Owings-like theorems for infinitely many colours or finite monochromatic sets

Abstract

Inspired by Owings's problem, we investigate whether, for a given an Abelian group $G$ and cardinal numbers $\kappa ,\theta$, every colouring $c:G⟶\theta$ yields a subset $X\subseteq G$ with $|X|=\kappa$ such that $X+X$ is monochromatic. (Owings's problem asks this for $G=\mathbb{Z}$, $\theta =2$ and $\kappa ={\aleph }_0$; this is known to be false for the same $G$ and $\kappa$ but $\theta =3$.) We completely settle the question for $\kappa$ and $\theta$ both finite (by obtaining sufficient and necessary conditions for a positive answer) and for $\kappa$ and $\theta$ both infinite (with a negative answer). Also, in the case where $\theta$ is infinite but $\kappa$ is finite, we obtain some sufficient conditions for a negative answer as well as an example with a positive answer.

14 pages. Some proofs (especially in Section 2) omit various details at the request of the referee; to see more detailed proofs the reader should refer to v2