Eventi del Dottorato

Dottorato in Fisica

Journal Club Seminari 2024

22/05/2024   ore 15:00
Towards a Lagrangian Double Copy for Supergravity
In 2008 Bern, Carrasco and Johansson introduced the so-called Double Copy relations, which are correspondences between gravitational and Yang-Mills theories which allow one to compute tree-level n-graviton amplitudes from tree-level n-gluon ones. These relations provided tremendous simplifications in the computations for graviton scattering, thus allowing for a greater insight on (super)gravitational theories. One of the topics of main interest concerning the Double Copy is the search for a possible Lagrangian origin to the relations, i.e. a possible connection between the Lagrangians of Yang-Mills theories with those of gravitational theories which justifies the correspondence found for the amplitudes. In this contribution, we present our strategy for the Double Copy construction of perturbative Lagrangians for gravitational theories by discussing the examples of the free Lagrangians of N=0 Supergravity and of N=1 Supergravity coupled to a chiral multiplet.

Evolution and dust production by AGB stars in Andromeda
The stars evolving through the Asymptotic Giant Branch (AGB) are generally regarded as highly efficient dust
manufactures, owing to the thermodynamic properties of their wind, which prove extremely favourable to
the condensation process of gas molecules into solid grains. In this talk, I will describe the dust and
mineralogy of the dust formed in the surroundings of this class of stars, outlining the role of mass and
metallicity, and the importance of these studies for the characterization of evolved stellar populations in
galaxies. In detail, I will focus on one of the most interesting and well investigated galaxies: Andromeda
(M31). The scope of this study is to analyze the AGB population of M31, in order to obtain a full
characterization of the sources of the progenitors, and the current evolutionary stage and dust production
Estimating the physical properties of the snow cover in the Apennines through GPR and FDR techniques
Data and simulations show a significant reduction in the snow cover extension due to global warming, and this is particularly evident in the Central Italian Apennines (CIA). Due to its high spatial and temporal variability, it is necessary to use satellite data that allow constant and large-scale monitoring of snow cover: in this context, the SMIVIA project aimed to integrate Synthetic Aperture Radar (SAR) data and in situ measurements to characterize snow physical parameters in the CIA region. The aim of this research work is to use geophysical techniques for carrying out in situ measurements of snow cover properties and to characterize the accuracy and precision of the estimates. For this purpose, two electromagnetic techniques are employed: Ground Penetrating Radar (GPR) and Frequency Domain Reflectometry (FDR) via Vector Network Analyzer (VNA). GPR technique, based on the emission of electromagnetic pulses into the snow layer, exploits the dielectric contrasts in the subsurface and provides data on its physical properties and stratigraphy in a non-invasive way. FDR technique uses high-frequency signals that propagates along an open-ended transmission line to estimate dielectric parameters like permittivity and conductivity, that allow to obtain density and water content via empirical relations. The results of the measurements, carried out for two winter seasons in two sites located in the CIA, show that GPR allows an accurate reconstruction of the snow-soil interface and the thickness of the snow cover, while VNA measurements, performed by inserting the probes horizontally inside a trench dug in the snow, allows to estimate the snow density and water content: the comparison with gravimetric measurements shows a good agreement within the uncertainties, especially in the case of wet snow. In conclusion, this work has shown that combining GPR and FDR technique represents a promising tool to characterize snowpacks and their stratigraphy, allowing a continuous monitoring fundamental for the validation of satellite measurements.

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