Rho-omega Mixing and the Pion Electromagnetic Form-Factor

An improved update of the structure and decays of $\rho^0$, $\omega$ and $\phi$ mesons based on a chiral SU(3) Lagrangian, including anomaly terms is presented. We demonstrate that a consistent and quantitatively successful description of both pion and kaon electromagnetic form factors can be achieved. We also discuss the $e^+e^- \to \pi^+ \pi^0 \pi^-$ cross section, the Dalitz decay $\omega \to \pi^0 \mu^+ \mu^-$ and aspects of $\rho^0 \omega$ and $\omega \phi$ mixing. Relat...

A way to explain the puzzling difference between the pion form factor as measured in e+ e- annihilations and in tau decays is discussed. We show that isospin symmetry breaking, beside the already identified effects, produces also a full mixing between the rho0, omega and phi mesons which generates an isospin 0 component inside the rho0 meson. This effect, not accounted for in current treatments of the problem, seems able to account for the apparent mismatch between e+ e- and ...

We study the self-energy amplitudes for the rho-omega meson system produced by an effective field theory model at the quark level characterized by a finite range quark-quark interaction and an isospin breaking bare quark mass difference $m_u - m_d$. Dynamical effects associated with confinement and dressing of quarks and the finite size of the produced $\bar{q}q$ meson modes are treated. Parameters of this approach, previously constrained by soft pion physics, are here supple...

We use the 1/N_c method to estimate electromagnetic contributions to vector meson masses and mixings. We identify several new sources of rho-omega mixing coming from short-distance effects. We comment on the extraction of quark masses from the vector meson masses. We also present a simple group theoretical discussion of the electromagnetic mass differences.

We present our calculations of the electromagnetic form factor of pions. We explore the properties of pion form factor at momentum transfer larger than previous studies by including more combinations of source and sink momenta and using more configurations.We fit our results using vector meson dominance (VMD) hypothesis.

In this talk, we introduce an effective chiral action, derived from the instanton QCD vacuum configuration, in order to study the modification of mesonic properties in medium. We present our recent theoretical results on the electromagnetic from factor and rho-meson mass shift at finite density. We observe that the rho-meson mass is dropped by about 10%: m*_rho/m_rho ~ 1-0.12 mu_B/mu_0, which is compatible with that estimated by the QCD sum rule as well as by Brown and Rho.

Contributions of two-pseudoscalar and vector-pseudoscalar meson loops to the rho-omega mass splitting are evaluated in a covariant model based on studies of the Schwinger-Dyson equations of QCD. The role and importance of the different time orderings of the meson loops is analyzed and compared with those obtained within time-ordered perturbation theory. It is shown that each meson loop contributes less than 10% of the bare mass, and decreases as the masses of the intermediate...

Having calculated the light-cone wave function of the pseudoscalar meson by using two equivalent and fully covariant methods, we generalize such methods to the valence Fock states of the vector meson in the light-cone formalism. We investigate the decay constant of the $\rho$ meson $f_{\rho}$, the $\gamma^{\ast} \pi \to \rho $ and $\gamma^* \rho \to \pi $ transition form factors and especially the transition magnetic moments. By using two groups of constraint parameters, we p...

The pion electromagnetic form factor and two-pion production in electron-positron collisions are simultaneously fitted by a vector dominance model evolving to perturbative QCD at large momentum transfer. This model was previously successful in simultaneously fitting the nucleon electromagnetic form factors (spacelike region) and the electromagnetic production of nucleon-antinucleon pairs (timelike region). For this pion case dispersion relations are used to produce the analyt...

We study a model-independent parameterization of the vector pion form factor that arises from the constraints of analyticity and unitarity. Our description should be suitable up to s^(1/2) ~ 1.2 GeV and allows a model-independent determination of the mass of the rho(770) resonance. We analyse the experimental data on tau^- -> pion^- pion^0 nu_tau and e^+ e^- -> pion^+ pion^- in this framework, and its consequences on the low-energy observables worked out by chiral perturbatio...