Cosmological Two-stream Instability

TL;DR

This paper demonstrates that the two-stream instability, known in plasma physics, can occur in cosmological models with two interpenetrating fluids during certain transition periods, but is eventually suppressed by cosmic expansion.

Contribution

It introduces the first cosmological context for two-stream instability using a new formalism for two-fluid models with relative flow.

Findings

Two-stream instability can be triggered during fluid domination transitions.

Cosmological expansion suppresses the instability over time.

The formalism models interpenetrating fluids with relative flow in cosmology.

Abstract

Two-stream instability requires, essentially, two things to operate: a relative flow between two fluids and some type of interaction between them. In this letter we provide the first demonstration that this mechanism may be active in a cosmological context. Building on a recently developed formalism for cosmological models with two, interpenetrating fluids with a relative flow between them, we show that two-stream instability may be triggered during the transition from one fluid domination to the other. We also demonstrate that the cosmological expansion eventually shuts down the instability by driving to zero the relativeflow and the coupling between the two fluids.