traditional flavor symmetry models proved to be quite unsatisfactory. In 2017, a new 'bottom-up' approach based on modular invariance was suggested, wherein the Yukawa couplings of the Standard Model become modular forms of level N. Within this framework, we addressed the following question: is it possible to employ the lowest level and most minimal modular group S3 to construct predictive lepton mass models? As demonstrated in our work, the answer is affirmative if we assume a certain set of guiding principles that fully exploit modular invariance. Among other observables, the model is able to predict a normal ordering of neutrino masses and a Dirac CP-phase near maximal violation.

 

 

(DOTTORATO IN FISICA)

The DISSHARTA - 2 Experiment at DAONE

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QCD is the theory that describes the strong interaction. In this theory the mediators (gluons) are self-interacting. This peculiarity reflects in a particular running of the coupling constant as a function of the energy scale: at high momentum transfer (Q²) the coupling of the strong interaction (αs) is decreasing, and the quarks and gluons behave almost as free particles enabling the treatment of QCD by using the perturbation theory. At low Q² below energies of ∼1 GeV), on the other hand, αs diverges making QCD non-treatable perturbatively. For this reason, phenomenological models are an appropriate method to understand how hadrons interact at low energy.
In this framework, the exotic atoms with hadrons (atoms in which a negatively charged hadron replaces an electron and bounds to a nucleus) represent a unique experimental tool to test and provide inputs to phenomenological models on strong interactions at threshold.
Particularly, the experimental studies on kaonic atoms play a key role since they can directly probe the non-perturbative regime of the QCD in the strangeness sector.
The DAΦΝE collider at INFN-LNF represents an ideal machine to perform kaonic atoms measurements, thanks to the low-energetic and almost monochromatic beam of kaons generated.
The precise measurement of the shift and the width induced on the 1s level of kaonic hydrogen, two important observables strictly liked to the iso-scalar and iso-vector antikaon-nucleon scattering lenghts, was achieved by the SIDDHARTA experiment. To fully disentangle the iso-scalar and iso-vector scattering lengths, the measurement of kaonic deuterium is necessary as well.
The SIDDHARTA-2 experiment, now taking data at the DAΦΝE collider, aims to fulfill the need of this measurement, providing important constraints to models on low-energy strong interactions. Furthermore, the collaboration is exploring the possibility to perform future kaonic atoms experiments crucial for a deeper understanding of the kaon-nucleons interactions in function of the nuclear density, developing X-ray detector systems beyond the current state-of-art.
The collaboration also aims to solve the kaon mass puzzle, that alters many measurements in particle physics.