On Orthogonal Local Models of Hodge Type

Abstract

Abstract We study local models that describe the singularities of Shimura varieties of non-PEL type for orthogonal groups at primes where the level subgroup is given by the stabilizer of a single lattice. In particular, we use the Pappas–Zhu construction and we give explicit equations that describe an open subset around the “worst” point of orthogonal local models given by a single lattice. These equations display the affine chart of the local model as a hypersurface in a determinantal scheme. Using this, we prove that the special fiber of the local model is reduced and Cohen–Macaulay.