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 "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 (resp. curve, resp. abelian variety) over k are uniformly distributed in
this sense.
Let A be the N\'eron model of an abelian variety A_K over the fraction field
K of a discrete valuation ring R. Due to work of Mazur-Messing, there is a
functorial way to prolong the universal extension of A_K by a vector group to a
smooth and separated group scheme over R, called the canonical extension of A.
In this paper, we study the canonical extension when A_K=J_K is the Jacobian of
a smooth proper and geometrically connected curve X_K over K.