60 research outputs found

    Introduzione al modello a bosoni interagenti

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    Nel 1974 Akito Arima e Francesco Iachello formularono un nuovo modello nucleare con l'obiettivo di descrivere le proprietà collettive dei nuclei pari-pari, attraverso una reinterpretazione dell'interazione tra i nucleoni di valenza, configurate come interazioni di tipo bosonico. Il modello, detto Modello a Bosoni Interagenti (e abbreviato con IBM), prevedeva come idea fondamentale quella che i fermioni nucleari si potessero accoppiare in oggetti con spin intero, di fatto bosoni. L'obiettivo della trattazione è duplice. In primo luogo consta nell'analizzare la teoria alla base del modello, sfruttando gli strumenti matematici delle algebre di Lie e del formalismo della seconda quantizzazione. In secondo luogo consiste nel valutare l'accordo del modello stesso con i dati sperimentali, eseguendo calcoli con il codice IBAR e ricavando tramite quest’ultimo le energie e i numeri quantici dei livelli di parità positiva e le intensità ridotte delle transizioni di quadrupolo elettrico fra i livelli

    Adaptive mesh refinement for global stability analysis of transitional flows

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    In this work, we introduce the novel application of the adaptive mesh refinement (AMR) technique in the global stability analysis of incompressible flows. The design of an accurate mesh for transitional flows is crucial. Indeed, an inadequate resolution might introduce numerical noise that triggers premature transition. With AMR, we enable the design of three different and independent meshes for the non-linear base flow, the linear direct and adjoint solutions. Each of those is designed to reduce the truncation and quadrature errors for its respective solution, which are measured via the spectral error indicator. We provide details about the workflow and the refining procedure. The numerical framework is validated for the two-dimensional flow past a circular cylinder, computing a portion of the spectrum for the linearised direct and adjoint Navier-Stokes operators.Comment: To be submitted ICOSAHOM202

    Linear stability of Poiseuille flow over a steady spanwise Stokes layer

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    The temporal linear stability of plane Poiseuille flow modified by spanwise forcing applied at the walls is considered. The forcing consists of a stationary streamwise distribution of spanwise velocity that generates a steady transversal Stokes layer, known to reduce skin-friction drag in a turbulent flow with little energetic cost. A large numerical study is carried out, where the effects of both the physical and the discretization parameters are thoroughly explored, for three representative subcritical values of the Reynolds number Re. Results show that the spanwise Stokes layer significantly affects the linear stability of the system. For example, at Re=2000 the wall forcing is found to more than double the negative real part of the least-stable eigenvalue, and to decrease by nearly a factor of 4 the maximum transient growth of perturbation energy. These observations are Re dependent and further improve at higher Re. Comments on the physical implications of the obtained results are provided, suggesting that spanwise forcing might be effective to obtain at the same time a delayed transition to turbulence and a reduced turbulent friction

    Linear stability of Poiseuille flow over a steady spanwise Stokes layer

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    The temporal linear stability of plane Poiseuille flow modified by spanwise forcing applied at the walls is considered. The forcing consists of a stationary streamwise distribution of spanwise velocity that generates a steady transversal Stokes layer, known to reduce skin-friction drag in a turbulent flow with little energetic cost. A large numerical study is carried out, where the effects of both the physical and the discretization parameters are thoroughly explored, for three representative subcritical values of the Reynolds number Re. Results show that the spanwise Stokes layer significantly affects the linear stability of the system. For example, at Re=2000 the wall forcing is found to more than double the negative real part of the least-stable eigenvalue, and to decrease by nearly a factor of four the maximum transient growth of perturbation energy. These observations are Re-dependent and further improve at higher ReRe. Comments on the physical implications of the obtained results are provided, suggesting that spanwise forcing might be effective to obtain at the same time a delayed transition to turbulence and a reduced turbulent friction.Comment: Under consideration by PR

    Semi-Visible Dark Photon Phenomenology at the GeV Scale

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    In rich dark sector models, dark photons heavier than tens of MeV can behave as semi-visible particles: their decays contain both visible and invisible final states. We present models containing multiple dark fermions which allow for such decays and inscribe them in the context of inelastic dark matter and heavy neutral leptons scenarios. Our models represent a generalization of the traditional inelastic dark matter model by means of a charge conjugation symmetry. We revisit constraints on dark photons from e+e−e^+e^- colliders and fixed target experiments, including the effect of analysis vetoes on semi-visible decays, A′→ψi(ψj→ψkℓ+ℓ−)A^\prime \to \psi_i (\psi_j \to \psi_k \ell^+\ell^-). We find that in some cases, the BaBar and NA64 experiments no longer exclude large kinetic mixing, ε∼10−2\varepsilon \sim 10^{-2}, and, specifically, the related explanation of the discrepancy in the muon (g−2)(g-2). This reopens an interesting window in parameter space for dark photons with exciting discovery prospects. We point out that a modified missing-energy search at NA64 can target short-lived A′A^\prime decays and directly probe the newly-open parameter space.Comment: 41 pages, 22 figures, version published in PR

