# G. Salme - INFN Rome, Italy

## Contact Details

NameG. Salme |
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AffiliationINFN Rome, Italy |
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CityFrascati |
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CountryItaly |
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## Pubs By Year |
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## External Links |
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## Pub CategoriesHigh Energy Physics - Phenomenology (41) Nuclear Theory (35) High Energy Physics - Experiment (5) Physics - Strongly Correlated Electrons (5) Nuclear Experiment (3) High Energy Physics - Theory (2) Physics - Soft Condensed Matter (1) Physics - Mesoscopic Systems and Quantum Hall Effect (1) |

## Publications Authored By G. Salme

Semi-inclusive deep inelastic electron scattering off polarized 3He is studied in a non-relativistic framework, using a distorted spin-dependent spectral function for 3He to take care of the final state interaction between the observed pion and the remnant. A simple procedure is shown to be valuable for the extraction of Sivers and Collins asymmetries for the neutron fromthe corresponding asymmetries for 3He. To extend this study in a relativistic framework, a novel approach for a Poincar\'e covariant description of nuclear dynamics is presented, based on the light-front Hamiltonian dynamics. Read More

The semi-inclusive deep inelastic electron scattering off transversely polarized $^3$He, i.e. the process, $e + \vec{^3 {\rm He}} \to e' + h+X$, with $h$ a detected fast hadron, is studied beyond the plane wave impulse approximation. Read More

**Affiliations:**

^{1}INFN-Rome,

^{2}ITA-S. Jose' dos Campos,

^{3}ITA-S. Jose' dos Campos,

^{4}INFN-Pisa

The possibility of solving the Bethe-Salpeter Equation in Minkowski space, even for fermionic systems, is becoming actual, through the applications of well-known tools: i) the Nakanishi integral representation of the Bethe-Salpeter amplitude and ii) the light-front projection onto the null-plane. The theoretical background and some preliminary calculations are illustrated, in order to show the potentiality and the wide range of application of the method. Read More

Jefferson Lab (JLab) is starting a wide experimental program aimed at studying the neutron's structure, with a great emphasis on the extraction of the parton transverse-momentum distributions (TMDs). To this end, Semi-inclusive deep-inelastic scattering (SiDIS) experiments on polarized $^3$He will be carried out, providing, together with proton and deuteron data, a sound flavor decomposition of the TMDs. Given the expected high statistical accuracy, it is crucial to disentangle nuclear and partonic degrees of freedom to get an accurate theoretical description of both initial and final states. Read More

Poincare' covariant definitions for the spin-dependent spectral function and for the momentum distributions within the light-front Hamiltonian dynamics are proposed for a three-fermion bound system, starting from the light-front wave function of the system. The adopted approach is based on the Bakamjian-Thomas construction of the Poincare' generators, that allows one to easily import the familiar and wide knowledge on the nuclear interaction into a light-front framework. The proposed formalism can find useful applications in refined nuclear calculations, like the ones needed for evaluating the EMC effect or the semi-inclusive deep inelastic cross sections with polarized nuclear targets, since remarkably the light-front unpolarized momentum distribution by definition fulfills both normalization and momentum sum rules. Read More

Actual solutions of the Bethe-Salpeter equation for a two-fermion bound system are becoming available directly in Minkowski space, by virtue of a novel technique, based on the so-called Nakanishi integral representation of the Bethe-Salpeter amplitude and improved by expressing the relevant momenta through light-front components, i.e. $k^\pm=k^0 \pm k^3$. Read More

The quantitative investigation of the scalar Bethe-Salpeter equation in Minkowski space, within the ladder-approximation framework, is extended to include the excited states. This study has been carried out for an interacting system composed by two massive bosons exchanging a massive scalar, by adopting (i) the Nakanishi integral representation of the Bethe-Salpeter amplitude, and (ii) the formally exact projection onto the null plane. Our analysis, on one hand, confirms the reliability of the method already applied to the ground state and, on the other one, extends the investigation from the valence distribution in momentum space to the corresponding quantity in the impact-parameter space, pointing out some relevant features, like (i) the equivalence between Minkowski and Euclidean transverse-momentum amplitudes, and (ii) the leading exponential fall-off of the valence wave function in the impact-parameter space. Read More

**Affiliations:**

^{1}MIT,

^{2}Tor Vergata - Rome U.,

^{3}Rutherford-Appleton Lab.,

^{4}INFN - Rome,

^{5}Sapienza - Rome U.

