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 Δm2q is negative and is a universal function of string tension and current quark mass. The shift of hadron mass squared, M2, due to Δm2q is negative, large for light quarks, and solves the long-standing problem of Regge intercepts in relativistic quark models.