Milli-Charged Dark Matter in Quantum Gravity and String Theory

TL;DR

This paper investigates milli-charged dark matter within string theory, revealing that such charges originate solely from kinetic mixing and necessitate multiple massless gauge bosons, challenging previous assumptions about irrational charges in quantum gravity.

Contribution

It demonstrates that milli-charges in string theory arise only through kinetic mixing and require at least two massless gauge bosons, clarifying the underlying structure of U(1) interactions.

Findings

Milli-charges are generated exclusively via kinetic mixing.

At least two massless gauge bosons are necessary for milli-charges.

The structure of the U(1) mass matrix constrains milli-charge formation.

Abstract

We examine the milli-charged dark matter scenario from a string theory perspective. In this scenario, kinetic and mass mixings of the photon with extra U(1) bosons are claimed to give rise to small electric charges, carried by dark matter particles, whose values are determined by continuous parameters of the theory. This seems to contradict folk theorems of quantum gravity that forbid the existence of irrational charges in theories with a single massless gauge field. By considering the underlying structure of the U(1) mass matrix that appears in type II string compactifications, we show that milli-charges arise exclusively through kinetic mixing, and require the existence of at least two exactly massless gauge bosons.