Dark sector domain walls could explain the observed planes of satellites

TL;DR

This paper proposes that domain walls from symmetry-breaking scalar fields could cause satellite galaxies to align in planes, offering a new physics explanation for the observed satellite planes without removing dark matter.

Contribution

It introduces a novel mechanism involving domain walls and fifth forces that can produce satellite plane alignments, differing from standard dark matter explanations.

Findings

Simulations show satellites can be confined to domain wall planes due to fifth forces.

Planarity metrics can detect the influence of domain walls on satellite distributions.

This mechanism provides a potential new physics explanation consistent with dark matter presence.

Abstract

The observed `planes of satellites' around the Milky Way and other nearby galaxies are notoriously difficult to explain under the $\Lambda$CDM paradigm. Here, we propose an alternative solution: domain walls arising in theories with symmetry-breaking scalar fields coupled to matter. Because of the matter coupling, satellite galaxies experience fifth forces as they pass through domain walls, leading to a subset of satellites with orbits confined to the domain wall plane. We demonstrate this effect using simple simulations of a toy model comprising point-like satellites and an infinite domain wall, and explore the efficacy of various planarity metrics in detecting this effect. We believe this is the first potential `new physics' explanation for the observed planes of satellites which does not do away with dark matter.