**Category:**High Energy Physics - Phenomenology

We extend the investigation of the Generalized Parton Distribution for a charged pion within a fully covariant constituent quark model, in two respects: (i) calculating the tensor distribution and (ii) adding the treatment of the evolution, needed for achieving a meaningful comparison with both the experimental parton distribution and the lattice evaluation of the so-called generalized form factors. Distinct features of our phenomenological covariant quark model are: (i) a 4D Ansatz for the pion Bethe-Salpeter amplitude, to be used in the Mandelstam formula for matrix elements of the relevant current operators, and (ii) only two parameters, namely a quark mass assumed to hold $m_q=~220$ MeV and a free parameter fixed through the value of the pion decay constant. The possibility of increasing the dynamical content of our covariant constituent quark model is briefly discussed in the context of the Nakanishi integral representation of the Bethe-Salpeter amplitude. Read More

A distorted spin-dependent spectral function for 3He is considered for the extraction of the transverse-momentum dependent parton distributions in the neutron from semi-inclusive deep inelastic electron scattering off polarized 3He at finite momentum transfers, where final state interactions are taken into account. The generalization of the analysis to a Poincar\'e covariant framework within the light-front dynamics is outlined. Read More

Two topics are presented. The first one is a novel approach for a Poincare' covariant description of nuclear dynamics based on light-front Hamiltonian dynamics. The key quantity is the light-front spectral function, where both normalization and momentum sum rule can be satisfied at the same time. Read More

**Authors:**C. Fanelli, E. Cisbani, D. J. Hamilton, G. Salme, B. Wojtsekhowski, A. Ahmidouch, J. R. M. Annand, H. Baghdasaryan, J. Beaufait, P. Bosted, E. J. Brash, C. Butuceanu, P. Carter, E. Christy, E. Chudakov, S. Danagoulian, D. Day, P. Degtyarenko, R. Ent, H. Fenker, M. Fowler, E. Frlez, D. Gaskell, R. Gilman, T. Horn, G. M. Huber, C. W. de Jager, E. Jensen, M. K. Jones, A. Kelleher, C. Keppel, M. Khandaker, M. Kohl, G. Kumbartzki, S. Lassiter, Y. Li, R. Lindgren, H. Lovelace, W. Luo, D. Mack, V. Mamyan, D. J. Margaziotis, P. Markowitz, J. Maxwell, G. Mbianda, D. Meekins, M. Meziane, J. Miller, A. Mkrtchyan, H. Mkrtchyan, J. Mulholland, V. Nelyubin, L. Pentchev, C. F. Perdrisat, E. Piasetzky, Y. Prok, A. J. R. Puckett, V. Punjabi, M. Shabestari, A. Shahinyan, K. Slifer, G. Smith, P. Solvignon, R. Subedi, F. R. Wesselmann, S. Wood, Z. Ye, X. Zheng

**Category:**Nuclear Experiment

Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7~GeV at a proton scattering angle of \cma$= 70^\circ$. Read More

**Affiliations:**

^{1}ITA, S. Jose' dos Campos, Brazil,

^{2}INFN Rome, Italy,

^{3}INFN Pisa, Italy

For the first time, the inhomogeneous Bethe-Salpeter Equation for an interacting system, composed by two massive scalars exchanging a massive scalar, is numerically investigated in ladder approximation, directly in Minkowski space, by using an approach based on the Nakanishi integral representation. In this paper, the limiting case of zero-energy states is considered, extending the approach successfully applied to bound states. The numerical values of scattering lengths, are calculated for several values of the Yukawa coupling constant, by using two different integral equations that stem within the Nakanishi framework. Read More

The analysis of semi-inclusive deep inelastic electron scattering off polarized $^3$He at finite momentum transfers, aimed at the extraction of the quark transverse-momentum distributions in the neutron, requires the use of a distorted spin-dependent spectral function for $^3$He, which takes care of the final state interaction effects. This quantity is introduced in the non-relativistic case, and its generalization in a Poincar\'e covariant framework, in plane wave impulse approximation for the moment being, is outlined. Studying the light-front spin-dependent spectral function for a J=1/2 system, such as the nucleon, it is found that, within the light-front dynamics with a fixed number of constituents and in the valence approximation, only three of the six leading twist T-even transverse-momentum distributions are independent. Read More

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. Read More

**Affiliations:**

^{1}ITA, S. Jose' dos Campos,

^{2}INFN - Rome,

^{3}INFN - Pisa

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. Read More

**Affiliations:**

^{1}JINR,

^{2}Roma3 U.,

^{3}Tor Vergata U.,

^{4}INFN,

^{5}Perugia U.

