14,143 research outputs found
Spin-1 Particle in the Light-Front Approach
The electromagnetic current of spin-1 composite particles does not transform
properly under rotations if only the valence contribution is considered in the
light-front model. In particular, the plus component of the current, evaluated
only for the valence component of the wave function, in the Drell-Yan frame
violates rotational symmetry, which does not allow a unique calculation of the
electromagnetic form-factors. The prescription suggested by Grach and
Kondratyuk [Sov. J. Nucl. Phys. 38, 198 (1984)] to extract the form factors
from the plus component of the current, eliminates contributions from pair
diagrams or zero modes, which if not evaluated properly cause the violation of
the rotational symmetry. We address this problem in an analytical and covariant
model of a spin-1 composite particle.Comment: To appear Brazilian Journal of Physics (2004), 4 pages, no figures.
Use multicols.st
Light-Front projection of spin-1 electromagnetic current and zero-modes
The issue of the contribution of zero-modes to the light-front projection of
the electromagnetic current of phenomenological models of vector particles
vertices is addressed in the Drell-Yan frame. Our analytical model of the
Bethe-Salpeter amplitude of a spin-1 fermion-antifermion composite state gives
a physically motivated light-front wave function symmetric by the exchange of
the fermion and antifermion, as in the -meson case. We found that among
the four independent matrix elements of the plus component in the light-front
helicity basis only the one carries zero mode contributions. Our
derivation generalizes to symmetric models, important for applications, the
above conclusion found for a simplified non-symmetrical form of the spin-1
Bethe-Salpeter amplitude with photon-fermion point-like coupling and also for a
smeared fermion-photon vertex model.Comment: Use elservier style. 14 page
A combined study of the pion's static properties and form factors
We study consistently the pion's static observables and the elastic and
\gamma*\gamma -> \pi^0 transition form factors within a light-front model.
Consistency requires that all calculations are performed within a given model
with the same and single adjusted length or mass-scale parameter of the
associated pion bound-state wave function. Our results agree well with all
extent data including recent Belle data on the \gamma*\gamma -> \pi^0 form
factor at large q^2, yet the BaBar data on this transition form factor resists
a sensible comparison. We relax the initial constraint on the bound-state wave
function and show the BaBar data can partially be accommodated. This, however,
comes at the cost of a hard elastic form factor not in agreement with
experiment. Moreover, the pion charge radius is about 40% smaller than its
experimentally determined value. It is argued that a decreasing charge radius
produces an ever harder form factor with a bound-state amplitude difficultly
reconcilable with soft QCD. We also discuss why vector dominance type models
for the photon-quark vertex, based on analyticity and crossing symmetry, are
unlikely to reproduce the litigious transition form factor data.Comment: 14 pages, 7 figures, 2 Tables; minor changes; 2 new references added
(Ref. 54 and 57); version to be published in Few Body Physic
Light-front model of the kaon electromagnetic current
The electromagnetic form factor is extracted from both components of the
electromagnetic current: J(plus) and J(minus) with a pseudo-scalar coupling of
the quarks to the kaon.
In the case of J(plus) there is no pair term contribution in the Drell-Yan
frame. However, J(minus) component of the electromagnetic current the pair term
contribution is different from zero and is necessary include it to preserve the
rotational symmetry of the current.Comment: 4 pages, 1 figure, uses World Scientific style file. To be published
by World Scientific in the proceedings of the "VIII International Workshop on
Hadron Physics,(HADRONS 2002)", Bento Goncalves, RS, Brazi
Relativistic dynamics of Qqq systems
The bound state of constituent quarks forming a composite baryon is
investigated in a QCD-inspired effective light-front model. The light-front
Faddeev equations are derived and solved numerically. The masses of the spin
1/2 low-lying states of the nucleon, , and
are found and compared to the experimental data. The data is
qualitatively described with a flavor independent effective interaction.Comment: 18 pages, include 6 figures, 2 eps figures, use latex, revtex. To
appear Phys. Rev D (2002
Ground State Masses and Biding Energies of the Nucleon, Hyperon and Heavy Baryons in a Light-Front Model
The ground state masses and binding energies of the nucleon,
, , are studied within a constituent
quark QCD-inspired light-front model. The light-front Faddeev equations for the
composite spin 1/2 baryons, are derived and solved numerically. The
experimental data for the masses are qualitatively described by a flavor
independent effective interaction.Comment: 13 pages, include 4 eps figures, use latex, revte
The pion electromagnetic form-factor in a QCD-inspired model
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 decay in an interacting quark-antiquark
pair,wich absorbs the initial pion and produces the pion in the final state.Comment: Talk given in Light-Cone 2004, Amsterdam,NL., 16-20 August, 2004. To
appear in "Few-Body Systems". 4 pages, 2 figues eps, use Few-Body Sytems
latex styl
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