An improved threshold for the number of distinct intersections of intersecting families

TL;DR

This paper improves bounds on the number of distinct intersections in t-intersecting families of subsets, extending previous results to larger n and refining thresholds for intersecting families.

Contribution

It establishes new upper bounds for the size of the set of distinct intersections in t-intersecting families, generalizing prior work and improving the threshold from quadratic to near-linear in k.

Findings

Established upper bounds for the size of intersection sets in t-intersecting families.

Extended the validity of bounds to larger n beyond previous thresholds.

Improved the threshold from quadratic to near-linear in k for intersecting families.

Abstract

A family $\mathcal{F}$ of subsets of $\{1,2,\ldots,n\}$ is called a $t$-intersecting family if $|F\cap G| \geq t$ for any two members $F, G \in \mathcal{F}$ and for some positive integer $t$. If $t=1$, then we call the family $\mathcal{F}$ to be intersecting. Define the set $\mathcal{I}(\mathcal{F}) = \{F\cap G: F, G \in \mathcal{F} \text{ and } F \neq G\}$ to be the collection of all distinct intersections of $\mathcal{F}$. Frankl et al. proved an upper bound for the size of $\mathcal{I}(\mathcal{F})$ of intersecting families $\mathcal{F}$ of $k$-subsets of $\{1,2,\ldots,n\}$. Their theorem holds for integers $n \geq 50 k^2$. In this article, we prove an upper bound for the size of $\mathcal{I}(\mathcal{F})$ of $t$-intersecting families $\mathcal{F}$, provided that $n$ exceeds a certain number $f(k,t)$. Along the way we also improve the threshold $k^2$ to $k^{3/2+o(1)}$ for the intersecting families.