G. Salme

Sapienza University of Rome, Roma, Latium, Italy

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Publications (125)181.41 Total impact

  • Giovanni Salmè
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    ABSTRACT: A short review of a novel approach, based on the Nakanishi perturbation-theory integral representation and devised for solving the Bethe-Salpeter equation directly in Minkowski space, is presented. The two ingredients for constructing such a new tool are: i) the Nakanishi perturbation-theory integral representations of the V-leg transition amplitudes and ii) the Light- front framework, that also allows one to gain insights into the Fock content of the states of an interacting system. Numerical results, corresponding to the Bethe-Salpeter equation in ladder approximation, for a simple system, composed by two massive scalars interacting through the exchange of a massive scalar, are provided for illustrating the effectiveness of the approach.
    Journal of Physics Conference Series 07/2014; 527(1):012026.
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    ABSTRACT: A preliminary analysis of polarization-transfer data at large scattering angle (70°), obtained in an experiment of real Compton scattering on proton, performed in Hall-C of Jefferson Lab, is presented. It is also discussed the relevance of this kind of experiments for shedding light on the non-perturbative structure of the proton, at low energy, and on the transition from the non-perturbative regime to the perturbative one, that occurs at high energy. Moreover, the possibility to extract Compton form factors and the Generalized Parton Distributions, one of the most promising theoretical tool to determine the total angular momentum contribution of quarks and gluons to nucleon spin, is emphasized.
    02/2014;
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    ABSTRACT: The Bethe-Salpeter Equation for a two-scalar, S-wave bound system, interacting through a massive scalar, is investigated within the ladder approximation. By assuming a Nakanishi integral representation of the Bethe-Salpeter amplitude, one can deduce new integral equations that can be solved and quantitatively studied, overcoming the analytic difficulties of the Minkowski space. Finally, it is shown that the Light-front distributions of the valence state, directly obtained from the Bethe-Salpeter amplitude, open an effective window for studying the two-body dynamics.
    02/2014;
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    ABSTRACT: The possibility of improving the description of the semi-inclusive deep inelastic electron scattering off polarized 3He, that provides information on the neutron single spin asymmetries, is illustrated. In particular, the analysis at finite momentum transfers in a Poincare' covariant framework is outlined and a generalized eikonal approach to include final state interaction is presented.
    Few-Body Systems 02/2014; · 1.05 Impact Factor
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    ABSTRACT: The Bethe-Salpeter Equation for a bound system, composed by two massive scalars exchanging a massive scalar, is quantitatively investigated in ladder approximation, within the Nakanishi integral representation approach. For the S-wave case, numerical solutions with a form inspired by the Nakanishi integral representation, have been calculated. The needed Nakanishi weight functions have been evaluated by solving two different eigenequations, obtained directly from the Bethe-Salpeter equation applying the Light-Front projection technique. A remarkable agreement, in particular for the eigenvalues, has been achieved, numerically confirming that the Nakanishi uniqueness theorem for the weight functions, demonstrated in the context of the perturbative analysis of the multi-leg transition amplitudes and playing a basic role in suggesting one of the two adopted eigenequations, can be extended to a non perturbative realm. The detailed, quantitative studies are completed by presenting both probabilities and Light-Front momentum distributions for the valence component of the bound state.
    12/2013; 89(1).
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    ABSTRACT: The distorted spin-dependent spectral function of a nucleon inside an A=3 nucleus is introduced as a novel tool for investigating the polarized electron scattering off polarized $^3$He in semi-inclusive DIS regime (SiDIS), going beyond the standard plane wave impulse approximation. This distribution function is applied to the study of the spectator SiDIS, $\vec{^3{\rm He}}(\vec e, e' ~{^2}{\rm H})X$, in order to properly take into account the final state interaction between the hadronizing quark and the detected deuteron, with the final goal of a more reliable extraction of the polarized parton-distribution $g_1(x)$ inside a bound proton. Our analysis allows to single out two well-defined kinematical regions where the experimental asymmetries could yield very interesting information: the region where the final state effects can be minimized, and therefore the direct access to the parton distributions in the proton is feasible, and the one where the final state interaction dominates, and the spectator SiDIS reactions can elucidate the mechanism of the quark hadronization itself. The perspectives of extending our approach i) to the mirror nucleus, $^3$H, for achieving a less model-dependent flavor decomposition, and ii) to the asymmetries measured in the standard SiDIS reactions, $\vec e + \vec{^3 {\rm He}} \to e' + h+X$ with $h$ a detected fast hadron, with the aim of extracting the neutron transversity, are discussed.
