Direct numerical computation of disorder parameters

In the framework of various statistical models as well as of mechanisms for color confinement, disorder parameters can be developed which are generally expressed as ratios of partition functions and whose numerical determination is usually challenging. We develop an efficient method for their computation and apply it to the study of dual superconductivity in 4d compact U(1) gauge theory.Comment: 5 pages, 6 figures. Final revised version published in PR

Covariant EBK quantization of the electromagnetic two-body problem

We discuss a method to transform the covariant Fokker action into an implicit two-degree-of-freedom Hamiltonian for the electromagnetic two-body problem with arbitrary masses. This dynamical system appeared 100 years ago and it was popularized in the 1940's by the still incomplete Wheeler and Feynman program to quantize it as a means to overcome the divergencies of perturbative QED. Our finite-dimensional implicit Hamiltonian is closed and involves no series expansions. The Hamiltonian formalism is then used to motivate an EBK quantization based on the classical trajectories with a non-perturbative formula that predicts energies free of infinities.Comment: 21 page

Improved analysis of the bounds from the electroweak precision tests on the 4-site model

We present a new complete analysis of the electroweak precision observables within the recently proposed 4-site Higgsless model, which is based on the SU(2)_L x SU(2)_1 x SU(2)_2 x U(1)_Y gauge symmetry and predicts six extra gauge bosons, W_{1,2} and Z_{1,2}. Within the epsilon_i (i=1,2,3,b) parametrization, we compute for the first time the EWPT bounds via a complete numerical algorithm going beyond commonly used approximations. Both epsilon_{1,3} impose strong constraints. Hence, it is mandatory to consider them jointly when extracting EWPT bounds and to fully take in to account the correlations among the electroweak precison measurements. The phenomenological consequence is that the extra gauge bosons must be heavier than 250 GeV. Their couplings to SM fermions, even if bounded, might be of the same order of magnitude than the SM ones. In contrast to other Higgsless models, the 4-site model is not fermiophobic. The new gauge bosons could thus be discovered in the favoured Drell-Yan channel already during the present run of the LHC experiment.Comment: Latex file, 35 pages, 10 figures, corrected typos, published versio

Grammatizzazioni dello spazio-corpo: tra algoritmizzazione ed eccedenze

Lo spazio definito dalle nuove tecnologie digitali viene sempre più frequentemente descritto attorno ai concetti problematici di condivisione, cooperazione, moltiplicazione dei punti di enunciazione, facilitazione e accesso (più) democratico ai beni e ai servizi. Più realisticamente può essere raccontato come uno spazio fondato sulla chimera della neutralità e della calcolabilità dell'esistente. A partire dal tentativo continuo (e mai compiuto) di gestione delle pluri-potenzialità dello spazio-corpo attraverso la grammatizzazione algoritmica, ci interessa indagare la cartografia degli anfratti, delle zone di accumulo dell'ingestibile, coestensivi o conflittuali alla spazialità definita dal digitale. Fuggiamo tuttavia l'idea che le stesse spazialità definite dall'umano, dalla macchina, dal digitale, siano segmentate e definite autonomamente e senza ibridazioni. Partiamo piuttosto dal presupposto per il quale lo spazio-corpo è di per sé macchinico in quanto spazio dove è possibile esternalizzarele funzioni del capitale fisso (Marazzi, 2005); uno spazio che accoglie quelli che, nel linguaggio marxiano, si definiscono mezzi di produzione e che includono conoscenze acquisite, grammatiche produttive ed esperienze di lavoro passate. Questa porosità si traduce in uno spazio dove la macchina digitale e il vivente appaiono co-innervati in un intreccio macchinico vivo che coinvolge corpi, relazioni sociali, infrastrutture di comunicazione e network digitali. Se da una parte non è difficile immaginare la permeabilità di questo spazio macchinico vivente alla grammatizzazione inscritta nei codici algoritmici che stanno alla base delle nuove tecnologie digitali (Pasquinelli, 2014) dall’altra è necessario individuare quelle aree di impermeabilità, di frizione e di resistenza alla calcolabilità/automazione che mostrano come lo spazio-corpo possa riconfigurarsi in quanto terreno di lotta e di sperimentazione di pratiche liberanti e forme di autonomia o più drammaticamente di effetti drammatici indesiderati. E' il caso della necropolotica (Romagnoli 2012), quella particolare modalità di esercizio del biopotere che descrive il processo di avvelenamento del corpo che mangia i frutti e respira i fumi di un ciclo produttivo che ha ipotecato la stessa biosfera per l'accumulazione forsennata di profitto. Oppure è il caso della sessualità, che per quanto soggetta a sottilissime forme di biocontrollo ne eccede continuamente i perimetri per sondare spazialità sempre nuove ed irriducibili. O ancora, si pensi alle spazialità ibride che si producono attraverso le pratiche politiche collettive, spazialità per le quali l'ibridazione macchinica viene sottoposta simultaneamente a processi di cattura e di liberazione assolutamente non controllabili dalle grammatizzazioni algoritmiche

