Testing the $\mathbf{\Lambda}$CDM Cosmological Model with Forthcoming Measurements of the Cosmic Microwave Background with SPT-3G

TL;DR

This paper forecasts how upcoming SPT-3G measurements will improve constraints on the Lambda-CDM cosmological model by analyzing CMB data across different sky regions and frequencies, enabling more precise tests of cosmology.

Contribution

It introduces a novel method for covariance matrix estimation and demonstrates how SPT-3G data can independently and jointly constrain Lambda-CDM parameters with greater precision than Planck.

Findings

SPT-3G data can constrain cosmological parameters up to twice as precisely as Planck.

Joint analysis of SPT-3G and Planck improves constraints on Lambda-CDM extensions.

Different angular scales and polarization levels provide additional tests of the standard model.

Abstract

We forecast constraints on cosmological parameters enabled by three surveys conducted with SPT-3G, the third-generation camera on the South Pole Telescope. The surveys cover separate regions of 1500, 2650, and 6000 ${\rm deg}^{2}$ to different depths, in total observing 25% of the sky. These regions will be measured to white noise levels of roughly 2.5, 9, and 12 $\mu{\rm K-arcmin}$, respectively, in CMB temperature units at 150 GHz by the end of 2024. The survey also includes measurements at 95 and 220 GHz, which have noise levels a factor of ~1.2 and 3.5 times higher than 150 GHz, respectively, with each band having a polarization noise level ~$\sqrt{\text{2}}$ times higher than the temperature noise. We use a novel approach to obtain the covariance matrices for jointly and optimally estimated gravitational lensing potential bandpowers and unlensed CMB temperature and polarization bandpowers. We demonstrate the ability to test the $\Lambda{\rm CDM}$ model via the consistency of cosmological parameters constrained independently from SPT-3G and Planck data, and consider the improvement in constraints on $\Lambda{\rm CDM}$ extension parameters from a joint analysis of SPT-3G and Planck data. The $\Lambda{\rm CDM}$ cosmological parameters are typically constrained with uncertainties up to ~2 times smaller with SPT-3G data, compared to Planck, with the two data sets measuring significantly different angular scales and polarization levels, providing additional tests of the standard cosmological model.