  The surprising thing is that the light scalar meson problem, arising 50 years
ago from the linear sigma model (LSM) with spontaneously broken chiral
symmetry, has become central in the nonperturbative quantum chromodynamics
(QCD), because it has been made clear that LSM could be the low energy
realization of QCD. First, we review briefly signs of four-quark nature of
light scalars. Then we show 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->q\bar q. Thus we get new evidence of the four-quark nature of the
lower scalar states.
