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Journal Club Seminari 2026
Dottorato in Fisica
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27-05-2026 (AULA C- VIA DELLA VASCA NAVALE N. 84)
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ore 15:00
| CIMBOLLI SPAGNESI FLAVIA (DOTTORATO IN FISICA) | Preliminary tests to combine X-ray microtomography and dielectric measurements to assess the radar properties of pure water ice
Two large space missions, ESA's JUICE and NASA's EUROPA Clipper are on their way to reach the icy satellites of Jupiter in the early 2030s. One of the main scope of the missions is to find liquid water below/inside the icy crusts and to assess the habitability conditions of such ocean worlds. Radar sounders, on board these missions, will play a fundamental role in detecting position, depth and composition of the water. However, presently our understanding of the composition and thermal state of such icy crusts are poorly constrained, which makes the detection of liquid water using radio waves very difficult. Therefore, it is of paramount importance to perform systematic measurements of the dielectric properties of a large set of icy materials having different salt composition and temperature, to define the range of penetration of the radar signals in different scenarios and to assess the detectability limit of the water.
To reach this goal, as a first step, it is important to determine the dielectric properties of pure water ice in the frequency range typical of planetary radar sounders (1-100MHz). The scope of this work was to optimize the laboratory procedure to assess such properties, combining x-ray microtomography images with low/high frequency dielectric measurements. The experimental work was initially focused on defining a procedure to produce polycrystalline Ih ice samples, minimizing the presence of defects like air bubbles and cracks, which are known to affect the results of the dielectric measurements. To this goal different samples were prepared using different sample holders and cooling rate, and then analysed qualitatively and quantitatively using microtomography.
Once the best procedure to minimize ice defects was assessed, samples of pure ice were produced in a climatic chamber in two different measuring cells, the microtomography and a dielectric cells, to test the possibility to perform structural analysis and dielectric measurements on the same type of ice. Dielectric measurements were tested using both a capacitive cell connected to an LCR-meter instrument and a coaxial line connected to a VNA. The results of this work confirm that this procedure can be successfully applied to control the integrity of the sample and to assess, at the same time, the dielectric properties of the ice.
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ore 15:40
| TOGNETTI NICOLE (DOTTORATO IN FISICA) | Selection rules for charged lepton and down quarks operators from residual flavour groups
In this work, we investigate the possible phenomenological impact of residual flavor groups in the charged lepton and down quark sector. This extends the idea of a previous work from which we take the ansatz of a cyclic abelian group as responsible for flavor mixing and the formalism required to categorize the flavor structures. The novelty here is the inclusion of down-type quarks in the picture; we work in a GUT-inspired framework where the left-handed leptons and right-handed down quarks are part of the same SU(5) representation.
For each assignment of the flavor group, only a set of flavor structures is allowed, leading to distinctive patterns of processes. All these structures are strictly related to a SMEFT operator; in the literature, one can find analytical expressions for how specific physical processes are affected by the insertion of these higher-dimensional operators. The goal is to invert these expressions and deduce lower bounds on the new physics from the experimental limits of our chosen observables.
Once these bounds are acquired, we can compare them with those obtained in the previous work (where no quarks were included) and use them to establish a compatibility scheme between a certain set of processes and a specific symmetry group and charge assignment. The inclusion of quarks results in a rich phenomenology that includes, but is not restricted to, meson decays in LFV modes and exotic purely hadronic processes.
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