Heterotic Parafermionic Superstring
  Superstrings have been postulated based on parafermionic partition functions which permit spacetime supersymmetry by generalized Jacobi identities. A comprehensive search finds new such identities. Quadrilateral anomaly cancellation gives constraints on allowed chiral fermions. Bosonic left-movers and $Z_4$ parafermionic right-movers combine in a new heterotic superstring, more constrained than the old one, yet equally applicable to physics. 
Paul H. Frampton and James T. Liu