Exploring the growth index γL : Insights from different CMB dataset combinations and approaches

In this study we investigate the growth index <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>γ</a:mi><a:mi>L</a:mi></a:msub></a:math>, 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 : and __. In our analysis we uncover a deviation of the growth index from its expected <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi mathvariant="normal">Λ</c:mi><c:mi>CDM</c:mi></c:math> value of 0.55 when utilizing the Planck dataset, both in the case and in the __ 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 <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:msub><f:mi>γ</f:mi><f:mi>L</f:mi></f:msub></f:math> with its <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mi mathvariant="normal">Λ</h:mi></h:math>-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 <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msub><k:mi>γ</k:mi><k:mi>L</k:mi></k:msub><k:mo>=</k:mo><k:mn>0.55</k:mn></k:math>. We conclude that the presence of the <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:msub><m:mrow><m:mi mathvariant="normal">A</m:mi></m:mrow><m:mrow><m:mi>lens</m:mi></m:mrow></m:msub></m:math> problem in the Planck dataset contributes to the observed deviations, underscoring the importance of additional datasets in resolving these discrepancies. Published by the American Physical Society 2024