Exploring the growth index γ L : insights from different CMB dataset combinations and approaches

Abstract

In this study we investigate the growth index γ 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 Λ 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 cosmic microwave background lensing data helps reconcile γ L with its Λ -cold dark matter value in both cases. Conversely, the alternative ground-based telescopes Atacama Cosmology Telescope and South Pole Telescope consistently yield growth index values in agreement with γ L = 0.55 . We conclude that the presence of the A lens problem in the Planck dataset contributes to the observed deviations, underscoring the importance of additional datasets in resolving these discrepancies.