Perfect matchings in hyperfinite graphings

Abstract

We characterize hyperfinite bipartite graphings that admit measurable perfect matchings. In particular, we prove that every regular hyperfinite bipartite graphing admits a measurable perfect matching if it is one-ended or the degree is odd. We give several applications of this result, answering various open questions in the field. For instance, we extend the Lyons--Nazarov theorem by characterizing bipartite Cayley graphs which admit a factor of iid perfect matching, answering the bipartite case of a well-known question of Lyons and Nazarov, popularized by Kechris and Marks. Moreover, we show how our results apply to measurable equidecompositions and, in particular, generalize the recent result of Grabowski, M\'ath\'e and Pikhurko on the measurable circle squaring. Our approach applies more generally to rounding measurable perfect fractional matchings.