Detecting CMB modulations and non-Gaussianities from power multipoles

TL;DR

This paper introduces CMB power multipoles as a new, precise method to measure and analyze modulations and non-Gaussianities in the cosmic microwave background, surpassing current observational constraints.

Contribution

It proposes a novel approach using spherical harmonic decomposition of squared temperature fluctuations to improve accuracy in detecting CMB modulations and non-Gaussianities.

Findings

CMB power multipoles enable direct and indirect measurements of modulations.

The method achieves higher theoretical accuracy than current Planck constraints.

Improves dipole modulation accuracy by a factor of ten.

Abstract

By decomposing the CMB temperature fluctuations \emph{squared} into spherical harmonics, we can define the \emph{CMB power multipoles} as the fundamental observables to quantify any generic modulations in the CMB. This allows for simple direct measurements for the CMB modulations, and also indirect measurements for the CMB trispectrum, which fully determines the CMB modulations in a statistically isotropic universe. The CMB power multipoles can reach the theoretical accuracies higher than the current constraints from Planck observations. The theoretical accuracy for the dipole modulation, $A\sim0.0015$, receives $\sim 10$ times improvement; higher $l$ modulations have even higher accuracies. This calls for practical observational studies of its possible improvements on the CMB modulation and non-Gaussianity constraints.