On the consistency of $\Lambda$CDM with CMB measurements in light of the latest Planck, ACT, and SPT data

Using Gaussian Processes we perform a thorough, non-parametric consistency test of the $\Lambda$CDM model when confronted with state-of-the-art TT, TE, and EE measurements of the anisotropies in the Cosmic Microwave Background by the Planck, ACT, and SPT collaborations. Using $\Lambda$CDM's best-fit predictions to the TTTEEE data from Planck, we find no statistically significant deviations when looking for signatures in the residuals across the different datasets. The results of SPT are in good agreement with the $\Lambda$CDM best-fit predictions to the Planck data, while the results of ACT are only marginally consistent. However, when using the best-fit predictions to CamSpec -- a recent reanalysis of the Planck data -- as the mean function, we find larger discrepancies between the datasets. Our analysis also reveals an interesting feature in the polarisation (EE) measurements from the CamSpec analysis, which could be explained by a slight underestimation of the covariance matrix. Interestingly, the disagreement between CamSpec and Planck/ACT is mainly visible in the residuals of the TT spectrum, the latter favoring a scale-invariant tilt $n_s\simeq1$, which is consistent with previous findings from parametric analyses. We also report some features in the EE measurements captured both by ACT and SPT which are independent of the chosen mean function and could be hinting towards a common physical origin. For completeness, we repeat our analysis using the best-fit spectra to ACT+WMAP as the mean function. Finally, we test the internal consistency of the Planck data alone by studying the high and low-$\ell$ ranges separately, finding no discrepancy between small and large angular scales.