Deuteron Electromagnetic Properties with a Poincar\'e-Covariant Current Operator within Front-Form Hamiltonian Dynamics

Deuteron elastic and deep inelastic electromagnetic properties have been studied within the front-form Hamiltonian dynamics, using a Poincar\'e-covariant current operator. The deuteron elastic form factors are strongly sensitive to different realistic $N-N$ interactions, while the relevance of different nucleon form factor models is huge for $A(Q^2)$, weak for $B(Q^2)$ and negligible for the tensor polarization. The possibility to gain information on the neutron charge form factor from an analysis of $A(Q^2)$ has been investigated. The extraction of the neutron structure functions from the deuteron deep inelastic structure functions at high $x$ is largely affected by the use of our Poincar\'e-covariant relativistic approach instead of the usual impulse approximation within an instant-form approach.Comment: 12 pages, World-Scientific macro included. Proc. VIII Conf. on "Problems in Theoretical Nuclear Physics", Cortona (Italy) Oct. 18-20, 2000. (World Scientific, Fall 2001

Solving the inhomogeneous Bethe-Salpeter Equation in Minkowski space: the zero-energy limit

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. Those low-energy observables are compared with (i) the analogous quantities recently obtained in literature, within a totally different framework and (ii) the non relativistic evaluations, for illustrating the relevance of a non perturbative, genuine field theoretical treatment in Minkowski space, even in the low-energy regime. Moreover, dynamical functions, like the Nakanishi weight functions and the distorted part of the zero-energy Light-front wave functions are also presented. Interestingly, a highly non trivial issue related to the abrupt change in the width of the support of the Nakanishi weight function, when the zero-energy limit is approached, is elucidated, ensuring a sound basis to the forthcoming evaluation of phase-shifts.Comment: 23 pages and 4 figures. Minor changes in the abstract, typos fixed and added a figure. Submitted for publicatio

Neutron unpolarized structure function F_2^n(x) from deep inelastic scattering off ^{3}He and ^{3}H

The possibility to safely extract the neutron deep inelastic structure function $F_2^n(x)$ in the range $0 \le x \le 0.9$ from joint measurements of deep inelastic structure functions of $^{3}He$ and $^{3}H$ is demonstrated. While the nuclear structure effects are relevant, the model dependence in this extraction linked to the $N-N$ interaction is shown to be weak.Comment: 5 pages. Proc. XVIIth Conf. on "Few-Body Problems in Physics", Evora( Portugal) Sept. 11, 2000. To appear in Nucl. Phys.

A Study of Final State Effects in the electrodisintegration of a polarized Helium-3 target

An approach for the description of the final state interaction in the evaluation of inclusive electromagnetic responses of a polarized Helium-3 target, is briefly illustrated. Preliminary results of calculations, where the final state interaction is fully taken into account for the two-body break-up channel, are compared with experimental data, showing a very encouraging improvement with respect to the plane wave impulse approximation results.Comment: 8 pages. Proc. of "GDH 2004", Old Dominion University, Norfolk, Va, June 2-5, 2004. Class file "ws-procs9x6.cls" and style file "rotating_pr.sty" include

Pion Generalized Parton Distributions within a fully covariant constituent quark model

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.Comment: Pages 20, figure 11 and table 8. Minor changes. To be published in EPJ

Probing the parton content of the nucleon

The parton content of the nucleon is explored within a meson-cloud model developed to derive light-cone wave functions for the physical nucleon. The model is here applied to study electromagnetic form factors, distribution amplitudes and nucleon-to-meson transition distribution amplitudes.Comment: 10 pages, 6 figures; proceedings of the workshop "Recent Advances in Perturbative QCD and Hadronic Physics" in Honor of Prof. Anatoly Efremov's 75th Birthday Celebration; to appear in Mod. Phys. Lett.