Precise cosmological parameter estimation using CosmoRec

TL;DR

This paper evaluates the impact of advanced recombination modeling with CosmoRec on precise cosmological parameter estimation from CMB data, highlighting the importance of including physical processes for unbiased results.

Contribution

It introduces the use of CosmoRec for model-by-model recombination calculations, assessing biases from neglected physics in parameter estimation.

Findings

Recombination corrections significantly affect parameter biases.

Model-by-model recombination calculations improve accuracy.

Redshift-dependent corrections may suffice for practical purposes.

Abstract

We use the new cosmological recombination code, CosmoRec, for parameter estimation in the context of (future) precise measurements of the CMB temperature and polarization anisotropies. We address the question of how previously neglected physical processes in the recombination model of Recfast affect the determination of key cosmological parameters, for the first time performing a model-by-model computation of the recombination problem. In particular we ask how the biases depend on different combinations of parameters, e.g. when varying the helium abundance or the effective number of neutrino species in addition to the standard six parameters. We also forecast how important the recombination corrections are for a combined Planck, ACTPol and SPTpol data analysis. Furthermore, we ask which recombination corrections are really crucial for CMB parameter estimation, and whether an approach based on a redshift-dependent correction function to Recfast is sufficient in this context.