# Bounding milli-magnetically charged particles with magnetars

## TL;DR

This paper derives model-independent bounds on milli-magnetically charged particles using magnetar magnetic field observations, showing such charges must be smaller than 10^{-18} across various masses due to Schwinger pair production effects.

## Contribution

It provides the first model-independent constraints on milli-magnetic charges from astrophysical observations of magnetars.

## Key findings

- Milli-magnetic charges must be less than 10^{-18} for a wide mass range.
- Magnetar magnetic fields disfavor larger milli-magnetic charges due to Schwinger pair production.
- Constraints are derived without relying on specific particle models.

## Abstract

Milli-magnetically charged particles generically appear in scenarios with kinetic mixing. We present model independent bounds on these particles coming from magnetars. Schwinger pair production discharges the magnetic field of the magnetar. Thus the existence of large magnetic fields at magnetars place strong bounds on the milli-magnetic charge to be smaller than $10^{-18}$ over a large mass range.