Quantum spin Hall effect in bound states in continuum

Moving the polarization of the incident wave along a meridian of the Poincaré sphere, experimentally we show that the coupling with the fundamental Bloch's surface waves of the mode, provide a spatially coherent, macroscopic spinmomentum locked propagation along the symmetry axes of the PhCM. This novel mechanism of light-spin manipulation enables a versatile implementation of spin-optical structures that may pave the way to novel strategies for light spin technology and photonic multiplatform implementations

Assessment of poststress left ventricular ejection fraction by gated SPECT: comparison with equilibrium radionuclide angiocardiography

PURPOSE: We compared left ventricular (LV) ejection fraction obtained by gated SPECT with that obtained by equilibrium radionuclide angiocardiography in a large cohort of patients. METHODS: Within 1 week, 514 subjects with suspected or known coronary artery disease underwent same-day stress-rest (99m)Tc-sestamibi gated SPECT and radionuclide angiocardiography. For both studies, data were acquired 30 min after completion of exercise and after 3 h rest. RESULTS: In the overall study population, a good correlation between ejection fraction measured by gated SPECT and by radionuclide angiocardiography was observed at rest (r=0.82, p<0.0001) and after stress (r=0.83, p<0.0001). In Bland-Altman analysis, the mean differences in ejection fraction (radionuclide angiocardiography minus gated SPECT) were -0.6% at rest and 1.7% after stress. In subjects with normal perfusion (n=362), a good correlation between ejection fraction measured by gated SPECT and by radionuclide angiocardiography was observed at rest (r=0.72, p<0.0001) and after stress (r=0.70, p<0.0001) and the mean differences in ejection fraction were -0.9% at rest and 1.4% after stress. Also in patients with abnormal perfusion (n=152), a good correlation between the two techniques was observed both at rest (r=0.89, p<0.0001) and after stress (r=0.90, p<0.0001) and the mean differences in ejection fraction were 0.1% at rest and 2.5% after stress. CONCLUSION: In a large study population, a good agreement was observed in the evaluation of LV ejection fraction between gated SPECT and radionuclide angiocardiography. However, in patients with perfusion abnormalities, a slight underestimation in poststress LV ejection fraction was observed using gated SPECT as compared to equilibrium radionuclide angiocardiography

Minimizers with discontinuous velocities for the electromagnetic variational method

The electromagnetic two-body problem has \emph{neutral differential delay} equations of motion that, for generic boundary data, can have solutions with \emph{discontinuous} derivatives. If one wants to use these neutral differential delay equations with \emph{arbitrary} boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous derivatives are also expected, as we show here. The variational method defines continuous trajectories with piecewise defined velocities and accelerations, and electromagnetic fields defined \emph{by} the Euler-Lagrange equations \emph{% on} trajectory points. Here we use the piecewise defined minimizers with the Li{\'{e}}nard-Wierchert formulas to define generalized electromagnetic fields almost everywhere (but on sets of points of zero measure where the advanced/retarded velocities and/or accelerations are discontinuous). Along with this generalization we formulate the \emph{generalized absorber hypothesis} that the far fields vanish asymptotically \emph{almost everywhere%} and show that localized orbits with far fields vanishing almost everywhere \emph{must} have discontinuous velocities on sewing chains of breaking points. We give the general solution for localized orbits with vanishing far fields by solving a (linear) neutral differential delay equation for these far fields. We discuss the physics of orbits with discontinuous derivatives stressing the differences to the variational methods of classical mechanics and the existence of a spinorial four-current associated with the generalized variational electrodynamics.Comment: corrected minor typo: piecewise differentiable on closed instead of open interval

Recent Advances in Fairness Analysis of User Profiling Approaches in E-Commerce with Graph Neural Networks

User profiling is a critical procedure for e-commerce applications that captures online users’ attributes, understands user models, supports the provision of tailor-made goods and services, and improves user satisfaction. With the advent of novel technologies like Graph Neural Networks (GNNs), the performance of user profiling approaches has improved by leaps and bounds, in step with the growing concern about data and algorithmic fairness. This paper provides an overview of recent advances in the fairness analysis of GNN-based models for user profiling in the e-commerce domain. We present the results of our recent works addressing the need for an accurate analysis of state-of-the-art models and the lack of a unified tool for enabling any user to perform a fairness analysis on a specific dataset by leveraging the most performing models in this context. Our goal is to foster discussions on the potential implications of our work within the community, not only from a technical view but also from domain experts’ perspective