English

Rational normal curves as no-$(d+2)$-on-$Q$-quadric sets

Combinatorics 2025-11-06 v1 Algebraic Geometry

Abstract

For every d2d\geq 2, we construct a subset D{1,2,,n}dD\subseteq \{1,2,\dots,n\}^d of size no(n)n-o(n) such that every affine hyperplane of Rd\mathbb{R}^d intersects DD in at most dd points, and every hypersphere of Rn\mathbb{R}^n intersects DD in at most d+1d+1 points. This construction is the largest one currently known, and strongly builds on ideas of Dong, Xu, and also of Thiele. More generally, we prove that the role of hyperspheres can be replaced by QQ-quadrics, i.e. by quadratic surfaces given by an equation whose degree two homogeneous part equals a fixed quadratic form QQ. We formulate analogous statements in affine spaces over (finite) fields. Essentially, every construction is given by a suitable rational normal curve in a dd-dimensional projective space.

Keywords

Cite

@article{arxiv.2511.03526,
  title  = {Rational normal curves as no-$(d+2)$-on-$Q$-quadric sets},
  author = {Dávid R. Szabó},
  journal= {arXiv preprint arXiv:2511.03526},
  year   = {2025}
}

Comments

First draft, comments welcome. 13 pages

R2 v1 2026-07-01T07:22:57.542Z