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Random Dieudonné modules, random $p$-divisible groups, and random curves over finite fields

Published online by Cambridge University Press:  13 February 2013

Bryden Cais
Affiliation:
Department of Mathematics, The University of Arizona, 617 N. Santa Rita Ave., P.O. Box 210089, Tucson, AZ 85721-0089, USA (cais@math.arizona.edu)
Jordan S. Ellenberg
Affiliation:
Department of Mathematics, University of Wisconsin-Madison, 480 Lincoln Drive, Madison, WI 53706, USA (ellenber@math.wisc.edu)
David Zureick-Brown
Affiliation:
Dept. of Math and Computer Science, Emory University, 400 Dowman Dr., W401, Atlanta, GA 30322, USA (dzb@mathcs.emory.edu)

Abstract

We describe a probability distribution on isomorphism classes of principally quasi-polarized $p$-divisible groups over a finite field $k$ of characteristic $p$ which can reasonably be thought of as a ‘uniform distribution’, and we compute the distribution of various statistics ($p$-corank, $a$-number, etc.) of $p$-divisible groups drawn from this distribution. It is then natural to ask to what extent the $p$-divisible groups attached to a randomly chosen hyperelliptic curve (respectively, curve; respectively, abelian variety) over $k$ are uniformly distributed in this sense. This heuristic is analogous to conjectures of Cohen–Lenstra type for $\text{char~} k\not = p$, in which case the random $p$-divisible group is defined by a random matrix recording the action of Frobenius. Extensive numerical investigation reveals some cases of agreement with the heuristic and some interesting discrepancies. For example, plane curves over ${\mathbf{F} }_{3} $ appear substantially less likely to be ordinary than hyperelliptic curves over ${\mathbf{F} }_{3} $.

Type
Research Article
Copyright
©Cambridge University Press 2013 

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