9 research outputs found
Electromagnetic form factors of light vector mesons
The electromagnetic form factors G_E(q^2), G_M(q^2), and G_Q(q^2), charge
radii, magnetic and quadrupole moments, and decay widths of the light vector
mesons rho^+, K^{*+} and K^{*0} are calculated in a Lorentz-covariant,
Dyson-Schwinger equation based model using algebraic quark propagators that
incorporate confinement, asymptotic freedom, and dynamical chiral symmetry
breaking, and vector meson Bethe-Salpeter amplitudes closely related to the
pseudoscalar amplitudes obtained from phenomenological studies of pi and K
mesons. Calculated static properties of vector mesons include the charge radii
and magnetic moments: r_{rho+} = 0.61 fm, r_{K*+} = 0.54 fm, and r^2_{K*0} =
-0.048 fm^2; mu_{rho+} = 2.69, mu_{K*+} = 2.37, and mu_{K*0} = -0.40. The
calculated static limits of the rho-meson form factors are similar to those
obtained from light-front quantum mechanical calculations, but begin to differ
above q^2 = 1 GeV^2 due to the dynamical evolution of the quark propagators in
our approach.Comment: 8 pages of RevTeX, 5 eps figure
Bethe-Salpeter Approach for Unitarized Chiral Perturbation Theory
The Bethe-Salpeter equation restores exact elastic unitarity in the
channel by summing up an infinite set of chiral loops. We use this equation to
show how a chiral expansion can be undertaken in the two particle irreducible
amplitude and the propagators accomplishing exact elastic unitarity at any
step. Renormalizability of the amplitudes can be achieved by allowing for an
infinite set of counter-terms as it is the case in ordinary Chiral Perturbation
Theory. Crossing constraints can be imposed on the parameters to a given order.
Within this framework, we calculate the leading and next-to-leading
contributions to the elastic scattering amplitudes, for all isospin
channels, and to the vector and scalar pion form factors in several
renormalization schemes. A satisfactory description of amplitudes and form
factors is obtained. In this latter case, Watson's theorem is automatically
satisfied. From such studies we obtain a quite accurate determination of some
of the ChPT low energy parameters ({\bar l}_1 - {\bar l}_2 =
-6.1\er{0.1}{0.3} and ). We also compare the two
loop piece of our amplitudes to recent two--loop calculations.Comment: 63 pages, 9 figures. Some discussions on off-shell ambiguities and
convergence of the expansion adde
Electromagnetic Meson Form Factors in the Salpeter Model
We present a covariant scheme to calculate mesonic transitions in the
framework of the Salpeter equation for -states. The full Bethe
Salpeter amplitudes are reconstructed from equal time amplitudes which were
obtained in a previous paper\cite{Mue} by solving the Salpeter equation for a
confining plus an instanton induced interaction. This method is applied to
calculate electromagnetic form factors and decay widths of low lying
pseudoscalar and vector mesons including predictions for CEBAF experiments. We
also describe the momentum transfer dependence for the processes
.Comment: 22 pages including 10 figure