Local heuristics and exact formulas for counting elliptic curves over finite fields
Connections for Women: New Geometric Methods in Number Theory and Automorphic Forms August 14, 2014  August 15, 2014
Location: SLMath: Eisenbud Auditorium
14039
Consider the question: how likely is a random elliptic curve over the finite field F_p to have exactly N rational points, where N is a given integer in the appropriate range? In 2003, Gekeler gave an explicit answer based on a heuristic that was too strong to be literally true, thus the answer appeared somewhat mysterious. We provide an explanation for this formula by making an explicit and very natural connection with a formula of Langlands and Kottwitz which expresses the size of an isogeny class of principally polarized abelian varieties in terms of an adelic orbital integral. Then we discuss a possible extension of Gekeler's computations from elliptic curves to abelian varieties.
This is joint work with Jeff Achter.
14039
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