The decay $\rho^{0}\to \pi^{0}\pi^{0}\gamma$ and the role of $\sigma$-meson

The new data on $\rho,\omega,\phi$ radiative decays into $\pi^0\gamma,\eta\gamma,\eta'\gamma$ from SND experiment at VEPP-2M $e^+e^-$ collider are presented.

We study the rho^0 and phi decays into pi^+ pi^- gamma, pi^0 pi^0 gamma and phi into pi^0 eta gamma using a chiral unitary approach to deal with the final state interaction of the M M system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the rho^0 --> pi^+ pi^- gamma decay. In the case of phi decay the contribution to pi^+ pi^- gamma and pi^0 pi^0 gamma decay proceeds via kaonic loops and gives a distribution of pi pi in...

We evaluate radiative decays of $\rho$ and $\omega$ going to two neutral mesons, $\pi^{0} \pi^{0}$ and $\pi^{0} \eta$. We use the sequential vector decay mechanisms in addition to chiral loops and $\rho$-$\omega$ mixing. The chiral loops are obtained using elements of $U\chi PT$ successfully applied in the study of meson-meson interactions up to 1.2 GeV. The chiral loops are found very important in the case of the $\rho \to \pi^{0} \pi^{0} \gamma$ decay and small in the other...

We describe the interference between amplitudes $e^ + e^-\to\rho\to\gamma\pi^+\pi^-$ and $e^ + e^-\to\phi\to\gamma (f_0 + \sigma) \to\gamma\pi^ + \pi^-$, with regard to the phase of the elastic $\pi\pi$ scattering background and mixing of the $f_0$ and $\sigma$ mesons. It is shown that the Fermi-Watson theorem for the final state interaction in the reaction $e^ + e^-\to\rho\to\gamma\pi^ + \pi^-$ is not valid in the case of soft photons, $\omega < 100$ MeV, in the $\phi$ meson...

It is discussed the problem of the $\rho^\pm-\rho^0$ mass splitting. It is suggested to use the $\phi\to\rho\pi\to 3\pi$ decay to measure the $\rho^{\pm}-\rho^0$ mass splitting.

Influence of the isospin-violating (\rho^0, \omega)-mixing is discussed for any pair of decays of \rho^0, \omega into the same final state. It is demonstrated, in analogy to the CP-violation in neutral kaon decays, that isospin violation can manifest itself in various forms: direct violation in amplitudes and/or violation due to mixing. In addition to the known decays (\rho^0, \omega)\to\pi^+\pi^- and (\rho^0, \omega)\to\pi^0\gamma, the pair of decays to e^+e^- and the whole ...

A theoretical analysis of the $(\pi^-,\gamma\gamma)$ reaction in nuclei is made in order to find the viability of this reaction to test modifications of the $\sigma$ meson mass in nuclear matter. The $\pi\pi$ correlation in the scalar-isoscalar channel in nuclear matter could, in principle, manifest itself in this reaction since it plays an important role in the $\pi\pi\to\gamma\gamma$ mechanism. But we conclude that this effect is hardly visible in this reaction due to the s...

We study the effect of scalar-isoscalar $f_{0}(980)$ meson in the mechanism of the radiative $\phi\to \pi^{+}\pi^{-}\gamma$ decay. A phenomenological approach is used to study this decay by considering the contributions of $\sigma$-meson, $\rho$-meson and $f_{0}(980)$-meson. The interference effects between different contributions are analyzed and the branching ratio for this decay is calculated. We observe that $f_0$ meson contribution is much larger than the contributions o...

In this paper, radiative decays $\rho^0 \to \pi^+\pi^-\gamma, \pi^0\pi^0\gamma$ ,$\phi \to K^+K^-\gamma, K^0 \bar{K^0}\gamma$ are studied systematically in the U(3)$_L\timesU(3)_R$ chiral theory of mesons. The theoretical differential spectrum with respect to photon energy and branch ratio for $\rho^0 \to \pi^+\pi^-\gamma$ agree well with the experimental data. Differential spectrums and branch ratios for $\rho^0 \to \pi^0\pi^0\gamma, \phi \to K^+ K^-\gamma,\phi \to K^0\bar{K...

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 agreeme...