An Origami Approximation to the Cosmic Web

TL;DR

This paper introduces an origami-inspired model of cosmic web formation, where a non-stretching dark matter sheet folds to form structures, simplifying the understanding of phase-space geometry and galaxy spin correlations.

Contribution

It presents a novel origami approximation for cosmic web formation, allowing easier analysis of phase-space structures and galaxy spin correlations.

Findings

The origami model produces convex polyhedral voids and filamentary structures.

It enables new kinematic models of velocity fields in cosmic structures.

The approach simplifies understanding of complex phase-space geometries.

Abstract

The powerful Lagrangian view of structure formation was essentially introduced to cosmology by Zel'dovich. In the current cosmological paradigm, a dark-matter-sheet 3D manifold, inhabiting 6D position-velocity phase space, was flat (with vanishing velocity) at the big bang. Afterward, gravity stretched and bunched the sheet together in different places, forming a cosmic web when projected to the position coordinates. Here, I explain some properties of an origami approximation, in which the sheet does not stretch or contract (an assumption that is false in general), but is allowed to fold. Even without stretching, the sheet can form an idealized cosmic web, with convex polyhedral voids separated by straight walls and filaments, joined by convex polyhedral nodes. The nodes form in 'polygonal' or 'polyhedral' collapse, somewhat like spherical/ellipsoidal collapse, except incorporating simultaneous filament and wall formation. The origami approximation allows phase-space geometries of nodes, filaments, and walls to be more easily understood, and may aid in understanding spin correlations between nearby galaxies. This contribution explores kinematic origami-approximation models giving velocity fields for the first time.