    07/2013;
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    ABSTRACT: Through an impulse approximation analysis of single spin Sivers and Collins asymmetries in the Bjorken limit, the possibility to extract the quark transverse-momentum distributions in the neutron from semi-inclusive deep inelastic electron scattering off polarized 3He is illustrated. The analysis is generalized to finite momentum transfers in a light-front Poincare' covariant framework, defining the light-front spin-dependent spectral function of a J=1/2 system. The definition of the light-front spin-dependent spectral function for constituent quarks in the nucleon allows us to show that, within the light-front dynamics, only three of the six leading twist T-even transverse-momentum distributions are independent.
    02/2013;
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    ABSTRACT: The possibility to extract the quark transverse-momentum distributions in the neutron from semi-inclusive deep inelastic electron scattering off polarized 3He is illustrated through an impulse approximation analysis in the Bjorken limit. The generalization of the analysis at finite momentum transfers in a Poincare' covariant framework is outlined. The definition of the light-front spin-dependent spectral function of a J=1/2 system allows us to show that within the light-front dynamics only three of the six leading twist T-even transverse-momentum distributions are independent.
    Few-Body Systems 01/2013; 54(7-10). · 1.05 Impact Factor
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    Achim Denig, Giovanni Salme
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    ABSTRACT: The electromagnetic form factors of the proton and the neutron in the timelike region are reviewed. In view of the forthcoming experimental projects devoted to investigate these observables, we present the current status of the field and we emphasize the relevant role, that accurate measurements, refined phenomenological analyses, as well as microscopic models will play with the goal of achieving deeper insights into the structure of the nucleon and its inner dynamics.
    Progress in Particle and Nuclear Physics 10/2012; 68. · 2.26 Impact Factor
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    ABSTRACT: An overview of the vector and tensor Generalized Parton Distributions for a charged pion is presented. Such observables, belonging to the set of quantities fundamental for a detailed investigation of the hadronic inner dynamics, have been evaluated within a fully covariant Constituent Quark Model, based on a proper Ansatz of the pion Bethe-Salpeter Amplitude and the Mandelstam formula for matrix elements of operators acting on relativistic composite systems. Given the very encouraging results already obtained for the vector distribution of a charged pion, the model has been extended to the tensor one, and some preliminary calculations will be illustrated.
    Few-Body Systems 08/2012; 54(5-6). · 1.05 Impact Factor
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    Tobias Frederico, Giovanni Salmè, Michele Viviani
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    ABSTRACT: The Nakanishi perturbative integral representation of the four-dimensional T-matrix is investigated in order to get a workable treatment for scattering states, solutions of the inhomogeneous Bethe-Salpeter Equation, in Minkowski space. The projection onto the null-plane of the four-dimensional inhomogeneous Bethe-Salpeter Equation plays a key role for devising an equation for the Nakanishi weight function (a real function), as in the homogeneous case that corresponds to bound states and it has been already studied within different frameworks. In this paper, the whole formal development is illustrated in detail and applied to a system, composed by two massive scalars interacting through the exchange of a massive scalar. The explicit expression of the scattering integral equations are also obtained in ladder approximation, and, as simple applications of our formalism, some limiting cases, like the zero-energy limit and the Wick-Cutkosky model in the continuum, are presented.
    Physical review D: Particles and fields 12/2011; 85(3).
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    Emanuele Pace, Giovanni Romanelli, Giovanni Salmè
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    ABSTRACT: The pion tensor generalized parton distributions are evaluated within a covariant, analytic constituent quark model. The generalized form factors for the first two Mellin moments and the probability densities of polarized quarks in the impact parameter space are derived and compared with lattice QCD and quark model results.
    Few-Body Systems 12/2011; 52(3-4). · 1.05 Impact Factor
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    ABSTRACT: A realistic study of the SiDIS process 3He(e,e'\pi)X in the Bjorken limit is briefly reviewed, showing that the nuclear effects, present in the extraction of the neutron information, are largely under theoretical control, within an Impulse-Approximation approach. In view of the forthcoming experimental data, we shortly present a novel Poincare' covariant description of the nuclear target, implementing a Light-Front analysis at finite Q^2, within the Bakamijan-Thomas construction of the Poincare' generators. Furthermore, as a by-product of the introduction of a Light-Front spin-dependent spectral function for a J=1/2 system, we straightforwardly extend our analysis to the quark-quark correlator, obtaining three new exact relations between the six leading-twist Transverse-Momentum Dependent distributions.
