Spontaneous breakdown and the scalar nonet

In the context of the QCD quark model and on the basis of dynamical Bethe-Salpeter ladder graphs, we suggest that (i) the existence of the scalar $\overline{q}q$ hadron multiplet, like the pseudoscalar $\overline{q}q$ multiplet, is a direct consequence of dynamical spontaneous breakdown of chiral symmetry with a chiral-limiting nonstrange mass scale of $m_{\sigma \mathrm{NS}}^{\mathrm{CL}}=2\mathrm{}{m}_{\mathrm{dyn}}\approx 630$ MeV, (ii) the lifting of the nonstrange $\sigma -\delta$ degeneracy is expected from the $s$-wave quark-gluon annihilation diagram, and (iii) the observed $\delta -S^{*}$ mixing from the existence of the $p$-wave scalar quark-annihilation diagram. The resulting predicted $0^{++}$ $\overline{q}q$ nonet is then $\sigma \left(750\mathrm{} \mathrm{MeV}\right)$, $\kappa \mathrm{}\left(800\right)\mathrm{}$, $S^{*}\mathrm{}\left(980\right)\mathrm{}$, and $\delta \mathrm{}\left(985\right)\mathrm{}$, in agreement with data for the resonant masses, the mixing angle, and also decay widths except for the $\kappa \mathrm{}\left(800\right)\mathrm{}$.