  Gribov's theory of light quark confinement implies the existence of two kinds
of scalar bound states. The phase diagram of the three-flavor QCD is mapped out
in the (m_pi-m_K)-plane with help of the SU_L(3)xSU_R(3) linear sigma model
supplemented with the assumption that the masses of the so-called superbound
scalars do not change under the variation of the pion and kaon mass. The phase
boundary along the m_pi=m_K line is found in the interval 15 MeV<m_crit<25 MeV,
irrespective which f_0-sigma linear combination is identified with the pure
superbound state.
