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Probing Gravitational-Wave Extra Polarizations with Ground-Based Interferometers
Get PDFGravitational waves (GWs) were first predicted by Albert Einstein in his theory of General Relativity (GR) back in 1916 and were directly observed in 2016 by the Ligo-Virgo collaboration for the first time, opening up new horizons to make us better understand our Universe. Moreover, interplays among upcoming detectors are expected to resolve GW sources with incredible precision and the Stochastic Gravitational Wave Background (of astrophysical and/or of cosmological origin) is expected to be detected in the future, making the following decades an exciting period for the study of GWs. When general metric theories of gravity are considered, at most 6 gravitational wave polarization modes are allowed: 2 tensor modes, already predicted by General Relativity, 2 scalar modes and 2 vector modes. Therefore the importance of testing for the presence of such extra-polarization modes is clear: if they are detected new physics is discovered and GR needs to be extended. In this thesis we consider a cosmological stochastic background of gravitational waves (SGWB) involving a mixture of all possible modes and we discuss their detectability and separation by cross-correlating -generation interferometers on Earth, such as Kagra, Ligo, Virgo with their planned upgrades ``Advanced Ligo” and ``Advanced Virgo” and upcoming -generation ground-based detectors, such as Einstein Telescope (ET) and Cosmic Explorer (CE). The key quantity we look for is the gravitational wave background energy density for each polarization mode. In order to distinguish tensor, vector and scalar contributions to the SGWB energy density at least three detectors are needed. Since no ultimate location for ET and CE has been officially decided yet, we investigate different network configurations to show which may be the optimal ones. We find that the Einstein Telescope alone in the proposed triangular configuration cannot separate tensor, vector and scalar contributions to the SGWB exploiting its three detectors. We find that using ET and CE greatly improves sensitivity to extra polarizations and that all networks show almost the same sensitivity to tensor, vector and scalar modes, thus returning similar values for each polarization SGWB energy density contribution. While considering GW frequencies lower than a characteristic value depending on the detector geometry, ground-based interferometers show degenerate responses to the two allowed scalar modes, which then result undistinguishable. We show a possible way to break this degeneracy with -generation interferometers, which are expected to be more sensitive to GWs of higher frequencies. Finally, we consider Earth rotation to investigate and obtain maps of the response of the detectors to different polarizations
Demography of binary neutron stars: the impact of natal kicks and electron-capture supernovae.
Get PDFThis thesis presents a theoretical study on the statistical properties
of binary neutron stars, by means of synthetic stellar populations
simulated with the SEVN code. The work focuses on the impact that
electron-capture supernovae and momentum-conserving natal kicks have on the properties of these binary systems
Evoluzione di sistemi binari per emissione di onde gravitazionali.
Get PDFLe onde gravitazionali, la cui prima osservazione diretta risale al 2015, sono una delle predizioni più importanti della Relatività Generale. In questo lavoro di tesi ho approfondito le basi della teoria della Relatività Generale e le principali relazioni matematiche
per l'emissione di onde gravitazionali da parte di un sistema binario. Ho inoltre sviluppato un codice che permette di integrare l'evoluzione orbitale di un sistema binario per emissione di onde gravitazionali
Il problema del commesso viaggiatore: formulazioni e un'applicazione archeologica
No full textTema centrale della trattazione è il Problema del Commesso Viaggiatore
(dall'inglese "Travelling Salesman Problem", TSP), la cui importanza è
fondamentale in ambiti come la Teoria dei Grafi e la Ricerca Operativa, e che ha destato da subito il mio interesse grazie alle sue straordinarie
applicazioni in campi apparentemente lontani dalla matematica, quali per esempio l'archeologia. La tesi consta di 4 capitoli. Il primo affronta la Programmazione Lineare Intera, e alcuni suoi metodi risolutivi: il Problema del Commesso Viaggiatore infatti può essere formulato come un Programma Lineare Intero. Nel secondo capitolo viene esposto il TSP ponendo particolare attenzione alle sue diverse formulazioni, confrontandone il numero di vincoli. Nel terzo capitolo viene esposta un'applicazione archeologica del TSP legata al problema di seriazione di reperti archeologici, ossia al dover disporre in ordine cronologico tali reperti. Nel quarto capitolo infine ho analizzato diversi siti archeologici
attraverso le tecniche esposte nel capitolo precedente, confrontandone i
risultati. Tali modelli sono stati implementati su AMPL, un linguaggio di
programmazione dedicato a risolvere problemi di ottimizzazion
Il teorema di categoricità di Morley
No full textLa tesi ha come principale obiettivo quello di enunciare e dimostrare il
Teorema di Categoricità di Morle
Spin glass theory with applications to neural networks
No full textIn this thesis we go through three classical models in complex system theory: Ising model, spin glasses model and Hopfield model
Processi Markoviani e convergenza di algoritmi evolutivi
No full textLo scopo di questa tesi è discutere delle condizioni sufficienti affinchè un algoritmo evolutivo converga ad una soluzione ottimale
Adaptive learning in low-power wide-area networks
No full textInternet of Things applications are driving the need for better and
advanced solutions to connect and manage sensors communicating into a smarter world. In this thesis we present preliminary results derived from tests on dual-band Low Power Wide Area Networks, trying to solve both effectiveness and efficiency challenges from a data science point of view.
In the former case, by applying machine learning models with high
performances while keeping the load of sensor networks as low as possible in terms of acknowledgements requested by single nodes, in the latter by storing a simple model in a small device while providing fast and accurate predictions. Statistical inference techniques and online learning algorithms are investigated under non-stationary conditions and adopted for testing multiple practical scenarios, with the aim of estimating the network status in the licensed and unlicensed bands, i.e. NB-IOT and Lorawan respectively
