Leakage of power from dipole to higher multipoles due to non-symmetric WMAP beam

TL;DR

This paper investigates how non-symmetric beam shapes in WMAP and Planck satellites can cause the dominant dipole signal to leak into higher multipoles, potentially explaining observed anomalies in the CMB quadrupole.

Contribution

It quantifies the power leakage from the dipole to higher multipoles due to asymmetric beams and assesses its impact on observed CMB anomalies.

Findings

Significant dipole power leaks into quadrupole due to beam asymmetry.

The quadrupole orientation from leakage closely matches observed data.

Upper limits on beam asymmetry parameters are established for Planck.

Abstract

A number of studies of WMAP and Planck claimed the low multipole (specially quadrupole) power deficiency in CMB power spectrum. Anomaly in the orientations of the low multipoles have also been claimed. There is a possibility that the power deficiency at low multipoles may not be of primordial origin and is only an observation artifact coming from the scan procedure adapted in the WMAP or Planck satellites. Therefore, it is always important to investigate all the observational artifacts that can mimic them. The CMB dipole which is much higher than the quadrupole, can leak to the higher multipoles due to the non-symmetric beam shape of the WMAP or Planck. We observe that a non-negligible amount of power from the dipole can get transferred to the quadrupole and the higher multipoles due to the non-symmetric beam shapes and contaminate the observed measurements. The orientation of the quadrupole generated by this power transfer is surprisingly very close to the quadrupole observed from the WMAP and Planck maps. However, our analysis shows that the orientation of the quadrupole can not be explained using only the dipole power leakage. In this paper we calculate the amount of quadrupole power leakage for different WMAP bands. For Planck we present the results in terms of upper limits on asymmetric beam parameters that can lead to significant amount of power leakage.