Аннотация:For heavy $q\overline{q}$ bound states in quantum chromodynamics, spin-dependent forces are obtained in a manifestly gauge-invariant formalism. Classical spin-orbit and Thomas precession terms are expressed in general in terms of the static energy, and assuming that the confinement mechanism is electric determines uniquely the spin-dependent forces in terms of the nonrelativistic potential. The Coulomb plus linear potential model gives $P$-state splittings correct to better than 25% and a mass for the ${\ensuremath{\eta}}_{c}$ of 3.030\ifmmode\pm\else\textpm\fi{}0.020 GeV.
Ключевые слова:Quantum Chromodynamics and Particle Interactions, Physics of Superconductivity and Magnetism, Superconducting Materials and Applications
