Vector Dark Matter from $d\geq 2$ Extra Dimensions

Abstract

In this work, we propose a new natural dark matter candidate: Kaluza-Klein towers of vectors from $d\geq 2$ extra-dimensional models. Their naturalness follows from two key features: (i) they arise unavoidably from the Kaluza-Klein decomposition of the higher-dimensional metric, and (ii) if the Standard Model is localised on a brane, they do not couple directly to it and interact only gravitationally through the other components of the higher-dimensional metric. Remarkably, the rich particle content comes with as few as a single extra parameter. We first explain the general idea for $d\geq 2$, then focus on the $d=2$ case as our benchmark scenario. We derive the field content and interactions among the model particle content, and show how the geometry of the extra dimension unitarises the relevant processes for cosmology. We then compute the multi-component relic abundances of the vectors from freeze-in and discuss the available parameter space.