Estimating CDM Particle Trajectories in the Mildly Non-Linear Regime of Structure Formation. Implications for the Density Field in Real and Redshift Space

TL;DR

This paper introduces an improved approximation method for modeling Cold Dark Matter (CDM) particle trajectories in the mildly non-linear regime, enhancing density field predictions and enabling faster cosmological analyses.

Contribution

The authors develop a new approximation based on Lagrangian Perturbation Theory that outperforms standard methods in predicting density and momentum fields in real and redshift space.

Findings

Achieves >95% cross-correlation with non-linear density down to smaller scales.

Enables an order of magnitude speed-up in cosmological parameter scans.

Improves accuracy over linear and standard perturbation theories.

Abstract

We obtain approximations for the CDM particle trajectories starting from Lagrangian Perturbation Theory. These estimates for the CDM trajectories result in approximations for the density in real and redshift space, as well as for the momentum density that are better than what standard Eulerian and Lagrangian perturbation theory give. For the real space density, we find that our proposed approximation gives a good cross-correlation (>95%) with the non-linear density down to scales almost twice smaller than the non-linear scale, and six times smaller than the corresponding scale obtained using linear theory. This allows for a speed-up of an order of magnitude or more in the scanning of the cosmological parameter space with N-body simulations for the scales relevant for the baryon acoustic oscillations. Possible future applications of our method include baryon acoustic peak reconstruction, building mock galaxy catalogs, momentum field reconstruction.