We give a notion of the potentially good reduction locus of a Shimura variety. It
consists of the points which should be related with motives having potentially good
reductions in some sense. We show the existence of such locus for a Shimura variety
of preabelian type. Further, we construct a partition of the adic space associated to a
Shimura variety of preabelian type, which is expected to describe degenerations of
motives. Using this partition, we prove that the cohomology of the potentially good
reduction locus is isomorphic to the cohomology of a Shimura variety up to
nonsupercuspidal parts.
Keywords
Shimura variety, good reduction, adic space, nearby cycle