We prove that bounded-degree expanders with non-negative Ollivier-Ricci curvature do not exist, thereby solving a long-standing open problem suggested by Naor and Milman and publicized by Ollivier (2010). In fact, this remains true even if we allow for a vanishing proportion of large degrees, large eigenvalues, and negatively-curved edges. To prove this, we work directly at the level of Benjamini-Schramm limits, and exploit the entropic characterization of the Liouville property on stationary random graphs to show that non-negative curvature and spectral expansion are incompatible "at infinity". We then transfer this result to finite graphs via local weak convergence and a relative compactness argument. We believe that this "local weak limit" approach to mixing properties of Markov chains will have many other applications.
翻译:我们证明没有带有非阴性奥利维埃-里基曲曲线的封闭度扩张器,从而解决了纳奥和米尔曼提出的、奥利维埃(2010年)公布的长期未决问题。事实上,即使我们允许大度、大电子值和负曲线边缘的消失比例,这也仍然是真实的。为了证明这一点,我们直接在Benjani-Schramm极限层面工作,利用固定随机图对利奥维尔财产进行昆虫特征描述,以显示非阴性曲线和光谱扩张不相容的“无限性 ” 。 我们随后通过本地薄弱的趋同和相对紧凑性的论点将这一结果转移到有限的图表中。 我们相信,这种将马尔科夫链的特性混杂在一起的“局部弱度限制”方法将有许多其他应用。