U(1) mixing and the Weak Gravity Conjecture

TL;DR

This paper explores how the Weak Gravity Conjecture constrains dark photon models with tiny gauge couplings, predicting new physics at accessible energy scales, and discusses realizations involving extra dimensions and string theory.

Contribution

It links dark photon kinetic mixing suppression to the Weak Gravity Conjecture, predicting new physics below 100 TeV and proposing realizations with extra dimensions and string theory.

Findings

Low ultraviolet cut-offs for dark photons with tiny couplings.

Mixing angle of ~10^{-15} implies new physics below 100 TeV.

Realizations involve six large extra dimensions and a 100 TeV string scale.

Abstract

Tiny values for gauge couplings of dark photons allow to suppress their kinetic mixing with ordinary photons. We point out that the Weak Gravity Conjecture predicts consequently low ultraviolet cut-offs where new degrees of freedom might appear. In particular, a mixing angle of $\mathcal{O}(10^{-15})$, required in order to fit the excess reported by XENON1T, corresponds to new physics below $\mathcal{O}(100)$ TeV, thus accessible at a Future Circular Collider. We show that possible realizations are provided by compactifications with six large extra dimensions and a string scale of order $\mathcal{O}(100)$ TeV.