$U_A(1)$ Symmetry Breaking and the Scalar Sector of QCD
  It is shown that most of the unusual properties of the lowest lying scalar (and pseudoscalar) mesons can be understood, at the qualitative and quantitative level, on the basis of the breakdown of the $U_A(1)$ symmetry coupled to the vacuum expectation values of scalars by the spontaneous breaking of chiral symmetry. 
Mauro Napsuciale and Simon Rodriguez