Sparse graphs with bounded induced cycle packing number have logarithmic treewidth

A graph is $O_k$-free if it does not contain $k$ pairwise vertex-disjoint and non-adjacent cycles. We prove that "sparse" (here, not containing large complete bipartite graphs as subgraphs) $O_k$-free graphs have treewidth (even, feedback vertex set number) at most logarithmic in the number of vertices, which is sharp already for $k=2$. As a consequence, most of the central NP-complete problems (such as Maximum Independent Set, Minimum Vertex Cover, Minimum Dominating Set, Minimum Coloring) can be solved in polynomial time in these graphs, and in particular deciding the $O_k$-freeness of sparse graphs is polytime.