{ "id": "1310.1430", "version": "v2", "published": "2013-10-05T02:37:23.000Z", "updated": "2014-02-25T15:24:08.000Z", "title": "An asymptotically tight bound on the Q-index of graphs with forbidden cycles", "authors": [ "V. Nikiforov" ], "comment": "10 pages. Version 2 takes care of some mistakes in version 1", "categories": [ "math.CO" ], "abstract": "Let G be a graph of order n and let q(G) be that largest eigenvalue of the signless Laplacian of G. In this note it is shown that if k>1 and q(G)>=n+2k-2, then G contains cycles of length l whenever 2