On the Structure of Framed Vertex Operator Algebras and Their Pointwise Frame Stabilizers

In this paper, we study the structure of a general framed vertex operator algebra (VOA). We show that the structure codes (C,D) of a framed VOA V satisfy certain duality conditions. As a consequence, we prove that every framed VOA is a simple current extension of the associated binary code VOA V _C . This result suggests the feasibility of classifying framed vertex operator algebras, at least if the central charge is small. In addition, the pointwise frame stabilizer of V is studied. We completely determine all automorphisms in the pointwise stabilizer, which are of order 1, 2 or 4. The 4A-twisted sector and the 4A-twisted orbifold theory of the famous moonshine VOA are also constructed explicitly. We verify that the top module of this twisted sector is of dimension 1 and of weight 3/4 and the VOA obtained by 4A-twisted orbifold construction of is isomorphic to itself. Dedicated to Professor Koichiro Harada on his 65th birthday Partially supported by NSC grant 94-2115-M-006-001 of Taiwan, R.O.C. Supported by JSPS Research Fellowships for Young Scientists.