2A-orbifold construction and the baby-monster vertex operator superalgebra

In this article we give a new proof of the determination of the full automorphism group of the baby-monster vertex operator superalgebra based on a theory of simple current extensions. As a corollary, we also prove that the Z2-orbifold construction with respect to a 2A-involution of the Monster applied to the moonshine vertex operator algebra V yields V itself again.