0 v 1 2 8 Ju l 1 99 7 Potential regime for heavy quarks dynamics and Lorentz nature of confinement

Propagation of the heavy quark in the field of a static antiquark source is studied in the framework of effective Dirac equation. The model of QCD vacuum is described by bilocal gluonic correlators. In the heavy quark limit the effective interaction is reduced to the potential one with 5/6 Lorentz scalar and 1/6 Lorentz vector linear confinement, while spin–orbit term is in agreement with Eichten–Feinberg– Gromes results. New spin–independent corrections to the leading confining regime are identified, which arise due to the nonlocality of the interaction in time direction and quark Zitterbewegung. A lot of evidence exists that the non-abelian nature of Yang-Mills QCD leads to the confinement of colour charges. Apart from purely theoretical considerations, the main bulk of data on confinement comes from the lattice QCD simulations and from the phe-nomenology of hadronic spectra. The lattice calculations firmly establish the linear rising force between two static colour sources, while the hadronic masses are most successfully described with the effective q ¯ q potential which is the sum of linear and Coulomb forces. Complementary to these facts is the idea that QCD at large distances is a string theory , and linear potential between heavy constituents is a manifestation of the string–type dynamics. In general, the dynamics governed by QCD should be nonlocal; nevertheless, it is natural to assume that in the heavy quark limit it is reduced to the nonrelativistic local potential acting between quark and antiquark which is supplied by subleading O(1/m 2) corrections. Among these corrections an important role is played by spin-dependent forces which define the spin splittings of heavy quarkonia and serve as a testing ground for various theoretical approaches.