Light hidden-sector U(1)s in string compactifications

TL;DR

This paper surveys light hidden-sector U(1) gauge bosons that arise in string compactifications and their kinetic mixing with the Standard Model hypercharge. It contrasts heterotic and Type II scenarios, detailing methods to compute mixing and the roles of RR U(1)s and D-brane U(1)s. The analysis yields a range of plausible mixing strengths, from ~10^-4 in simple heterotic setups to ~10^-3 or smaller values depending on moduli stabilization and mass-generation mechanisms such as Stückelberg mixing. The authors discuss implications for dark matter, cosmology, and collider phenomenology, arguing that near-future experiments could probe these hidden sectors.

Abstract

We review the case for light U(1) gauge bosons in the hidden-sector of heterotic and type II string compactifications, present estimates of the size of their kinetic mixing with the visible-sector hypercharge U(1), and discuss their possibly very interesting phenomenological consequences in particle physics and cosmology.