Pseudoscalar Meson Radial Excitations
  Goldstone modes are the only pseudoscalar mesons to possess a nonzero leptonic decay constant in the chiral limit when chiral symmetry is dynamically broken. The decay constants of their radial excitations vanish. These features and aspects of their impact on the meson spectrum are illustrated using a manifestly covariant and symmetry preserving model of the kernels in the gap and Bethe-Salpeter equations. 
A.Hoell, A.Krassnigg and C.D.Roberts