The subconstituent algebra of a bipartite distance-regular graph; thin modules with endpoint two

Abstract

We consider a bipartite distance-regular graph $G$ with diameter at least 4 and valency at least 3. Fix a vertex of $G$ and let $T$ denote the corresponding subconstituent algebra. We give a detailed description of a certain type of irreducible $T$-module, said to be thin with endpoint 2.