THE QCD STRING WITH QUARKS - SPINLESS QUARKS

Starting from the QCD Lagrangian we derive the effective action for th e massive quark and antiquark at large distances, corresponding to the minimal-area law of the Wilson loop. The path-integral method is used to quantize the system, and the spectrum is obtained with asymptotica lly linear Regge trajectories. Two dynamical regimes distinguished by the string energy-momentum distribution are found: at large orbital ex citations (l much greater than 1) the system behaves as a string and y ields the Regge slope l/2pisigma, while at small l one obtains a poten tial-like regime for a relativistic or nonrelativistic system. The pro blem of relative time is clarified. It is shown that in the valence-qu ark approximation one can reduce the initial four-dimensional dynamics to the three-dimensional one. The limiting case of a pure string (wit hout quark kinetic terms) is studied, and the spectrum of the straight -line string is obtained.