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Giampaolo Co'

Publications and source records attributed to Giampaolo Co'.

At least 19 recordsLinked to original sources
arXiv2024

Electroweak Evolution Equations and Isospin Conservation

In processes taking place at energies much higher than the weak scale, electroweak corrections can be taken into account by using electroweak evolution equations, that are analogous to the DGLAP equations in QCD. We show that weak isospin conservation in these equations imposes to modify the expressions of the splitting functions commonly used in the literature. These modifications have a profound impact on the parton distribution functions.

hep-ph↗
arXiv2024

Cross section for supernova axion observation in neutrino water Cherenkov detectors

Axions coupled to nucleons might be copiously emitted from core-collapse supernovae (SNe). If the axion-nucleon coupling is strong enough, axions would be emitted from the SN as a burst and, reaching Earth, may excite the oxygen nuclei in water Cherenkov detectors (${}^{16}{\rm O} + a \to {}^{16}{\rm O}^{*}$). This process will be followed by decay(s) of the excited state resulting in an emission of photons and thus providing a possibility for a direct detection of axions from a Galactic SN in large underground neutrino Cherenkov detectors. Motivated by this possibility, we present an updated calculation of axion-oxygen cross section obtained by using self-consistent continuum Random Phase Approximation. We calculate the branching ratio of the oxygen nucleus de-excitation into gamma-rays, neutrons, protons and $α$-particles and also consider photon emission from secondary nuclei to compute a total $γ$ spectrum created when axions excite ${}^{16}{\rm O}$. These results are used to revisit the detectability of axions from SN 1987A in Kamiokande-II.

hep-ph↗
arXiv2024

Getting the most on supernova axions

Axion-like particles (ALPs) coupled to nucleons might be copiously emitted from a supernova (SN) core. We extend existing bounds on free-streaming ALPs to the case in which these are so strongly-interacting with the nuclear matter to be trapped in the SN core. For strongly-interacting ALPs, we also extend the bound from the absence of an ALP-induced signal in Kamiokande-II neutrino detector at the time of SN 1987A. We find that combining the different arguments, SNe exclude values of ALP-nucleon coupling $g_{aN}\gtrsim10^{-9}$ for ALP masses $m_a\lesssim 1\,\mathrm{MeV}$. Remarkably, in the case of canonical QCD axion models, the SN bounds exclude all values of $m_a \gtrsim 10^{-2}\,\mathrm{eV}$. This result prevents the possibility for current and future cosmological surveys to detect any signatures due to hot dark matter QCD axion mass.

hep-ph↗
arXiv2023

Introducing the Random Phase Approximation Theory

Random Phase Approximation (RPA) is the theory most commonly used to describe the excitations of many-body systems. In this article, the secular equations of the theory are obtained by using three different approaches: the equation of motion method, the Green's function perturbation theory and the time-dependent Hartree--Fock theory. Each approach emphasizes specific aspects of the theory overlooked by the other methods. Extensions of the RPA secular equations to treat the continuum part of the excitation spectrum and also the pairing between the particles composing the system are presented. Theoretical approaches which overcome the intrinsic approximations of RPA are outlined.

nucl-th↗
arXiv2018

Axion emission and detection from a Galactic supernova

A Galactic supernova (SN) axion signal would be detected in a future neutrino Mton-class water Cherenkov detector, such as the proposed Hyper-Kamiokande in Japan. The main detection channel for axions is absorption on the oxygen nuclei in the water. The subsequent oxygen de-excitation leads to a potentially detectable gamma signal. In this contribution we present a calculation of the SN axion signal and discuss its detectability in Hyper-Kamiokande.

hep-ph↗
arXiv2018

Analytical and numerical analysis of the complete Lipkin-Meshkov-Glick Hamiltonian

The Lipkin-Meshkov-Glick is a simple, but not trivial, model of a quantum many-body system which allows us to solve the many-body Schrödinger equation without making any approximation. The model, which in its unperturbed case is composed only by two energy levels, includes two interacting terms. A first one, the $V$ interaction, which promotes or degrade pairs of particles, and a second one, the $W$ interaction, which scatters one particle in the upper and another in the lower energy level. In comparing this model with other approximation methods, the $W$ term interaction is often set to zero. In this paper, we show how the presence of this interaction changes the global structure of the system, generates degeneracies between the various eigenstates and modifies the energy eigenvalues structure. We present analytical solutions for systems of two and three particles and, for some specific cases, also for four, six and eight particles. The solutions for systems with more than eight particles are only numerical but their behaviour can be well understood by considering the extrapolations of the analytical results. Of particular interest it is the study of how the $W$ interaction affects the energy gap between the ground state and the first-excited state.

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arXiv2016

Hartree-Fock and Random Phase Approximation theories in a many-fermion solvable model

We present an ideal system of interacting fermions where the solutions of the many-body Schroedinger equation can be obtained without making approximations. These exact solutions are used to test the validity of two many-body effective approaches, the Hartree-Fock and the Random Phase Approximation theories. The description of the ground state done by the effective theories improves with increasing number of particles.

