Isgur-Wise form factors of heavy baryons within a light-front constituent quark model

The space-like elastic form factors of baryons containing a heavy quark are investigated within a light-front constituent quark model in the limit of infinite heavy-quark mass, adopting a gaussian-like ansatz for the three-quark wave function. The results obtained for the Isgur-Wise form factors corresponding both to a spin-0 and a spin-1 light spectator pair are presented. It is found that the Isgur-Wise functions depend strongly on the baryon structure, being sharply different in case of diquark-like or collinear-type configurations in the three-quark system. It is also shown that the relativistic effects lead to a saturation property of the form factors as a function of the baryon size. Our results are compared with those of different models as well as with recent predictions from QCD sum rules and lattice QCD simulations; the latter ones seem to suggest the dominance of collinear-type configurations, in which the heavy-quark is sitting close to the center-of-mass of the light quark pair.Comment: latex, 15 pp., 6 figures with epsfig.st

Light-front CQM calculations of baryon electromagnetic form factors

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.Comment: to appear in the Proceedings of the International Workshop on Hadron Dynamics with the new DAPHNE and CEBAF facilities, Frascati, Italy, 11-14 November 199

A light-front description of electromagnetic form factors for J≤3/2J \leq {3/2} hadrons

A review of the hadron electromagnetic form factors obtained in a light-front constituent quark model, based on the eigenfunctions of a mass operator, is presented. The relevance of different components in the q-q interaction for the description of hadron experimental form factors is analysed.Comment: 6 pages, Latex, 3 Postscript figures included. Proceedings of "Nucleon 99", Frascati, June 1999. To appear in Nucl. Phys.

Charge form factor of π\pi and KK mesons

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.Comment: 8 pages, latex, 4 figures available as separate .uu fil

Nucleon generalized polarizabilities within a relativistic Constituent Quark Model

Nucleon generalized polarizabilities are investigated within a relativistic framework, defining such quantities through a Lorentz covariant multipole expansion of the amplitude for virtual Compton scattering. The key physical ingredients in the calculation of the nucleon polarizabilities are the Lorentz invariant reduced matrix elements of the electromagnetic transition current, which can be evaluated from off-energy-shell helicity amplitudes. The evolution of the proton paramagnetic polarizability, $\beta_{para}(q)$, as a function of the virtual-photon three-momentum transfer $q,$ is explicitly evaluated within a relativistic constituent quark model by adopting transition form factors obtained in the light-front formalism. The discussion is focussed on the role played by the effects due to the relativistic approach and to the transition form factors, derived within different models.Comment: 14 pages and three figures (included), to appear in Phys. Rev. C (May 1998

Space-like and time-like 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 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 $(GeV/c)^2$.Comment: 74 pages, 11 figures, use revtex