    10/2011;
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    ABSTRACT: Within the Light-Front Hamiltonian Dynamics, we are extending our investigation of the deuteron electromagnetic properties by adding new, dynamical two-body terms to the one-body current operator, introduced in previous works. These two-body contributions are generated in a four-dimensional Yukawa model (two fermions interacting through a pion) from an analysis of the Light-Front-projected current that acts on the three-dimensional valence component and fulfills the Ward-Takahashi identity. Preliminary results for the magnetic moment and the non valence probability are shown.
    10/2011;
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    ABSTRACT: The relativistic distorted-wave impulse approximation is used to describe the 3He(e, e′ p)2H process. We describe the 3He nucleus within the adiabatic hyperspherical expansion method with realistic nucleon-nucleon interactions. The overlap between the 3He and the deuteron wave functions can be accurately computed from a three-body calculation. The nucleons are described by solutions of the Dirac equation with scalar and vector (S–V) potentials. The wave function of the outgoing proton is obtained by solving the Dirac equation with a S–V optical potential fitted to elastic proton scattering data on the residual nucleus. Within this theoretical framework, we compute the cross section of the reaction and other observables like the transverse-longitudinal asymmetry, and compare them with the available experimental data measured at JLab.
    Few-Body Systems 01/2011; 50(1):359-362. · 1.05 Impact Factor
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    ABSTRACT: The electromagnetic properties of the deuteron are investigated within a Light-Front Hamiltonian Dynamics framework, with a current operator that contains both one-body and two-body contributions. In this work, we are considering new two-body contributions, with a dynamical nature generated within a Yukawa model and a structure inspired by a recent analysis of the current operator, that acts on the three-dimensional valence component and fulfills the Ward-Takahashi identity. Preliminary results for the magnetic moment are shown.
    11/2010;
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    ABSTRACT: A recent approach for constructing an exact 3D reduction of the 4D matrix elements of the electromagnetic current for an interacting two-fermion system, is briefly reviewed. The properties of the obtained 3D current, like the fulfillment of the Ward-Takashi Identity and its Fock decomposition, will be illustrated in relation with future applications to few-nucleon systems. Comment: 8 pages, 1 Fig. Suitable. cls added. Proceedings of 12th Conference on 'Theoretical Nuclear Physics in Italy', Cortona, October 2008
    Journal of Physics Conference Series 02/2010;
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    ABSTRACT: A simple, but fully-covariant model for describing neutral Vector Mesons, in both light and heavy sectors, is briefly illustrated. The main ingredients of our relativistic constituent model are i) an Ansatz for the Bethe-Salpeter vertex for Vector Mesons, and ii) a Mandelstam-like formula for the electromagnetic decay widths. The free parameters of our approach are fixed through a comparison with the valence transverse-momentum distribution, $n(k_\perp)$, obtained within phenomenological Light-Front Hamiltonian Dynamics models reproducing the mass spectra. Preliminary results for the transverse-momentum distributions, the parton distribution and the electromagnetic decay constants are shown. Comment: 6 pages, 4 figures. Proceedings of LC2009, to appear in Nucl. Phys. B suppl
    Nuclear Physics B - Proceedings Supplements 02/2010; · 0.88 Impact Factor
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    ABSTRACT: Longitudinal and transverse parton distributions for pion and nucleon are calculated from hadron vertexes obtained by a study of form factors within relativistic quark models. The relevance of the one-gluon-exchange dominance at short range for the behavior of the form factors at large momentum transfer and of the parton distributions at the end points is stressed.
    AIP Conference Proceedings. 02/2010; 1257(1).
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    ABSTRACT: Longitudinal and transverse quark momentum distributions in the nucleon are calculated from a phenomenological quark-nucleon vertex function obtained through an investigation of the nucleon electromagnetic form factors within a light-front framework. Comment: 6 pages, 11 figs. proceedings of LC2009, to appear in Nucl. Phys. B
    02/2010;

Publication Stats

1k Citations
181.41 Total Impact Points

Institutions

  • 1984–2014
    • Sapienza University of Rome
      • Department of Physics
      Roma, Latium, Italy
  • 1980–2013
    • INFN - Istituto Nazionale di Fisica Nucleare
      Frascati, Latium, Italy
  • 1980–2008
    • University of Rome Tor Vergata
      • Dipartimento di Fisica
      Roma, Latium, Italy
  • 2003
    • Osaka University
      Suika, Ōsaka, Japan
  • 1989
    • Istituto Superiore di Sanità
      Roma, Latium, Italy
  • 1983–1989
    • Università degli Studi di Perugia
      • Department of Physics
      Terni, Umbria, Italy
  • 1982
    • Università degli Studi Europea di Roma
      Roma, Latium, Italy