Extracting Br(omega->pi^+ pi^-) from the Time-like Pion Form-factor

We extract the G-parity-violating branching ratio Br(omega->pi^+ pi^-) from the effective rho-omega mixing matrix element Pi_{rho omega}(s), determined from e^+e^- -> pi^+ pi^- data. The omega->pi^+ pi^- partial width can be determined either from the time-like pion form factor or through the constraint that the mixed physical propagator D_{rho omega}^{mu nu}(s) possesses no poles. The two procedures are inequivalent in practice, and we show why the first is preferred, to find finally Br(omega->pi^+ pi^-) = 1.9 +/- 0.3%.Comment: 12 pages (published version

Higher meson resonances in ρ→π0π0γ\rho \to \pi^0 \pi^0 \gamma and ω→π0π0γ\omega \to \pi^0 \pi^0 \gamma

The role of higher meson resonances with spin 1 and 2 is investigated quantitatively in the decay processes of $\rho \to \pi^0\pi^0 \gamma$ and $\omega \to \pi^0 \pi^0 \gamma$. Among the higher resonances, we find that the $f_2(1270)$ tensor meson can give a nontrivial contribution especially to the $\omega \to \pi^0 \pi^0 \gamma$ decay process. When the $f_2$ contribution is combined with the processes involving the vector and scalar meson intermediate states, a good agreement with the recent measurements is achieved for both decays. The effect of the $f_2(1270)$ is found to be sizable at the intermediate photon energies and may be verified by precise measurements of the recoil photon spectrum of the $\omega \to \pi^0 \pi^0 \gamma$ decay. The dependence of the decay widths on various models for the $\rho$-$\omega$ mixing in the literature is also investigated.Comment: 16 pages, REVTeX, 6 figures, revised version, to appear in Phys. Rev.

The Dipion Mass Spectrum In e+e- Annihilation and tau Decay: A Dynamical (rho0, omega, phi) Mixing Approach

We readdress the problem of finding a simultaneous description of the pion form factor data in e+e- annihilations and in tau decays. For this purpose, we work in the framework of the Hidden Local Symmetry (HLS) Lagrangian and modify the vector meson mass term by including the pion and kaon loop contributions. This leads us to define the physical rho, omega and phi fields as linear combinations of their ideal partners, with coefficients being meromorphic functions of s, the square of the 4--momentum flowing into the vector meson lines. This allows us to define a dynamical, i.e. s-dependent, vector meson mixing scheme. The model is overconstrained by extending the framework in order to include the description of all meson radiative (V P gamma and P gamma gamma couplings) and leptonic (Ve+e- couplings) decays and also the isospin breaking (omega/ phi --> pi+ pi-) decay modes. The model provides a simultaneous, consistent and good description of the e+e- and tau dipion spectra. The expression for pion form factor in the latter case is derived from those in the former case by switching off the isospin breaking effects specific to e+e- and switching on those for tau decays. Besides, the model also provides a good account of all decay modes of the form V P gamma, Pgamma gamma as well as the isospin breaking decay modes. It leads us to propose new reference values for the rho^0 --> e+ e- and omega --> pi+ pi- partial widths which are part of our description of the pion form factor. Other topics (phi --> K anti K, the rho meson mass and width parameters) are briefly discussed. Therefore, we confirm the 3.3 sigma discrepancy between the theoretical estimate of a_mu based on e+e- and its direct BNL measurement.Comment: 71 pages, 8 figures. Accepted by EPJ C. Version 3: correct minor typos, minor changes spread out into the text. Extension of Sections 12.2 and 12.3.5 and introduction of the new Appendix

The Quark-Photon Vertex and the Pion Charge Radius

The rainbow truncation of the quark Dyson-Schwinger equation is combined with the ladder Bethe-Salpeter equation for the dressed quark-photon vertex to study the low-momentum behavior of the pion electromagnetic form factor. With model gluon parameters previously fixed by the pion mass and decay constant, the pion charge radius $r_\pi$ is found to be in excellent agreement with the data. When the often-used Ball-Chiu Ansatz is used to construct the quark-photon vertex directly from the quark propagator, less than half of $r_\pi^2$ is generated. The remainder of $r^2_\pi$ is seen to be attributable to the presence of the $\rho$-pole in the solution of the ladder Bethe-Salpeter equation.Comment: 21 pages, 9 figure

J/Psi strong couplings to the vector mesons

We present a study of the cross sections J/Psi X --> D^(*) \bar D^(*) (X = rho, Phi) based on the calculation of the effective tri- and four-linear couplings J/Psi (X) D^(*) \bar D^(*) within a constituent quark model. In particular, the details of the calculation of the four-linear couplings J/Psi X D^(*)\bar D^(*) are given. The results obtained have been used in a recent analysis of J/Psi absorption by the hot hadron gas formed in peripheral heavy-ion collisions at SPS energies.Comment: 12 pages, 3 figure