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. Read More

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. Read More

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. Read More

**Affiliations:**

^{1}INFN -Roma,

^{2}Tor Vergata Univ.,

^{3}Tor Vergata Univ.

**Category:**High Energy Physics - Phenomenology

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. Read More

**Affiliations:**

^{1}CTA-São José dos Campos,

^{2}INFN-Rome,

^{3}INFN - Pisa

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. Read More

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. Read More

The Relativistic Distorted-Wave Impulse Approximation is used to describe the $^3$He($e,e^\prime p$)$^2$H process. We describe the $^3$He nucleus within the adiabatic hyperspherical expansion method with realistic nucleon-nucleon interactions. The overlap between the $^3$He and the deuteron wave functions can be accurately computed from a three-body calculation. Read More

**Affiliations:**

^{1}ITA - S. José dos Santos,

^{2}ITA and Coimbra Univ.,

^{3}Rome Univ. "Tor Vergata" and INFN,

^{4}INFN - Rome

**Category:**High Energy Physics - Phenomenology

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. Read More

**Affiliations:**

^{1}ITA- S. Jose' dosCampos,

^{2}Rome Univ. "Tor Vergata" and INFN,

^{3}IPN - Orsay,

^{4}INFN-Rome

**Category:**High Energy Physics - Phenomenology

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. Read More

**Affiliations:**

^{1}Rome Univ."Tor Vergata" and INFN,

^{2}Univer. Cruzeiro do Sul,

^{3}ITA, S. Jose' dos Campos,

^{4}IN2P3 Orsay,

^{5}INFN-Rome

**Category:**High Energy Physics - Phenomenology

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. Read More

**Affiliations:**

^{1}ITA - S. Jose' dos Campos,

^{2}Rome Univ. "Tor Vergata and INFN,

^{3}Pavia Univ.,

^{4}INFN - Rome

**Category:**High Energy Physics - Phenomenology

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. Read More

**Affiliations:**

^{1}Sao Paulo, Inst. Tech. Aeronautics,

^{2}Roma U., Tor Vergata & INFN, Roma2,

^{3}Pavia U. & INFN, Pavia,

^{4}INFN, Roma

**Category:**High Energy Physics - Phenomenology

The generalized parton distributions of the pion are studied within different light-front approaches for the quark-hadron and quark-photon vertices, exploring different kinematical regions in both the valence and non-valence sector. Moments of the generalized parton distributions which enter the definition of generalized form factors are also compared with recent lattice calculations. Read More

**Affiliations:**

^{1}ITA-CTA,

^{2}Tor Vergata Unv.,

^{3}Pavia Unv.,

^{4}INFN-Rome

**Category:**High Energy Physics - Phenomenology

We investigate the model dependence of no-helicity flip generalized parton distribution of the pion upon different approaches for the quark-hadron and quark-photon vertexes, in the spacelike region. In order to obtain information on contributions from both the valence and non-valence regions, we compare results for spacelike momentum transfers obtained from i) an analytic covariant model with a bare quark-photon vertex, ii) a Light-front approach with a quark-photon vertex dressed through a microscopic vector-meson model and iii) a Light-front approach based on the Relativistic Hamiltonian Dynamics. Our comparisons lead to infer the same dynamical mechanism, the one-gluon-exchange dominance at short distances, as a source of both the electromagnetic form factor at large momentum transfer and the parton distribution close to the end-points. Read More

**Affiliations:**

^{1}INFN - Rome

**Category:**High Energy Physics - Phenomenology

Some recent advances in the theoretical description of the Nucleon electromagnetic form factors, both in the space- and time-like regions, will be briefly illustrated. In particular, both the present stage of the lattice calculations and updated phenomenological approaches, like the ones based on dispersion relations and on microscopical models, will be reported. Read More

