Wildly ramified unitary local models for special parahorics. The odd dimensional case

Abstract

We construct local models for wildly ramified unitary similitude groups of odd dimension $n\ge 3$ with special parahoric level structure and signature $(n-1,1)$. We first give a lattice-theoretic description for parahoric subgroups using Bruhat-Tits theory in residue characteristic two, and apply them to define local models following the lead of Rapoport-Zink and Pappas-Rapoport. In our case, there are two conjugacy classes of special parahoric subgroups. We show that the local models are smooth for the one class and normal, Cohen-Macaulay for the other class. We also prove that they represent the v-sheaf local models of Scholze-Weinstein. Under some additional assumptions, we obtain an explicit moduli interpretation of the local models.

Final version, to appear in Algebra & Number Theory