GHOST SYSTEMS - A VERTEX ALGEBRA POINT-OF-VIEW

Fermionic and bosonic ghost systems are defined each in terms of a sin gle vertex algebra which admits a one-parameter family of conformal st ructures. The observation that these structures are related to each ot her provides a simple way to obtain character formulae for a general t wisted module of a ghost system. The U(1) symmetry and its subgroups t hat underlie the twisted modules also define an infinite set of invari ant vertex subalgebras, Their structure is studied in detail from a W algebra point of view with particular emphasis on ZN-invariant subalge bras of the fermionic ghost system, (C) 1998 Elsevier Science B.V.