We study the radiative 0 → ϩ Ϫ ␥ and 0 → 0 0 ␥ decays and we calculate their branching ratios using a phenomenological approach by adding to the amplitude calculated within the framework of chiral perturbation theory and vector meson dominance the amplitude of -meson intermediate state. Our results for the branching ratios are in good agreement with the experimental values.The radiative decays of neutral vector mesons into a single photon and a pair of neutral pseudoscalar mesons have been a subject of continuous interest. The studies of such decays may serve as tests for the theoretical ideas about the nature of the intermediate states and the interesting mechanisms of these decays, and they may thus provide information about the complicated dynamics of meson physics in the low energy region.The very recent measurement of the branching ratio for the decay 0 → 0 0 ␥ by the SND Collaboration obtained the value BR( 0 → 0 0 ␥)ϭ(4.1 Ϫ0.9 ϩ1.0 Ϯ0.3)ϫ10 Ϫ5 ͓1͔, thus improving their previous preliminary report of BR( 0 → 0 0 ␥)ϭ(4.8 Ϫ1.8 ϩ3.4 Ϯ0.3)ϫ10 Ϫ5 ͓2͔. On the other hand, the branching ratio for the decay 0 → ϩ Ϫ ␥ was reported earlier by the Novosibirsk group as BR( 0 → ϩ Ϫ ␥) ϭ(9.9Ϯ1.6)ϫ10 Ϫ3 ͓3,4͔, and it was observed that the pion bremsstrahlung is the main mechanism for this decay with the structural radiation proceeding through the intermediate scalar resonance making less than one-order of magnitude smaller contribution to the branching ratio ͓3͔.The theoretical studies of radiative -meson decays was initiated by Singer ͓5͔ who calculated the amplitude for the decay 0 → ϩ Ϫ ␥ by considering only the bremsstrahlung mechanism, and he assumed that the decay 0 → 0 0 ␥ proceeds through an () intermediate state as 0 →() 0 →( 0 ␥) 0 . The vector meson dominance ͑VMD͒ calculation of Bramon et al. ͓6͔ with this intermediate state using standard Lagrangians obeying SU͑3͒ symmetry gave the value BR( 0 → 0 0 ␥)ϭ1.1ϫ10 Ϫ5 for the branching ratio. However, they also noted that final state interactions could lead to a larger value for the branching ratio BR( 0 → 0 0 ␥) through the mechanism 0 →( ϩ Ϫ )␥ →( 0 0 )␥. Bramon et al. ͓7͔ later considered the radiative vector meson decays within the framework of chiral effective Lagrangians enlarged to include on-shell vector mesons using chiral perturbation theory, and they calculated the branching ratios for various decays at the one-loop level, including both and KK intermediate loops. In this approach, the decay 0 → 0 0 ␥ proceeds mainly through the charged pion ( ϩ Ϫ ) loops, contribution of kaon-loops being three orders of magnitude smaller, resulting in the decay rate ⌫( 0 → 0 0 ␥) ϭ1.42 keV which is of the same order of magnitude as the VMD contribution. The interference between the pion-loop contribution and the VMD amplitude turns out to be constructive leading to BR( 0 → 0 0 ␥) VM Dϩ ϭ2.6ϫ10 Ϫ5 . However, this value is still substantially smaller than the latest experimental result quoted above.Since the experimental result for the branching ratio BR( 0 → 0 0 ␥) is alm...
Reanalyses of LEP data have shown preference to two light CP-even Higgs bosons. We discuss implications of such a Higgs boson spectrum for the minimal supersymmetric model extended by a standard model singlet chiral superfield and an additional Abelian gauge invariance [the U1 0 model]. We, in particular, determine parameter regions that lead to two light CP-even Higgs bosons while satisfying existing bounds on the mass and mixings of the extra vector boson. In these parameter regions, the pseudoscalar Higgs is found to be nearly degenerate in mass with either the lightest or next-to-lightest Higgs boson. Certain parameters of the U1 0 model such as the effective parameter are found to be significantly bounded by the LEP two light Higgs signal.
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.
We study the radiative decay ϕ → π0ηγ within the framework of a phenomenological approach in which the contributions of the ρ meson, chiral loop and a0 meson are considered. We analyse the interference effects between different contributions and utilizing the experimental branching ratio and invariant π0η mass spectrum for the ϕ → π0ηγ decay, we estimate the branching ratio of the ϕ → a0γ decay.
We study the anomalous magnetic moment of the muon in supersymmetric E 6 models and generic Uð1Þ 0 models to probe the model reactions and to find constraints on the large parameter space of these models. For future searches, by imposing the existing bounds coming from collider searches and theoretical considerations upon the Uð1Þ 0 model parameters, we examine the lightest Higgs boson mass m h and the mass of the additional Z boson m Z 2 in such singlet extensions of the MSSM. We observed that not only supersymmetric E 6 models but also generic Uð1Þ 0 models are sensitive to the imposition of the considered bounds. Indeed, without the muon anomaly constraints E 6 models and generic Uð1Þ 0 models can predict m h as large as $150 GeV and $180 GeV, respectively. However, in addition to the mentioned constraints when a 1 range for the anomalous magnetic moment of the muon is considered, we observe that generic Uð1Þ 0 models do not favor the mass of the lightest Higgs boson to be larger than 140 GeV; it should be smaller than 135 GeV in E 6 models.
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