Novel Astrophysical Probes of Light Millicharged Fermions through Schwinger Pair Production

The extreme properties of neutron stars provide unique opportunities to put constraints on new particles and interactions. In this paper, we point out a few interesting ideas that place constraints on light millicharged fermions, with masses below around an eV, from neutron star astrophysics. The model independent bounds are obtained leveraging the fact that light millicharged fermions may be pair produced copiously via non-perturbative processes in the extreme electromagnetic environments of a neutron star, like a Magnetar. Magnetar energetics, magnetic field evolution and spin-down rates may all be influenced to various degrees by the presence of these millicharged particles.