Late Kinetic Decoupling of Light Magnetic Dipole Dark Matter

TL;DR

This paper investigates how light magnetic dipole dark matter remains in thermal equilibrium longer than traditional models, resulting in larger primordial structures and affecting early universe formation.

Contribution

It demonstrates that magnetic dipole dark matter can stay kinetically coupled until electron-positron annihilation, leading to larger initial dark matter structures.

Findings

Dark matter remains in thermal equilibrium until electron-positron annihilation.

Minimum protohalo mass is thousands of solar masses.

Contrasts with weak scale dark matter scenarios.

Abstract

We study the kinetic decoupling of light (lesssim 10 GeV) magnetic dipole dark matter (DM). We find that present bounds from collider, direct DM searches, and structure formation allow magnetic dipole DM to remain in thermal equilibrium with the early universe plasma until as late as the electron-positron annihilation epoch. This late kinetic decoupling leads to a minimal mass for the earliest dark protohalos of thousands of solar masses, in contrast to the conventional weak scale DM scenario where they are of order 10^{-6} solar masses.