**Affiliations:**

^{1}CCET, U. Cruzeiro do Sul,

^{2}ITA, S. Josè dos Campos,

^{3}U. of Rome "Tor Vegata", INFN-TVG,

^{4}U. of Rome "Sapienza",

^{5}INFN - Roma

**Category:**High Energy Physics - Phenomenology

For the first time, a phenomenological analysis of the experimental electromagnetic form factors of the nucleon, both in the timelike and spacelike regions, is performed by taking into account the effects of nonvalence components in the nucleon state, within a light-front framework. Our model, based on suitable Ansatzes for the nucleon Bethe-Salpeter amplitude and a microscopic version of the well-known Vector Meson Dominance model, has only four free parameters (determined by the spacelike data with $\chi^2/datum \sim 1.7$), and yields a nice description of the experimental electromagnetic form factors in the physical region in the range $-30 (GeV/c)^2 < q^2 < 20 (GeV/c)^2$, except for the neutron one in the timelike region. Read More

**Authors:**E94010 Collaboration, K. Slifer, M. Amarian, L. Auerbach, T. Averett, J. Berthot, P. Bertin, B. Bertozzi, T. Black, E. Brash, D. Brown, E. Burtin, J. Calarco, G. Cates, Z. Chai, J. -P. Chen, Seonho Choi, E. Chudakov, C. Ciofi degli Atti, E. Cisbani, C. W. de Jager, A. Deur, R. DiSalvo, S. Dieterich, P. Djawotho, M. Finn, K. Fissum, H. Fonvieille, S. Frullani, H. Gao, J. Gao, F. Garibaldi, A. Gasparian, S. Gilad, R. Gilman, A. Glamazdin, C. Glashausser, W. Glockle, J. Golak, E. Goldberg, J. Gomez, V. Gorbenko, J. -O. Hansen, B. Hersman, R. Holmes, G. M. Huber, E. Hughes, B. Humensky, S. Incerti, M. Iodice, S. Jensen, X. Jiang, C. Jones, G. Jones, M. Jones, C. Jutier, H. Kamada, A. Ketikyan, I. Kominis, W. Korsch, K. Kramer, K. Kumar, G. Kumbartzki, M. Kuss, E. Lakuriqi, G. Laveissiere, J. J. Lerose, M. Liang, N. Liyanage, G. Lolos, S. Malov, J. Marroncle, K. McCormick, R. D. McKeown, Z. -E. Meziani, R. Michaels, J. Mitchell, A. Nogga, E. Pace, Z. Papandreou, T. Pavlin, G. G. Petratos, D. Pripstein, D. Prout, R. Ransome, Y. Roblin, D. Rowntree, M. Rvachev, F. Sabatie, A. Saha, G. Salme, S. Scopetta, R. Skibinski, P. Souder, T. Saito, S. Strauch, R. Suleiman, K. Takahashi, S. Teijiro, L. Todor, H. Tsubota, H. Ueno, G. Urciuoli, R. Van der Meer, P. Vernin, H. Voskanian, H. Witala, B. Wojtsekhowski, F. Xiong, W. Xu, J. -C. Yang, B. Zhang, P. Zolnierczuk

**Category:**Nuclear Experiment

We present a measurement of the spin-dependent cross sections for the \vec{^3He}(\vec{e},e')X} reaction in the quasielastic and resonance regions at four-momentum transfer 0.1 < Q^2< 0.9 GeV^2. Read More

**Affiliations:**

^{1}CETEC, Universidade Cruzeiro do Sul, UNICSUL,

^{2}CETEC, Universidade Cruzeiro do Sul, UNICSUL,

^{3}Universita di Roma Tour Vergata, Rome, Italy,

^{4}Universita di Roma Tour Vergata, Rome, Italy,

^{5}INFN, Rome, Italy

We carefully investigate the reliability of the propagator Pole Approximation, i.e, the approximation of retaining only the propagator in the evaluation of the Mandelstam covariant expression for the eletromagnetic current of the pion. Different frames are analyzed, in order to find the most suitable one for calculating the pion form factor within the proposed approximation. Read More

Investigation of the spacelike and timelike electromagnetic form factors of hadrons, within a relativistic microscopical model characterized by a small set of hypothesis, could shed light on the components of hadron states beyond the valence one. Our relativistic approach has been successfully applied first to the pion and then the extension to the nucleon has been undertaken. The pion case is shortly reviewed as an illustrative example for introducing the main ingredients of our approach, and preliminary results for the nucleon in the spacelike range $-10 (GeV/c)^2\le q^2 \le 0$ are evaluated. Read More

**Affiliations:**

^{1}Centro de Ciências Exatas e Tecnológicas, Universidade Cruzeiro do Sul, Sao Paulo, SP., and Instituto de Fisica Teorica, Universidade Estadual Paulista, SP, Brazil,

