Explanation of the Mass Pattern of the Low-Lying Scalar Nonet

The aim of this work is to propose an explanation of the inverse mass hierarchy of the low-lying nonet of the scalar mesons in the framework of the massless Nambu–Jona-Lasinio UR(3)×UL(3) quark model. The proposed explanation is based on symmetry principles. The collective meson states are described via quark–antiquark pairs, whose condensates lead simultaneously to spontaneous breaking of chiral and flavour symmetry. It is shown that, due to flavour symmetry breaking, two iso-doublets of K0*(700) mesons play the role of Goldstone bosons. It is also proven that there exists a solution with degenerate masses of the a0(980) and f0(980) mesons and a zero mass of the f0(500) meson.