Planck-PR4 anisotropy spectra show (better) consistency with General Relativity

Understand

We present the results from a series of analyses on two parametric tests of gravity that modify the growth of linear, sub-horizon matter perturbations in the $\Lambda$CDM model.

• The first test, known as the $(\mu,\Sigma)$ framework, modifies the Poisson and lensing equations from General Relativity (GR).
• The second test introduces the growth index $\gamma$, which directly affects the time evolution of matter density perturbations.
• Our study is motivated by results from the analysis of the Planck-PR3 2018 spectra, which indicate a preference for $\Sigma_0 \neq 0$ and $\gamma_0 > 0.55$, both of which deviate from the $\Lambda$CDM predictions at a significance level of $\sim 2.5\sigma$.