ON GENERALIZED FRACTIONAL SUPERSTRING THEORY

We extend the work of Argyres and Tye (1991 Phys. Rev. Lett. 67 3339) on fractional superstrings established for su(k)(2)/u(1) to higher-dim ensional parafermionic cosets. We derive the generic formula for the c ritical spacetime dimensions and the corresponding critical central ch arges for the more general su(k)(N)/u(1)(N-1) coset N = 2,3,.... We al so show that only the cosets su(2)(2)/u(1) and su(3)(3)/u(1)(2) allow one to build critical (N, k)-string models. Other features are also di scussed.