English

Bounded fractional intersecting families are linear in size

Combinatorics 2025-09-17 v2

Abstract

Using the sunflower method, we show that if θ(0,1)Q\theta \in (0,1) \cap \mathbb{Q} and F\mathcal{F} is a O(n1/3)O(n^{1/3})-bounded θ\theta-intersecting family over [n][n], then F=O(n)\lvert \mathcal{F} \rvert = O(n), and that if F\mathcal{F} is o(n1/3)o(n^{1/3})-bounded, then F(32+o(1))n\lvert \mathcal{F} \rvert \leq (\frac{3}{2} + o(1))n. This partially solves a conjecture of Balachandran, Mathew and Mishra that any θ\theta-intersecting family over [n][n] has size at most linear in nn, in the regime where we have no very large sets.

Keywords

Cite

@article{arxiv.2402.14981,
  title  = {Bounded fractional intersecting families are linear in size},
  author = {Niranjan Balachandran and Shagnik Das and Brahadeesh Sankarnarayanan},
  journal= {arXiv preprint arXiv:2402.14981},
  year   = {2025}
}

Comments

9 pages, 0 figures; added characterization of extremal families to second theorem; updated references