Generalized parafermions of orthogonal type

Abstract

There is an embedding of affine vertex algebras Vk(gln)↪Vk(sln+1), and the coset Ck(n)=Com(Vk(gln),Vk(sln+1)) is a natural generalization of the parafermion algebra of sl2. It was called the algebra of generalized parafermions by the third author and was shown to arise as a one-parameter quotient of the universal two-parameter W∞-algebra of type W(2,3,…). In this paper, we consider an analogous structure of orthogonal type, namely Dk(n)=Com(Vk(so2n),Vk(so2n+1))Z2. We realize this algebra as a one-parameter quotient of the two-parameter even spin W∞-algebra of type W(2,4,…), and we classify all coincidences between its simple quotient Dk(n) and the algebras Wℓ(so2m+1) and Wℓ(so2m)Z2. As a corollary, we show that for the admissible levels k=−(2n−2)+12(2n+2m−1) for soˆ2n the simple affine algebra Lk(so2n) embeds in Lk(so2n+1), and the coset is strongly rational. As a consequence, the category of ordinary modules of Lk(so2n+1) at such a level is a braided fusion category.