Radiative Decays, Nonet Symmetry and SU(3) Breaking

We re-examine the problem of simultaneously describing in a consistent way all radiative and leptonic decays of light mesons (V -> P gamma, P -> V gamma, P -> gamma gamma, V -> e^+ e^-). For this purpose, we rely on the Hidden Local Symmetry model in both its anomalous and non--anomalous sectors. We show that the SU(3) symmetry breaking scheme proposed by Bando, Kugo and Yamawaki, supplemented with nonet symmetry breaking in the pseudoscalar sector, allows one to reach a nice agreement with all data, except for the K^{*+/-} radiative decay. An extension of this breaking pattern allows one to account for this particular decay mode too. Considered together, the whole set of radiative decays provides a pseudoscalar mixing angle theta_P ~ -11^o and a value for theta_V which is ~ 3^o from that of ideal mixing. We also show that it is impossible, in a practical sense, to disentangle the effects of nonet symmetry breaking and those of glue inside the eta', using only light meson decays.Comment: 36 pages. Published versio

ω−ρ\omega-\rho Mixing and the ω→ππγ\omega\to\pi\pi\gamma Decay

We reexamine the $\omega \to \pi^{0} \pi^{0} \gamma$ decay, adding the effect of $\omega-\rho$ mixing to the amplitude calculated with the aid of chiral perturbation theory and vector meson dominance. We predict the neutral decay to occur with a width of $\Gamma($\omega \to \pi^{0} \pi^{0} \gamma $) =(390\pm96) {\rm eV}$ and also analyze the effect of the $\omega-\rho$ mixing on the $\Gamma($\omega \to \pi^{0} \pi^{0} \gamma $)/ \Gamma($\omega \to \pi^{+} \pi^{-} \gamma $)$ ratio. Several remarks on the effect of $\omega-\rho$ mixing on certain radiative decays of vector mesons are presented.Comment: 10 pages, LaTeX, 1 ps-figure. Submitted to Phys. Rev.

Selected nucleon form factors and a composite scalar diquark

A covariant, composite scalar diquark, Fadde'ev amplitude model for the nucleon is used to calculate pseudoscalar, isoscalar- and isovector-vector, axial-vector and scalar nucleon form factors. The last yields the nucleon sigma-term and on-shell sigma-nucleon coupling. The calculated form factors are soft, and the couplings are generally in good agreement with experiment and other determinations. Elements in the dressed-quark-axial-vector vertex that are not constrained by the Ward-Takahashi identity contribute ~20% to the magnitude of g_A. The calculation of the nucleon sigma-term elucidates the only unambiguous means of extrapolating meson-nucleon couplings off the meson mass-shell.Comment: 12 pages, REVTEX, 5 figures, epsfi

Tri-meson-mixing of π\pi-η\eta-η′\eta' and ρ\rho-ω\omega-ϕ\phi in the light-cone quark model

The radiative transition form factors of the pseudoscalar mesons {$\pi$, $\eta$, $\eta'$} and the vector mesons {$\rho$, $\omega$, $\phi$} are restudied with $\pi$-$\eta$-$\eta'$ and $\rho$-$\omega$-$\phi$ in tri-meson-mixing pattern, which is described by tri-mixing matrices in the light-cone constituent quark model. The experimental transition decay widths are better reproduced with tri-meson-mixing than previous results in a two-mixing-angle scenario of only two-meson $\eta$-$\eta'$ mixing and $\omega$-$\phi$ mixing.Comment: 8 pages, 6 figures, final version to appear in EPJ

e+e- annihilation to (pi0 pi0 gamma) and (pi0 eta gamma) as a source of information on scalar and vector mesons

We present a general framework for the model-independent decomposition of the fully differential cross section of the reactions e+e- -> gamma* -> (pi0 pi0 gamma) and e+e- -> gamma* -> (pi0 eta gamma), which can provide important information on the properties of scalar mesons: f0(600), f0(980) and a0(980). For the model-dependent ingredients in the differential cross section, an approach is developed, which relies on Resonance Chiral Theory with vector and scalar mesons. Numerical results are compared to data. The framework is convenient for development of a Monte Carlo generator and can also be applied to the reaction e+e- -> gamma* -> (pi+ pi- gamma).Comment: 15 pages, 12 Figures, 4 Tables; LaTeX svjour style; update to the version accepted for publication in the European Physical Journal