Unified covariant treatment of hyperfine splitting for heavy and light   mesons
  This paper aims at proving the fundamental role of a relativistic formulation for quarkonia models.   We present a completely covariant description of a two-quark system interacting by the Cornell potential with a Breit term describing the hyperfine splitting. Using an appropriate procedure to calculate the Breit correction, we find heavy meson masses in excellent agreement with experimental data. Moreover, also when applied to light quarks and even taking average values of the running coupling constant, we prove that covariance properties and hyperfine splitting are sufficient to explain the light mesons spectrum and to give a very good agreement with the data. 
R. Giachetti, E. Sorace
hep-ph