Dv. Antonov et D. Ebert, TOPOLOGICAL TERM IN THE STRING REPRESENTATION OF THE WILSON LOOP IN THE DILUTE INSTANTON GAS APPROXIMATION - ART. NO. 067901, Physical review. D. Particles and fields, 5806(6), 1998, pp. 7901
A topological term related to the number of self-intersections of the
string world sheet is shown to emerge in the string representation of
the Wilson loop in the dilute instanton gas. The coupling constant of
this term turns out to be proportional to the topological charge of th
e instanton gas under consideration. [S0556-2821(98)08216-2].