Possible retardation effects of quark confinement on the meson spectrum
  The reduced Bethe-Salpeter equation with scalar confinement and vector gluon exchange is applied to quark-antiquark bound states. The so called intrinsic flaw of Salpeter equation with static scalar confinement is investigated. The notorious problem of narrow level spacings is found to be remedied by taking into consideration the retardation effect of scalar confinement. Good fit for the mass spectrum of both heavy and light quarkomium states is then obtained. 
Cong-feng Qiao, Han-Wen Huang, Kuang-Ta Chao (Peking University)