Exploring the Growth Index $\gamma_L$: Insights from Different CMB Dataset Combinations and Approaches

TL;DR

This paper investigates the growth index $mma_L$ using various CMB datasets and analysis methods, revealing deviations from the standard model with Planck data but consistency with ground-based telescopes, highlighting dataset impacts.

Contribution

It compares two different CAMB approaches to analyze the growth index and demonstrates how additional datasets like CMB lensing can reconcile deviations from the mbda CDM model.

Findings

Deviations from mbda CDM value of 0.55 with Planck data in both methods.

CMB lensing data helps align mma_L with mbda CDM.

Ground-based telescopes ACT and SPT agree with mbda CDM value.

Abstract

In this study we investigate the growth index $\gamma_L$, which characterizes the growth of linear matter perturbations, while analysing different cosmological datasets. We compare the approaches implemented by two different patches of the cosmological solver CAMB: MGCAMB and CAMB_GammaPrime_Growth. In our analysis we uncover a deviation of the growth index from its expected $\Lambda$CDM value of $0.55$ when utilizing the Planck dataset, both in the MGCAMB case and in the CAMB_GammaPrime_Growth case, but in opposite directions. This deviation is accompanied by a change in the direction of correlations with derived cosmological parameters. However, the incorporation of CMB lensing data helps reconcile $\gamma_L$ with its $\Lambda$CDM value in both cases. Conversely, the alternative ground-based telescopes ACT and SPT consistently yield growth index values in agreement with $\gamma_L=0.55$. We conclude that the presence of the A$_{\mathrm{lens}}$ problem in the Planck dataset contributes to the observed deviations, underscoring the importance of additional datasets in resolving these discrepancies.