History and new ideas for exotic particles
  Basic 1966 physics of Sakharov, Zeldovich and Nambu updated by QCD with constituent-quark quasiparticles having effective masses fits all masses and magnetic moments of ground state meson and baryons having no more than one strange or heavy quark Flavor antisymmetry explains absence of low-lying exotics and suggests diquark-triquark model and two-state model for $\Theta^+$ pentaquark. Variational approach gives mass bounds for other pentaquarks. 
Harry J. Lipkin