On integral forms for vertex algebras associated with affine Lie algebras and lattices

We revisit the construction of integral forms for vertex (operator) algebras V-L based on even lattices L using generators instead of bases, and we construct integral forms, for V-L-modules. We construct integral forms for vertex (operator) algebras based on highest-weight modules for affine Lie algebras and we exhibit natural generating sets. For vertex operator algebras in general, we give conditions showing when an integral form contains the standard conformal vector generating the Virasoro algebra. Finally, we study integral forms in contragredients of modules for vertex algebras. (C) 2014 Elsevier B.V. All rights reserved.