EXOTIC SYMMETRIC SPACE OVER A FINITE FIELD,II

This paper is the second of the papers of the same title. In this paper, we prove a conjecture of Achar–Henderson, which asserts that the Poincaré polynomials of the intersection cohomology complex associated to the closure of Sp_2n -orbits in the Kato's exotic nilpotent cone coincide with the modified Kostka polynomials indexed by double partitions, introduced by the first author. Actually, this conjecture was recently proved by Kato by a different method. Our approach is based on the theory of character sheaves on the exotic symmetric space.