English

How often does a cubic hypersurface have a rational point?

Number Theory 2024-05-13 v1

Abstract

A cubic hypersurface in Pn\mathbb{P}^n defined over Q\mathbb{Q} is given by the vanishing locus of a cubic form ff in n+1n+1 variables. It is conjectured that when n4n \geq 4, such cubic hypersurfaces satisfy the Hasse principle. This is now known to hold on average due to recent work of Browning, Le Boudec, and Sawin. Using this result, we determine the proportion of cubic hypersurfaces in Pn\mathbb{P}^n, ordered by the height of ff, with a rational point for n4n \geq 4 explicitly as a product over primes pp of rational functions in pp. In particular, this proportion is equal to 1 for cubic hypersurfaces in Pn\mathbb{P}^n for n9n \geq 9; for 100%100\% of cubic hypersurfaces, this recovers a celebrated result of Heath-Brown that non-singular cubic forms in at least 10 variables have rational zeros. In the n=3n=3 case, we give a precise conjecture for the proportion of cubic surfaces in P3\mathbb{P}^3 with a rational point.

Keywords

Cite

@article{arxiv.2405.06584,
  title  = {How often does a cubic hypersurface have a rational point?},
  author = {Lea Beneish and Christopher Keyes},
  journal= {arXiv preprint arXiv:2405.06584},
  year   = {2024}
}

Comments

23 pages

R2 v1 2026-06-28T16:23:25.530Z