CMB low multipole alignments in the $\mathbf{\Lambda}$CDM and Dipolar models

TL;DR

This study examines whether the dipolar model can explain low multipole alignments in the CMB and finds it does not improve upon the standard b5CDM model, with anomalies present in both.

Contribution

The paper demonstrates that the dipolar model does not better explain CMB low multipole alignments compared to b5CDM, challenging its effectiveness in addressing large-scale anisotropies.

Findings

Low b5 alignments are anomalous in b5CDM data.

The dipolar model shows similar anomalies as b5CDM.

Dipolar model does not improve fit to CMB anomalies.

Abstract

The dipolar model \cite{Gordon:2005ai} has attracted much interest because it may phenomenologically explain the CMB hemispherical power asymmetry found in the WMAP and Planck data. Since such a model explicitly breaks isotropy at large angular scales it is natural to wonder whether it can also explain other CMB directional anomalies. Focusing on the low $\ell$ alignments and assuming $\Lambda$CDM, we confirm that the quadrupole/octupole and the dipole/quadrupole/octupole alignments are anomalous with a significance up to $99.9\%$ C.L., for both WMAP and Planck data. Moreover, we show for the first time that such features are anomalous also in the dipolar model, roughly at the same level as in $\Lambda$CDM. We conclude that the dipolar model does not provide a better fit to the data than the $\Lambda$CDM.