Irreducibility of Local Models

In this paper, we consider the geometric special fibers of local models of Shimura varieties and of moduli of $\bG$-Shtukas with parahoric level structure. We investigate two problems with respect to the irreducibility of local models. First, we classify the cases where the local models are irreducible. Next, we show that the fibers of the level-changing map between the geometric special fiber of local models with different parahoric levels are always isomorphic to single (i.e., irreducible) Schubert varieties in the partial flag variety.