Refuting Perfect Matchings in Spectral Expanders is Hard

Abstract

This work studies the complexity of refuting the existence of a perfect matching in spectral expanders with an odd number of vertices, in the Polynomial Calculus (PC) and Sum of Squares (SoS) proof system. Austrin and Risse [SODA, 2021] showed that refuting perfect matchings in sparse $d$-regular \emph{random} graphs, in the above proof systems, with high probability requires proofs with degree $\hat{I}\text{c◯}(n/\log n)$. We extend their result by showing the same lower bound holds for \emph{all} $d$-regular graphs with a mild spectral gap.

Improved presentation, fixed minor issue in Proofs of Lemma 4.1 and 4.2. Accepted at SIAM Journal For Discrete Mathematics