# Towards Schwinger production of magnetic monopoles in heavy-ion collisions

## TL;DR

This paper reviews electromagnetic fields in heavy-ion collisions and calculates the monopole pair production cross section using a non-perturbative method, indicating potential for stronger monopole mass bounds.

## Contribution

It introduces a first-principles calculation of monopole production in inhomogeneous fields using the worldline instanton method, accounting for all magnetic charges.

## Key findings

- Spacetime inhomogeneity enhances monopole production cross section.
- The Keldysh parameter governs the production rate independently of collision energy.
- Finite monopole size and computational complexity limit current applicability.

## Abstract

Magnetic monopoles may be produced by the Schwinger effect in the strong magnetic fields of peripheral heavy-ion collisions. We review the form of the electromagnetic fields in such collisions and calculate from first principles the cross section for monopole pair production. Using the worldline instanton method, we work to all orders in the magnetic charge, and hence are not hampered by the breakdown of perturbation theory. Our result depends on the spacetime inhomogeneity through a single dimensionless parameter, the Keldysh parameter, which is independent of collision energy for a given monopole mass. For realistic heavy-ion collisions, the computational cost of the calculation becomes prohibitive and the finite size of the monopoles needs to be taken into account, and therefore our current results are not applicable to them. Nonetheless, our results show that the spacetime dependence enhances the production cross section and would therefore lead to stronger monopole mass bounds than in the constant-field case.