Shell-crossing in a $\Lambda$CDM Universe

TL;DR

This paper investigates the convergence of high-order Lagrangian perturbation theory near the first shell-crossing in a realistic 3D universe, revealing that convergence-limiting singularities occur after shell-crossing.

Contribution

It numerically implements all-order recursion relations for matter trajectories in 3D, establishing the convergence properties of LPT at shell-crossing up to 40th order.

Findings

LPT series converges at shell-crossing for high orders

Singularities limiting convergence occur after shell-crossing

Convergence behavior characterized by high-order studies

Abstract

Perturbation theory is an indispensable tool for studying the cosmic large-scale structure, and establishing its limits is therefore of utmost importance. One crucial limitation of perturbation theory is shell-crossing, which is the instance when cold-dark-matter trajectories intersect for the first time. We investigate Lagrangian perturbation theory (LPT) at very high orders in the vicinity of the first shell-crossing for random initial data in a realistic three-dimensional Universe. For this we have numerically implemented the all-order recursion relations for the matter trajectories, from which the convergence of the LPT series at shell-crossing is established. Convergence studies performed up to the 40th order reveal the nature of the convergence-limiting singularities. These singularities are not the well-known density singularities at shell-crossing but occur at later times when LPT already ceased to provide physically meaningful results.