Speaker
Prof.
Nikolay Achasov
(Sobolev Institute for Mathematics)
Description
The light scalar meson problem which has arisen 50 years ago from the linear sigma model ( LSM), became central in the nonperturbative QCD since LSM could be its low energy realization. The scalar channels in the region up to 1 GeV is a stumbling block of QCD. The point is that not only perturbation theory fails here, but sum rules as well in view of the fact that isolated resonances are absent in this region.
Attention is paid to the production mechanisms of light scalars that reveal their nature.
It is revealed the chiral shielding of the \sigma(600) meson and shown that the \sigma field is described by its four-quark component in the \sigma resonance energy (virtuality) region.
The \pi\pi scattering amplitude with regular analytical properties in the s complex plane is constructed taking into account the chiral shielding of the \sigma (600) meson and its mixing with the f_0(980) meson.The data agrees with the four-quark nature of the \sigma (600) and f_0(980) mesons. The amplitude in the range -5 m_\pi^2 < s < 0.64 GeV^2 also agrees with results, obtained on the base of the chiral expansion, dispersion relations, and the Roy equations.
It is shown that the kaon loop mechanism of the \phi radiative decays, ratified by experiment, is the four-quark transition and points to the four-quark nature of light scalars.
It is shown also that the light scalars are produced in the two photon collisions via four-quark transitions in contrast to the classic P wave tensor q\bar q mesons that are produced via two-quark transitions \gamma\gamma\to q\bar q.
A programme of further investigations is laid down.
Primary author
Prof.
Nikolay Achasov
(Sobolev Institute for Mathematics)
