Dark plasmas in the nonlinear regime: constraints from particle-in-cell simulations

TL;DR

This paper uses particle-in-cell simulations to explore how dark matter with long-range interactions can form plasma-like instabilities, affecting astrophysical observations and constraining dark sector properties.

Contribution

First dedicated particle-in-cell simulations of dark matter plasma instabilities, revealing their nonlinear evolution and impact on astrophysical constraints.

Findings

Dark instabilities create dark electromagnetic inhomogeneities.

These inhomogeneities act as scattering sites, increasing effective cross-section.

Extended limits on dark charge-to-mass ratio by over ten orders of magnitude.

Abstract

If the dark sector possesses long-range self-interactions, these interactions can source dramatic collective instabilities even in astrophysical settings where the collisional mean free path is long. Here, we focus on the specific case of dark matter halos composed of a dark $U(1)$ gauge sector undergoing a dissociative cluster merger. We study this by performing the first dedicated particle-in-cell plasma simulations of interacting dark matter streams, tracking the growth, formation, and saturation of instabilities through both the linear and nonlinear regimes. We find that these instabilities give rise to local (dark) electromagnetic inhomogeneities that serve as scattering sites, inducing an effective dynamic collisional cross-section. Mapping this effective cross-section onto existing results from large-scale simulations of the Bullet Cluster, we extend the limit on the dark charge-to-mass ratio by over ten orders of magnitude. Our results serve as a simple example of the rich phenomenology that may arise in a dark sector with long-range interactions and motivate future dedicated study of such ``dark plasmas.''