The 't Hooft determinant resolution of the eta' puzzle
Abstract
The six-quark instanton induced 't Hooft interaction, which breaks the unwanted UA(1) symmetry of QCD, is also a sourse of semi-classical corrections to the low energy effective action. It is argued that there emerges a dimensionless expansion parameter that introduces a new mass scale, LambdaE2=6 GeV2, in the 0-, 0+ channels. This scale plays a similar role as the large critical mass M2crit > 4.2-6.6 GeV2 discovered in the framework of QCD sum rules in the 0-, 0+ gluonic channels. In particular, it allows to resolve the eta' puzzle. To extract LambdaE we calculate the masses of the lightest pseudoscalar meson nonet by using the Nambu --Jona-Lasinio (NJL) type UL(3)X UR(3) chiral symmetric Lagrangian together with the 't Hooft determinant. The mechanism which leads to the large value of LambdaE is scrutinized.
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