Structure Formation with Dark Magnetohydrodynamics

TL;DR

This paper explores how dark magnetic fields influence dark matter structure formation, showing they modify the matter power spectrum and could be tested by future high-resolution cosmological observations.

Contribution

It presents the first magnetohydrodynamic study of gravitational collapse in a dark U(1)_D model, revealing anisotropic pressure effects on structure formation.

Findings

Dark magnetic fields generate anisotropic pressure affecting the Jeans scale.

Small-scale power is suppressed in a direction-dependent manner.

Future observations can test dark charge-to-mass ratios in the range 10^{-20} to 10^{-14} GeV^{-1}.

Abstract

Long-range interactions in the dark sector can give rise to collective plasma phenomena that are capable of modifying the evolution of dark matter halos. We present the first study of gravitational collapse in a secluded dark $U(1)_D$ model using a magnetohydrodynamic description of the dark matter. We show that dark magnetic fields generate an anisotropic pressure that alters the Jeans scale and suppresses small-scale power in a direction-dependent manner. For a range of primordial magnetic spectral indices, this effect produces distinctive modifications to the linear matter power spectrum. We find that current observations cannot yet constrain viable dark magnetic fields, as CMB tensor modes mostly provide more stringent constraints. Nevertheless, forthcoming high-resolution probes of the matter power spectrum (CMB-HD lensing, HERA, and EDGES) will be able to test these predictions and are sensitive to dark charge-to-mass ratios in the range $10^{-20}\,\text{GeV}^{-1}\lesssim q_\chi/m_\chi\lesssim 10^{-14}\,\text{GeV}^{-1}$.