    Dark matter in the Higgs resonance region

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    The singlet scalar Higgs portal model provides one of the simplest explanations of dark matter in our Universe. Its Higgs resonant region, mDM≈mh/2m_\text{DM}\approx m_h/2, has gained particular attention, being able to reconcile the tension between the relic density measurement and direct detection constraints. Interestingly, this region is also preferred as an explanation of the Fermi-LAT γ\gamma-ray Galactic center excess. We perform a detailed study of this model using γ\gamma-ray data from the Galactic center and from dwarf spheroidal galaxies and combine them with cosmic-ray antiproton data from the AMS-02 experiment that shows a compatible excess. In the calculation of the relic density, we take into account effects of early kinetic decoupling relevant for resonant annihilation. The model provides excellent fits to the astrophysical data either in the case the dark matter candidate constitutes all or a subdominant fraction of the observed relic density. We show projections for future direct detection and collider experiments to probe these scenarios.Comment: 21 pages, 15 figures. For the SingletScalar_DM package, see https://github.com/dimauromattia/SingletScalar_DM . This version matches the published version in the PRD journa

    A panorama of new-physics explanations to the MiniBooNE excess

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    The MiniBooNE low-energy excess stands as an unexplained anomaly in short-baseline neutrino oscillation experiments. It has been shown that it can be explained in the context of dark sector models. Here, we provide an overview of the possible new-physics solutions based on electron, photon, and dilepton final states. We systematically discuss the various production mechanisms for dark particles in neutrino-nucleus scattering. Our main result is a comprehensive fit to the MiniBooNE energy spectrum in the parameter space of dark neutrino models, where short-lived heavy neutral leptons are produced in neutrino interactions and decay to e+e−e^+e^- pairs inside the detector. For the first time, other experiments will be able to directly confirm or rule out dark neutrino interpretations of the MiniBooNE low-energy excess.Comment: 35 pages, 21 figure

    DarkNews: a Python-based event generator for heavy neutral lepton production in neutrino-nucleus scattering

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    We introduce DarkNews, a lightweight Python-based Monte-Carlo generator for beyond-the-Standard-Model neutrino-nucleus scattering. The generator handles the production and decay of heavy neutral leptons via additional vector or scalar mediators, as well as through transition magnetic moments. DarkNews samples pre-computed neutrino-nucleus upscattering cross sections and heavy neutrino decay rates to produce dilepton and single-photon events in accelerator neutrino experiments. We present two case studies with differential distributions for models that can explain the MiniBooNE excess. The aim of this code is to aid the neutrino theory and experimental communities in performing searches and sensitivity studies for new particles produced in neutrino upscattering.Comment: 18 pages, 6 tables, 8 figure

    Robots Are Not All the Same: Young Adults' Expectations, Attitudes, and Mental Attribution to Two Humanoid Social Robots

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    The human physical resemblance of humanoid social robots (HRSs) has proven to be particularly effective in interactions with humans in different contexts. In particular, two main factors affect the quality of human-robot interaction, the physical appearance and the behaviors performed by the robot. In this study, we examined the psychological effect of two HRSs, NAO and Pepper. Although some studies have shown that these two robots are very similar in terms of the human likeness, other evidence has shown some differences in their design affecting different psychological elements of the human partner. The present study aims to analyze the variability of the attributions of mental states (AMS), expectations of robotic development and negative attitudes as a function of the physical appearance of two HRSs after observing a real interaction with a human (an experimenter). For this purpose, two groups of young adults were recruited, one for the NAO

    Studying dark matter with MadDM 3.1: a short user guide

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    MadDM is an automated numerical tool for the computation of dark-matter observables for generic new physics models. We announce version 3.1 and summarize its features. Notably, the code goes beyond the mere cross-section computation for direct and indirect detection. For instance, it allows the user to compute the fully differential nuclear recoil rates as well as the energy spectra of photons, neutrinos and charged cosmic rays for arbitrary 2→n2\to n annihilation processes. This short user guide equips researchers with all the relevant information required to readily perform comprehensive phenomenological studies of particle dark-matter models.Comment: 17 pages + references; contribution to "Tools for High Energy Physics and Cosmology" (TOOLS2020), 2-6 Nov. 2020, IP2I Lyon, Franc
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