Density Frankl-Rödl on the Sphere

Abstract

We establish a density variant of the Frankl-Rödl theorem on the sphere ${\mathbb{S}}^{n-1}$, which concerns avoiding pairs of vectors with a specific distance, or equivalently, a prescribed inner product. In particular, we establish lower bounds on the probability that a randomly chosen pair of such vectors lies entirely within a measurable subset $A\subseteq {\mathbb{S}}^{n-1}$ of sufficiently large measure. Additionally, we prove a density version of spherical avoidance problems, which generalize from pairwise avoidance to broader configurations with prescribed pairwise inner products. Our framework encompasses a class of configurations we call inductive configurations, which include simplices with any prescribed inner product $-1<r<1$. As a consequence of our density statement, we show that all inductive configurations are sphere Ramsey.