Spectral Threshold for Extremal Cyclic Edge-Connectivity.

The universal cyclic edge-connectivity of a graph G is the least k such that there exists a set of k edges whose removal disconnects G into components where every component contains a cycle. We show that for graphs of minimum degree at least 3 and girth g at least 4, the universal cyclic edge-connectivity is bounded above by (Δ - 2) g where Δ is the maximum degree. We then prove that if the second eigenvalue of the adjacency matrix of a d-regular graph of girth g ≥ 4 is sufficiently small, then the universal cyclic edge-connectivity is (d - 2) g , providing a spectral condition for when this upper bound on universal cyclic edge-connectivity is tight. [ABSTRACT FROM AUTHOR]