Making (dark matter) waves: Untangling wave interference for multi-streaming dark matter

TL;DR

This paper demonstrates how wave interference in a semiclassical wavefunction framework can model multi-streaming cold dark matter, revealing universal features similar to wave optics and offering new insights into cosmic structure formation.

Contribution

It introduces a wavefunction approach to capture multi-streaming dark matter dynamics and isolates single-stream components, linking wave interference to classical fluid behavior.

Findings

Wave interference encodes multi-stream dark matter phenomena.

Wave decomposition isolates classical streams from interference.

Diffraction catastrophes produce caustics analogous to dark matter density peaks.

Abstract

The classical dynamics of collisionless cold dark matter, commonly described by fluid variables or a phase-space distribution, can be captured in a single semiclassical wavefunction. We illustrate how classical multi-streaming creates wave interference in a toy model corresponding to the dynamics of the Zel'dovich approximation and link it to diffraction optics. Wave interference dresses the classical skeleton of cold dark matter with universal features akin to the physical imprints of wavelike (or fuzzy) dark matter. We untangle this wave interference to obtain single-stream wavefunctions corresponding to the classical fluid streams, by writing the wavefunction in an integral form. Our wave decomposition captures the full phase-space information and isolates the multi-stream phenomena related to vorticity and velocity dispersion. We link the wave interference features of our system to the standard forms of diffraction catastrophe integrals, which produce bright caustics in optical fields analogous to the cold dark matter density field. Our two complementary descriptions of dark matter wave-fields present rich universal features that can unlock new ways of modelling and probing wavelike dark matter on the scales of the cosmic web.