We investigate ω–ϕ meson mixing to leading order in chiral perturbation theory utilizing the antisymmetric tensor field formulation. We update the quark mass ratio R from ρ–ω mixing, R = 42 ± 4.

We investigate the isovector axial vector and pseudoscalar form factors of ∆ baryon by employing light-cone QCD sum rules. Numerical calculations show that the form factors can be well fitted by the exponential form. We make a comparison with the predictions of lattice QCD, chiral perturbation theory and quark model.

We study the radiative decay φ → π 0 ηγ within the framework of a phenomenological approach in which the contributions of ρ-meson, chiral loop and a 0 -meson are considered. We analyze the interference effects between different contributions and utilizing the experimental branching ratio and invariant π 0 η mass spectrum for φ → π 0 ηγ decay we estimate the branching ratio of φ → a 0 γ decay.

In an attempt to explain the latest experimental result about the branching ratio of → 0 0 ␥ decay, we reexamine the mechanism of this decay in a phenomenological framework in which the contributions of vector meson dominance, chiral loops, -meson intermediate state amplitudes, and the effects ofmixing are considered. We conclude that in order to obtain the experimental value of the branching ratio B( → 0 0 ␥) the -meson amplitude, which makes a substantial contribution, should be included in the reaction mechanism and the effects ofmixing should be taken into account. We also estimate the coupling constant g ␥ as g ␥ ϭ0.11, which is much smaller than the values suggested by light cone QCD sum rule calculations.The recent experimental study of the → 0 0 ␥ and → 0 0 ␥ decays by the SND Collaboration obtained the value B(→ 0 0 ␥)ϭ(6.6 Ϫ0.8 ϩ1.4 Ϯ0.6)ϫ10 Ϫ5 for the branching ratio of the → 0 0 ␥ decay ͓1͔. Their result is in good agreement with the GAMS Collaboration measurement of B(→ 0 0 ␥)ϭ(7.2Ϯ2.5)ϫ10 Ϫ5 ͓2͔, but it has a higher accuracy.On the theoretical side, → 0 0 ␥ decay was first studied by Singer ͓3͔, who postulated that this transition proceeds through the →() 0 → 0 0 ␥ mechanism involving a -meson intermediate state. The contribution of intermediate vector meson dominance ͑VMD͒ to the vector meson decays into two pseudoscalars and a single photon, V → PPЈ␥, was also considered by Bramon et al. ͓4͔ using standard Lagrangians obeying SU͑3͒ symmetry, and in particular for the branching ratio of the decay → 0 0 ␥ they obtained the result B(→ 0 0 ␥)ϭ2.8ϫ10 Ϫ5 . The V → PPЈ␥ decays have also been considered within the framework of chiral effective Lagrangians using chiral perturbation theory. Bramon et al. ͓5͔ studied various such decays using this approach and they noted that if chiral perturbation theory Lagrangians are used there is no tree-level contribution to the amplitudes for the decay processes V→ PPЈ␥, and moreover the one-loop contributions are finite and to this order no counterterms are required. They considered both and KK intermediate loops.In the good isospin limit -loop contributions to → 0 0 ␥ amplitude vanish, and the contribution of the K loops is two orders of magnitude smaller than the contribution of the VMD amplitude. Therefore, the VMD amplitude essentially accounts for the decay rate of the → 0 0 ␥ decay. Guetta and Singer ͓6͔ recently updated the theoretical value for the branching ratio B( → 0 0 ␥) of the decay → 0 0 ␥ as B(→ 0 0 ␥) ϭ(4.1Ϯ1.1)ϫ10 Ϫ5 . In their calculation they noted that when the Born amplitude for the VMD mechanism is used the decay rate → 0 0 ␥ is proportional to the coupling constants g 2 and g ␥ 2 , and they assumed that the decay →3 proceeds with the same mechanism as → 0 0 ␥, that is, as →()→ ͓7͔. They used the experimental inputs for the decay rates ⌫(→3), ⌫( 0 → 0 ␥), and ⌫(→), and furthermore they employed a momentum dependent width for the meson. If a constant -meson width is used, then the value B(→ 0 0 ␥)ϭ(3.6Ϯ0.9) ϫ10 Ϫ5 is obtained for the branching r...

We analyze the constraint structure of the interaction of vector mesons with baryons using the classical Dirac constraint analysis. We show that the standard interaction in terms of two independent SU(3) structures is consistent at the classical level. We then require the self-consistency condition of the interacting system in terms of perturbative renormalizability to obtain relations for the renormalized coupling constants at the one-loop level. As a result we find a universal interaction with one coupling constant which is the same as in the massive Yang-Mills Lagrangian of the vector-meson sector.