A Solution of the Scalar Nonet Mass Puzzle

We present a short review dedicated to low-lying meson states. We present all meson 2 nonets, which consist from up, down and strange light quarks. We consider the scalar 3 nonet as a basic nonet. We work in the framework of the massless Nambu – Jona-Lasinio 4 UR(3) × UL(3) quark model. The collective meson states are described through quark- 5 antiquark pairs, whose condensates lead simultaneously to spontaneous breaking of the 6 chiral and the flavour symmetry. We present an explanation of the inverse mass hierarchy of 7 the low-lying nonet of the scalar mesons. The proposed explanation is based on symmetry 8 principles. It is shown that, due to the flavour symmetry breaking, two isodoublets of 9 K ∗ 0 (700) mesons play the role of Goldstone bosons. It is also proven that there exists a 10 solution with degenerate masses of the a0(980) and f0(980) mesons and a zero mass of 11 the f0(500) meson. Short description of the physical properties of other meson nonets is 12 provided. In particular a unique mass relations among the different nonets, which are 13 experimentally confirmed, are presented.