Hecke orbits as Shimura varieties in positive characteristic
Hecke orbits as Shimura varieties in positive characteristic
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赫克轨道作为志村品种的积极特征
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发表时间:
2006
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通讯作者:
C. Chai
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作者:
C. Chai
Let p be a prime number, and let M be a modular variety of PEL type over Fp
which classifies abelian varieties in characteristic p with extra symmetries of a fixed PEL type.
Consider the p-divisible group with extra symmetries consisting of all p-power torsions of
the universal abelian scheme over M. The locus in M corresponding to a fixed isomorphism
type of a p-divisible group with extra symmetry is called a leaf by F. Oort. Each leaf is a
smooth locally closed subvariety of the modular varietyM which is stable under all prime-to-p
Hecke correspondences on M. Oort conjectured that every Hecke orbit is dense in the leaf
containing it. Tools fashioned for this conjecture include (a) rigidity, (b) global monodromy,
and (c) canonical coordinates. The theory of canonical coordinates generalizes the classical
Serre�Tate coordinates; it asserts that locally at the level of jet-spaces, every leaf is built up
from p-divisible formal groups through a finite family of fibrations in a canonical way. The
Hecke orbit conjecture is affirmed when M is a Siegel modular variety classifying principally
polarized abelian varieties of a fixed dimension, and also when M is a Hilbert modular variety
classifying abelian varieties with real multiplications. The proof of the Siegel case, joint with
F. Oort, uses the irreducibility of non-supersingular leaves in Hilbert modular varieties due to
C.-F.Yu. That proof relies heavily on a special property of Siegel modular varieties: The set of
Fp-rational points of a Siegel modular variety Ag,n is filled up by Fp-rational points of Hilbert
modular varieties contained in Ag,n. Possible directions for further progress include Tate-linear
subvarieties and p-adic monodromy. The title of this article suggests that each leaf deserves to
be viewed as a Shimura variety in characteristic p in its own right.