Impact of Low ell's on Large Scale Structure Anomalies

TL;DR

This study investigates the CMB lensing anomaly, revealing it is driven by low multipole data and that excluding these points favors the standard cosmological model, reducing several tensions.

Contribution

It demonstrates that the CMB lensing anomaly is primarily caused by low multipole data and shows that removing these data points aligns observations with the standard cosmological model.

Findings

The lensing anomaly is driven by low multipoles ($  30$).

Excluding low multipoles favors CDM over extended models.

Removing low multipoles reduces the $S_8$ and lensing anomalies.

Abstract

We scrutinize the reported lensing anomaly of the CMB by considering several phenomenological modifications of the lensing consistency parameter, $A_{\rm L}$. Considering Planck spectra alone, we find statisically significant evidence for scale dependence (`running') of $A_{\rm L}$. We then demonstrate that the anomaly is entirely driven by Planck's low multipoles, $\ell \leq 30$. When these data points are excluded a joint analysis with several other datasets clearly favors $\Lambda$CDM over the extended $\Lambda \rm CDM+A_L$ model. Not only that the lensing anomaly and low $\ell$ anomaly of the CMB go away in this case, but also the $S_8$ tension is ameliorated, and only the Hubble tension persists.