Linear-sized minors with given edge density

Abstract

It is proved that for every $\varepsilon>0$, there exists $K>0$ such that for every integer $t\ge2$, every graph with chromatic number at least $Kt$ contains a minor with $t$ vertices and edge density at least $1-\varepsilon$. Indeed, building on recent work of Delcourt and Postle on linear Hadwiger's conjecture, for $\varepsilon\in(0,\frac{1}{256})$ we can take $K=C\log\log(1/\varepsilon)$ where $C>0$ is a universal constant, which extends their recent $O(t\log\log t)$ bound on the chromatic number of graphs with no $K_t$ minor.