^{2}Dep. de Fisica, Instituto Tecnologico da Aeronautica, Centro Tecnico Aeroespacial, Sao Jose dos Campos, SP., Brazil,

^{3}Dipartimento di Fisica, Universita di Roma "Tor Vergata" and Istituto Nazionale di Fisica Nucleare, Sezione Tor Vergata, Via della Ricerca Scientifica 1, Roma, Italy,

^{4}Istituto Nazionale di Fisica Nucleare, Sezione Roma I, P.le A. Moro 2, Roma, Italy

The simultaneous investigation of the pion electromagnetic form factor in the space- and time-like regions within a light-front model allows one to address the issue of non-valence components of the pion and photon wave functions. Our relativistic approach is based on a microscopic vector meson dominance (VMD) model for the dressed vertex where a photon decays in a quark-antiquark pair, and on a simple parametrization for the emission or absorption of a pion by a quark. The results show an excellent agreement in the space like region up to -10 $(GeV/c)^2$, while in time-like region the model produces reasonable results up to 10 $(GeV/c)^2$. Read More

**Affiliations:**

^{1}Instituto de Fisica Teorica, IFT, UNESP, SP., Brazil and Centro de Ciencias Exatas e Tecnologicas, Universidade Cruzeiro do Sul, Sao Paulo, SP., Brazil,

^{2}Dep. de Fisica, ITA, CTA, Sao Jose dos Campos, SP., Brazil,

^{3}Dipartimento di Fisica, Universita di Roma Tor Vergata, and INFN Sezione Tor Vergata, Roma, Italy,

^{4}Universita de Roma I, INFN, Roma, Italy

We present detailed numerical results for the pion space-like electromagnetic form factor obtained within a recently proposed model of the pion electromagnetic current in a confining light-front QCD-inspired model. The model incorporates the vector meson dominance mechanism at the quark level, where the dressed photon with $q^+>0$ decay in an interacting quark-antiquark pair,wich absorbs the initial pion and produces the pion in the final state. Read More

**Affiliations:**

^{1}Instituto de Fisica Teorica, UNESP, Sao Paulo, SP, Brazil,

^{2}Dep. de Fisica, ITA, CTA, Sao Jose dos Campos, Sao Paulo, Brazil,

^{3}Dipartimento di Fisica, Universita di Roma "Tor Vergata" and Istituto Nazionale di Fisica Nucleare, Sezione Tor Vergata, Roma, Italy,

^{4}Istituto Nazionale di Fisica Nucleare, Roma, Italy

The frame dependence of the pair-term contribution to the electromagnetic form factor of the pion is studied within the Light Front approach. A symmetric ansatz for the pion Bethe-Salpeter amplitude with a pseudo scalar coupling of the constituent to the pion field is used. In this model, the pair term vanishes for the Drell-Yan condition, while it is dominant for momentum transfer along the light-front direction. Read More

The momentum distributions of the constituent quarks inside the nucleon and the prominent electroproduced nucleon resonances are investigated in the two most sophisticated, available quark potential models, based respectively on the assumption of the valence + gluon dominance and on the exchange of the pseudoscalar Goldstone-bosons arising from the spontaneous breaking of chiral symmetry. It is shown that both models predict a large, similar content of high-momentum components, due to the short-range part of the interquark interaction, which affect the behaviour of both elastic and transition electromagnetic form factors at large values of the momentum transfer. The electromagnetic form factors are calculated within a relativistic approach formulated on the light-front, adopting a one-body current with constituent quark form factors. Read More

The parameter-free predictions for the $N - P_{11}(1440)$ and $N - P_{33}(1232)$ electromagnetic transition form factors, obtained within our light-front constituent quark model using eigenfunctions of a baryon mass operator which includes a large amount of configuration mixing, are reported. The effects due to small components in the baryon wave functions, such as S'- and D-wave, are also investigated. Read More

A parameter-free evaluation of the $N - P_{11}(1440)$ electromagnetic transition form factors is performed within a light-front constituent quark model, using for the first time the eigenfunctions of a mass operator which generates a large amount of configuration mixing in baryon wave functions. A one-body electromagnetic current, which includes the phenomenological constituent quark form factors already determined from an analysis of pion and nucleon experimental data, is adopted. For $Q^2$ up to few $(GeV/c)^2$, at variance with the enhancement found in the elastic channel, the effect of configuration mixing results in a significant suppression of the calculated helicity amplitudes with respect to both relativistic and non-relativistic calculations, based on a simple gaussian-like ansatz for the baryon wave functions. Read More

