Parafermionic quasi-particle basis and fermionic-type characters

A quasi-particle basis of states for highest-weight modules in Z(k) parafermionic conformal theories is displayed. It is formulated in terms of an effective exclusion principle constraining strings of k fundamental parafermionic modes. The states of a module are then built by a simple filling process, with no singular-vector subtractions. That results in fermionic-sum representations of the characters, which are exactly the Lepowsky-Primc expressions. We also stress that the underlying combinatorics-which is the one pertaining to the Andrews-Gordon identities-has a remarkably natural parafermionic interpretation. (C) 2002 Elsevier Science B.V. All rights reserved.