Tensor product weight modules over the Virasoro algebra

TL;DR

This paper establishes necessary and sufficient conditions for the simplicity of tensor products of highest weight and intermediate series modules over the Virasoro algebra, advancing understanding of their irreducibility and isomorphism classes.

Contribution

It provides a complete characterization of when these tensor products are simple, introducing a shifting technique and utilizing Feigin-Fuchs' Theorem.

Findings

Derived conditions for tensor product irreducibility.

Identified when two tensor products are isomorphic.

Connected non-simple tensor products to other simple Virasoro modules.

Abstract

The tensor product of highest weight modules with intermediate series modules over the Virasoro algebra was discussed by Zhang [Z] in 1997. Since then the irreducibility problem for the tensor products has been open. In this paper, we determine the necessary and sufficient conditions for these tensor products to be simple. From non-simple tensor products, we can get other interesting simple Virasoro modules. We also obtain that any two such tensor products are isomorphic if and only if the corresponding highest weight modules and intermediate series modules are isomorphic respectively. Our method is to develop a "shifting technique" and to widely use Feigin-Fuchs' Theorem on singular vectors of Verma modules over the Virasoro algebra.