On the structural growth of bipartite Ramsey numbers

TL;DR

This paper explores the growth behavior of bipartite Ramsey numbers, establishing bounds that depend on graph structure and density, with implications for cycles and bipartite graphs.

Contribution

It provides new asymptotic bounds for bipartite Ramsey numbers based on structural parameters and density, advancing understanding of their growth phenomena.

Findings

Lower bound: r(G,K_{n,n}) > C (n / log n)^{(q-1)/(p-2)}

Upper bound for multicolor bipartite Ramsey number of cycles: r_k(C_{2t};K_{n,n}) _{t,k} n^2 / log^2 n

Refined linear upper bound for bipartite Ramsey number of cycles and graphs:
br(C_{2t},G) rac{m}{2} + rac{29t\, ext{sqrt}(m)}{2}

Abstract

Bipartite Ramsey numbers is the smallest size of a complete bipartite graph $K_{N,N}$ such that every edge-coloring with a given number of colors inevitably yields a monochromatic copy of a prescribed bipartite graph. While exact values have been determined for certain specific graphs, the general asymptotic behavior of these numbers in terms of structural graph parameters remains poorly understood. In this paper, we investigate structure-dependent growth phenomena in bipartite Ramsey theory. For a fixed bipartite graph $G$ with $p$ vertices and $q$ edges, we first establish a lower bound of the form $\operatorname{br}(G,K_{n,n}) > C \bigl(\frac{n}{\log n}\bigr)^{(q-1)/(p-2)}$. As a corollary, we show that sufficiently dense bipartite graphs fail to be bipartite Ramsey size linear. Turning to even cycles and complete bipartite graphs, we obtain an upper bound on the multicolor bipartite Ramsey number $\operatorname{br}_k(C_{2t};K_{n,n}) \le c_{t,k}\, n^2/\log^2 n$, which follows from classical estimates for Zarankiewicz numbers together with a double-counting argument. Building on this result, we further derive a refined linear upper bound of the form $\operatorname{br}(C_{2t},G) \le \frac{m}{2} + \frac{29t\sqrt{m}}{2}$, valid for any connected bipartite graph $G$ with $m$ edges and no isolated vertices.