E. Pace

Nucleon and pion electromagnetic form-factors in a light front constituent quark model

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.

Pair term in the Electromagnetic Current within the Front-Form Dynamics: Spin-0 Case

Abstract The frame and scale dependence of the pair-term contribution to the electromagnetic form factor of a spin-zero composite system of two-fermions is studied within the Light Front. The form factor is evaluated from the plus-component of the current in the Breit frame, using for the first time a nonconstant, symmetric ansatz for the Bethe–Salpeter amplitude. The frame dependence is analyzed by allowing a nonvanishing plus component of the momentum transfer, while the dynamical scale is set by the masses of the constituents and by mass and size of the composite system. Axa0transverse momentum distribution, associated with the Bethe–Salpeter amplitude, is introduced which allows to define strongly and weakly relativistic systems. In particular, for strongly relativistic systems, the pair term vanishes for the Drell–Yan condition, while is dominant for momentum transfer along the light-front direction. For a weakly relativistic system, fitted to the deuteron scale, the pair term is negligible up to momentum transfers of 1 (GeV/c)2. Axa0comparison with results obtained within the Front-Form Hamiltonian dynamics with a fixed number of constituents is also presented.

Pion generalized parton distributions with covariant and light-front constituent quark models

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 vertices, in the spacelike region. In order to obtain information on contributions from both the valence and the nonvalence 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 us 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. The expected collinear behavior of the generalized parton distributions at high-momentum transfer, i.e. a maximum for x{approx}1, is also illustrated, independently of the different approaches. Finally, a comparison with recent lattice calculations of the gravitational form factors is presented.

Spacelike and timelike pion electromagnetic form factor and Fock state components within the light-front dynamics

The simultaneous investigation of the pion electromagnetic form factor in the space- and timelike regions within a light-front model allows one to address the issue of nonvalence components of the pion and photon wave functions. Our relativistic approach is based on a microscopic vector-meson-dominance 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){sup 2}, while in timelike region the model produces reasonable results up to 10 (GeV/c){sup 2}.

THE NUCLEAR SCALING FUNCTION AND QUASI-ELASTIC ELECTRON SCATTERING BY NUCLEI

Abstract Inclusive electron scattering by nuclei at high momentum transfer is analysed in the impulsive approximation using fully relativistic kinematics, and an expression of the nuclear scaling function F (y) in terms of the spectral functions is obtained.

Electromagnetic form factor of the pion in the space- and time-like regions within the front-form dynamics

Abstract The pion electromagnetic form factor is calculated in the space- and time-like regions from −10xa0(GeV/ c ) 2 up to 10xa0(GeV/ c ) 2 , within a front-form model. The dressed photon vertex where a photon decays in a quark–antiquark pair is depicted generalizing the vector meson dominance ansatz, by means of the vector meson vertex functions. An important feature of our model is the description of the on-mass-shell vertex functions in the valence sector, for the pion and the vector mesons, through the front-form wave functions obtained within a realistic quark model. The theoretical results show an excellent agreement with the data in the space-like region, while in the time-like region the description is quite encouraging.

Charge form-factor of pi and K mesons

The charge form factor of

Neutron structure function F(2)**n (x) from deep inelastic electron scattering off few nucleon systems

ensuremath{pi}

Electroproduction of the Roper resonance and the constituent quark model

and

Charge form factor of {pi} and {ital K} mesons

K