The elastic and transition electromagnetic form factors of mesons are investigated within a light-front constituent quark model. The general formulae for the space-like matrix elements of the one-body component of the electromagnetic current, including both Dirac and Pauli form factors of the constituent quarks, are presented. Our results for the pion charge form factor and the $\pi \rho$ transition form factor are reported and compared with those obtained within various relativistic approaches in a range of values of the four-momentum transfer accessible to $CEBAF$. Read More

We have evaluated nucleon and pion electromagnetic form factors using for the first time eigenfunctions of a light-front mass operator, reproducing a large set of energy levels, and constituent quark form factors in the one-body current. The comparison with the experimental data yields valuable information on the electromagnetic structure of light constituent quarks and on the different role played by their Dirac and Pauli form factors. Read More

A parameter-free evaluation of the $N - \Delta$ electromagnetic transition form factors is carried out in a light-front constituent quark model, based on $N$ and $\Delta$ eigenstates of a mass operator which reproduces a large set of hadron energy levels. A one-body electromagnetic current, including the constituent quark form factors previously determined within the same approach from nucleon and pion experimental data, is used. Our prediction for the magnetic transition form factor is compared with the results both of phenomenological analyses of experimental data for the $\Delta$ electroproduction, and of an analysis which includes the effects of off-energy-shell $\pi - N$ final state interaction. Read More

The form factors of the $\pi \rho$ and $\pi \omega$ radiative transitions are evaluated within a light-front constituent quark model, using for the first time the eigenfunctions of a light-front mass operator reproducing the meson mass spectrum and including phenomenological Dirac and Pauli quark form factors in the one-body electromagnetic current operator. The sensitivity of the transition form factors both to the meson wave functions and to the constituent quark form factors is illustrated. It is shown that the measurement of the $\pi \rho$ and $\pi \omega$ radiative transitions could help in discriminating among various models of the meson structure. Read More

The charge form factor of $\pi$ and $K$ mesons is evaluated adopting a relativistic constituent quark model based on the light-front formalism. The relevance of the high-momentum components of the meson wave function, for values of the momentum transfer accessible to $CEBAF$ energies, is illustrated. The predictions for the elastic form factor of $\pi$ and $K$ mesons are compared with the results of different relativistic approaches, showing that the measurements of the pion and kaon form factors planned at $CEBAF$ could provide information for discriminating among various models of the meson structure. Read More

Nucleon and pion electromagnetic form factors are evaluated in the spacelike region within a light-front constituent quark model, where eigenfunctions of a mass operator, reproducing a large set of hadron energy levels, are adopted and quark form factors are considered in the one-body current. The hadron form factors are sharply affected by the high momentum tail generated in the wave function by the one-gluon-exchange interaction. Useful information on the electromagnetic structure of light constituent quarks can be obtained from the comparison with nucleon and pion experimental data. Read More

The electromagnetic form factors of the $\rho$ meson are evaluated adopting a relativistic constituent quark model based on the light-front formalism, and using a meson wave function with the high-momentum tail generated by the one-gluon-exchange interaction. The breakdown of the rotational covariance for the one-body component of the current operator is investigated and the sensitivity of the ratio of the $\rho$-meson form factors to the pion (charge) form factor to the spin-dependent component of the effective $q \bar{q}$ interaction is illustrated. Read More

The theory of quasi-elastic inclusive scattering of polarized leptons off polarized $^3$He is critically reviewed and the origin of different expressions for the polarized nuclear response function appearing in the literature is explained. The sensitivity of the longitudinal asymmetry upon the neutron form factors is thoroughly investigated and the role played by the polarization angle for minimizing the proton contribution is illustrated. Read More

The high momentum components generated in the wave function of pseudoscalar mes* by the one-gluon-exchange interaction are investigated within a relativistic constituent quark model. Adopting the light-cone formalism, the sensitivity of the weak decay constant and the charge form factor to hard constituent quarks is illustrated. Read More

We show the equivalence of a previously derived exact expression for the response of a non-relativistic system with harmonic forces and an infinite sum of weighted $\delta$-functions corresponding to the spectrum. We forward arguments, indicating that the Gersch-Rodriguez-Smith $1/q$-expansion of the response does not converge and prove that this expansion is an asymptotic series. Read More

A comprehensive treatement of the theoretical approach for describing nuclear effects in inclusive scattering of polarized electrons by polarized $^3$He is presented. Read More