Search for the scalar a_0 and f_0 mesons in the \phi radiative decays

The potentialities of the production of the $a_0$ and $f_0$ mesons in the $\phi$ radiative decays are considered based on a new two-channel analysis of the $\pi\pi$ scattering in a energy region near 1 GeV. We predict $BR(\phi\to\gamma f_0(980))\sim10^{-5}-10^{-4}$ that is a great value for the decay forbidden by the Okubo-Zweig-Iizuka rule. We discuss the four-quark, $K\bar K$-molecule and two-quark scenarios for the $a_0$ and $f_0$ mesons. It is presented arguments that the $e^+e^-$-colliders and especially the $\phi$ factories give the possibility to choose a single one out of them.Comment: Talk given at HADRON-9

Multiresonances of quasi-trapped modes in metasurfaces based on nanoparticles of transition metal dichalcogenides

The features of polarization control of multiple multiresonances for quasi-trapped modes excited by synchronization of bianisotropic dipole responses in MoS$_2$ disks with a hole are considered. Using the numerical calculations with analytical multipole analysis, we showed that the presence of a strong optical anisotropy of MoS$_2$ nanoparticles provides an additional degree of freedom and allows to observe several resonances of electric and magnetic dipoles at once in a narrow spectral range. Based on the simulation results, we obtained the frequency dependences for the dipole polarizabilities of the MoS$_2$ disk with a hole, which allow one to distinguish the contributions of the nonlocal and bianisotropic dipole responses and possessing several features in the near infrared range. Using the polarizability spectra of single nanoparticles and applying the tuning strategy, the design of the MoS$_2$ metasurface supporting three resonances of quasi-trapped modes at once in a narrow spectral range was developed. One of these resonances corresponds to the telecom wavelength of 1550 nm. The spectrum of light reflection for MoS$_2$ metasurface is characterized by three narrowband dips corresponding to the wavelengths of the quasi-trapped modes. It was shown that a change in the polarization of a wave normally incident on the metasurface to orthogonal one leads to a change in the type of bianisotropic response excited in each MoS$_2$ disk and to the excitation of three other features in the reflection spectra of the metasurface at wavelengths close to the initial values.Comment: 8 pages, 5 figure