Symmetric noncrossing partitions of an annulus with double points

Abstract

For affine Coxeter groups of affine types $\tilde D$ and $\tilde B$, we model the interval $[1,c]_T$ in the absolute order by symmetric noncrossing partitions of an annulus with one or two double points. In type $\tilde B$ (and \emph{almost} in type $\tilde D$), the diagrams also model the larger lattice defined by McCammond and Sulway.