Nonperturbative corrections to the quark self-energy

Nonperturbative self-energy of a bound quark is computed gauge-invariantly in the framework of background perturbation theory. The resulting Deltam(q) (2) is negative and is a universal function of string tension and current q uark mass. The shift of hadron mass squared, M-2, due to Deltam(q)(2) is ne gative, large for light quarks, and solves the long-standing problem of Reg ge intercepts in relativistic quark models. (C) 2001 Published by Elsevier Science B.V.