Stochastic Matching with Polynomial Degree

Abstract

We study the stochastic matching problem, where a graph $G$ is known in advance, but each edge survives independently with probability $p$. The goal is to select a subgraph $H$ of small maximum degree before seeing the surviving edges, while preserving a $(1-ε)$ fraction of the expected maximum matching size. This problem has received significant attention due to its numerous applications in kidney exchange, labor markets, and online dating. In this paper, we show there is always a subgraph $H \subseteq G$ achieving a $(1-ε)$-approximation while having a maximum degree of at most $O\left(\frac{\log(1/ε)}{ε^4} \cdot \frac{1}{p}\right).$ This resolves a major conjecture of the literature, first stated by [BDH, STOC'20], that $poly(\frac{1}{εp})$ degrees suffice. The best previous bound was $(1/p)^{\exp((1/ε)\log(1/ε))}$ by [ABGR, STOC'25]. The key to this result is a lemma of independent interest that any distribution over the matchings of a stochastic graph can be transformed to another distribution which matches each vertex with exactly the same probability, but exhibits extremely low total pairwise correlation.