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arXiv2012

Tensor and tensor-isospin terms in the effective Gogny interaction

We discuss the need of including tensor terms in the effective Gogny interaction used in mean-field calculations. We show in one illustrative case that, with the usual tensor term that is employed in the Skyrme interaction (and that allows us to separate the like-nucleon and the neutron-proton tensor contributions), we can describe the evolution of the N=28 neutron gap in calcium isotopes. We propose to include a tensor and a tensor-isospin term in finite-range interactions of Gogny type. The parameters of the two tensor terms allow us to treat separately the like-nucleon and the neutron-proton contributions. Two parameterizations of the tensor terms have been chosen to reproduce different neutron single-particle properties in the 48Ca nucleus and the energy of the first 0- state in the 16O nucleus. By employing these two parameterizations we analyze the evolution of the N=14, 28, and 90 neutron energy gaps in oxygen, calcium and tin isotopes, respectively. We show that the combination of the parameters governing the like-nucleon contribution is crucial to correctly reproduce the experimental (where available) or shell-model trends for the evolution of the three neutron gaps under study.

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arXiv2006

Random Phase Approximation and neutrino-nucleus cross sections

The Random Phase Approximation theory is used to calculate the total cross sections of electron neutrinos on $^{12}$C nucleus. The role of the excitation of the discrete spectrum is discussed. A comparison with electron scattering and muon capture data is presented. The cross section of electron neutrinos coming from muon decay at rest is calculated.

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arXiv2006

Nuclear models and neutrino cross sections

Merits and faults of the effective theory Random Phase Approximations are discussed in the perspective of its use in the prediction of neutrino-nucleus cross sections.

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arXiv2005

Excitation of nuclear giant resonances in neutrino scattering off nuclei

The cross sections for neutrino scattering off the 12C and 16O nuclei are calculated within the framework of the continuum Random Phase Approximation. A model to consider also the final state interactions is developed. Total charge-conserving and charge-exchange cross sections for both electron neutrinos and antineutrinos have been calculated up to projectile energies of 100 MeV. The sensitivity of the cross sections to the residual interaction and to the final state interactions is investigated. A direct comparison between neutrino and electron scattering cross sections calculated under the same kinematic conditions is presented. We found remarkable differences between electromagnetic and weak nuclear responses. The model is applied to describe cross sections of neutrinos produced by muon decay at rest and in supernovae explosions.

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arXiv2004

Nuclear Physics with electroweak probes

The last few years activity of the Italian community concerning nuclear physics with electroweak probes is reviewed.Inclusive quasi-elastic electron-scattering, photon end electron induced one- and two-nucleon emission are considered. The scattering of neutrinos off nuclei in the quasi-elastic region is also discussed.

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arXiv2004

Photo-emission of two protons from nuclei

The photo-emission of two protons from the $^{12}$C, $^{16}$O and $^{40}$Ca nuclei is investigated. Aim of the work is the study of the possibilities offered by this probe to obtain information about the characteristics of the short-range correlations. We have also evaluated the effects of the two-body $Δ$-currents which, in this processes, compete with those produced by the short-range correlations. Our results show that ($γ$,pp) processes could be more useful than (e,e'pp) for the study of the short-range correlations.

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arXiv2004

Short-range nucleon-nucleon correlation effects in photon- and electron-nucleus reactions

The role played by nucleon-nucleon short-range correlations in photon- and electron-nucleus reactions is analyzed with a model which includes all the diagrams containing a single correlation function. The excitation of low-lying high-spin states, the reactions (e,e'), (e,e'N) and ($γ$,N) and the two-proton emission by both electrons and real photons are investigated. The results obtained for doubly-closed shell nuclei show that ($γ$,pp) appears to be the most adequate process to identify short-range correlations in the clearer way.

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arXiv2003

Two Proton Emission with Electromagnetic Probes

A model to study two-proton emission from nuclei induced by electromagnetic probes is developed. The process is due to one-body electromagnetic operators, acting together with short-range correlations, and two-body $Δ$ currents. The model includes all the diagrams containing a single correlation function. The sensitivity of the cross section to the details of the correlation function is studied by using realistic and schematic correlations. Results for the $^{16}$O nucleus are presented.

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arXiv2002

Two-proton emission induced by electron scattering

We present a model to describe the emission of two protons in electron scattering experiments. The process is induced by one-body electromagnetic operators acting together with short-range correlations, and by two-body Delta currents. The model includes all the diagrams containing a single correlation function. The sensitivity of the cross section to the details of the correlation function is studied by using realistic and schematic correlations. Results for the 16O nucleus are presented.

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arXiv2002

Short-range correlations in finite nuclear systems

Recent results concerning the use of the Correlated Basis Function to investigate the ground state properties of medium-heavy doubly magic nuclei with microscopic interactions are presented. The calculations have been done by considering a Short-Range Correlation between nucleons. The possibility of identifying effects produced by Short-Range Correlations in electromagnetically induced phenomena is discussed.

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