# Generating Approximate Halo Catalogs for Blind Challenges in Precision Cosmology

## TL;DR

This paper introduces a method to efficiently generate approximate dark-matter halo catalogs for different cosmologies using transfer functions, enabling high-precision cosmological analyses with minimal simulations.

## Contribution

The authors develop a transfer function approach to modify existing halo catalogs for new cosmologies, reducing computational costs in precision cosmology.

## Key findings

- Achieves 0.1% accuracy in real-space power spectrum for 1% change in σ8
- Maintains accuracy in redshift-space monopole and quadrupole
- Results surpass sample variance limits in large simulation boxes

## Abstract

We present a method for generating suites of dark-matter halo catalogs with only a few $N$-body simulations, focusing on making small changes to the underlying cosmology of a simulation with high precision. In the context of blind challenges, this allows us to reuse a simulation by giving it a new cosmology after the original cosmology is revealed. Starting with full $N$-body realizations of an original cosmology and a target cosmology, we fit a transfer function that displaces halos in the original so that the galaxy/HOD power spectrum matches that of the target cosmology. This measured transfer function can then be applied to a new realization of the original cosmology to create a new realization of the target cosmology. For a 1% change in $\sigma_8$, we achieve 0.1% accuracy to $k = 1h\,\mathrm{Mpc}^{-1}$ in the real-space power spectrum; this degrades to 0.3% when the transfer function is applied to a new realization. We achieve similar accuracy in the redshift-space monopole and quadrupole. In all cases, the result is better than the sample variance of our $1.1h^{-1}\,\mathrm{Gpc}$ simulation boxes.