Scale-dependent dipolar modulation and the quadrupole-octopole alignment in the CMB temperature

TL;DR

This paper proposes a scale-dependent dipolar modulation model for the CMB, which better explains the observed anomalies like the quadrupole-octopole alignment, suggesting a correlation between these features.

Contribution

It introduces a scale-dependent dipolar modulation model that links CMB anomalies and shows improved fit over previous models based on Bayesian analysis.

Findings

The scale-dependent model fits the CMB data better than the scale-independent one.

Large dipolar modulation amplitude at low multipoles correlates with anomalies.

The model increases the significance of the quadrupole-octopole alignment by 80%.

Abstract

The connection between the dipolar modulation asymmetry and the quadrupole-octopole alignment in the CMB is studied in this work. First, a generalization of the dipolar modulation model is proposed by considering that the amplitude may depend on the scale. As derived from a Bayesian inference analysis, this model fits the CMB data better than the scale-independent one. As an extension of the standard model, the scale-dependent dipolar modulation shows comparable evidence to the standard isotropic model in the large scales ($\ell_\mathrm{max} \leq 64$). The posterior distribution of the parameters of the scale-dependent model suggests that the amplitude of the dipolar modulation is large at the lowest multipoles. This large asymmetry induces a detectable correlation between the quadrupole and the octopole. The significance of the quadrupole-octopole alignment is analyzed under the assumption that the Universe has a scale-dependent dipolar modulation. The three alignment estimators considered in this paper show an increment of $80\%$ in the p-value, showing a clear correlation between these two CMB anomalies. Within this new scenario, only one of the alignment estimators is still below the $1\%$ probability level.