Journal Article
Binary quartic forms having bounded invariants, and the boundedness of the average rank of elliptic curves
Manjul Bhargava and Arul Shankar
Annals of Mathematics
SECOND SERIES, Vol. 181, No. 1 (January, 2015), pp. 191-242
Published
by: Mathematics Department, Princeton University
https://www.jstor.org/stable/24522952
Page Count: 52
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Topics: Discriminants, Cubic functions, Solubility, Mathematical theorems, Uniformity, Curves, Multisets, Mathematical rings, Polynomials, Equivalence relation
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Abstract
We prove a theorem giving the asymptotic number of binary quartic forms having bounded invariants; this extends, to the quartic case, the classical results of Gauss and Davenport in the quadratic and cubic cases, respectively. Our techniques are quite general and may be applied to counting integral orbits in other representations of algebraic groups. We use these counting results to prove that the average rank of elliptic curves over ℚ, when ordered by their heights, is bounded. In particular, we show that when elliptic curves are ordered by height, the mean size of the 2-Selmer group is 3. This implies that the limsup of the average rank of elliptic curves is at most 1.5.
Annals of Mathematics
© 2015 Annals of Mathematics
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