Owings-like theorems for infinitely many colours or finite monochromatic sets (2402.13124v4)

Abstract: Inspired by Owings's problem, we investigate whether, for a given an Abelian group $G$ and cardinal numbers $\kappa,\theta$, every colouring $c:G\longrightarrow\theta$ 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.