Density theorems for bipartite graphs and related Ramsey-type results

In this paper, we present several density-type theorems which show how to find a copy of a sparse bipartite graph in a graph of positive density. Our results imply several new bounds for classical problems in graph Ramsey theory and improve and generalize earlier results of various researchers. The proofs combine probabilistic arguments with some combinatorial ideas. In addition, these techniques can be used to study properties of graphs with a forbidden induced subgraph, edge intersection patterns in topological graphs, and to obtain several other Ramsey-type statements

Decomposition of bounded degree graphs into C4C_4-free subgraphs

We prove that every graph with maximum degree $\Delta$ admits a partition of its edges into $O(\sqrt{\Delta})$ parts (as $\Delta\to\infty$) none of which contains $C_4$ as a subgraph. This bound is sharp up to a constant factor. Our proof uses an iterated random colouring procedure.Comment: 8 pages; to appear in European Journal of Combinatoric

A lifting of graphs to 3-uniform hypergraphs, its generalization, and further investigation of hypergraph Ramsey numbers

Ramsey theory has posed many interesting questions for graph theorists that have yet to besolved. Many different methods have been used to find Ramsey numbers, though very feware actually known. Because of this, more mathematical tools are needed to prove exactvalues of Ramsey numbers and their generalizations. Budden, Hiller, Lambert, and Sanfordhave created a lifting from graphs to 3-uniform hypergraphs that has shown promise. Theybelieve that many results may come of this lifting, and have discovered some themselves.This thesis will build upon their work by considering other important properties of theirlifting and analogous liftings for higher-uniform hypergraphs. We also consider ways inwhich one may extend many known results in Ramsey Theory for graphs to the r-uniformhypergraph setting