The Signature of Proper Motion in the Microwave Sky

TL;DR

This paper predicts how the motion of observers relative to the cosmic rest frame affects microwave background anisotropies, providing testable signals for future satellite data to constrain cosmological models.

Contribution

It calculates the expected dipole and off-diagonal correlations in the microwave sky caused by observer motion, which were previously unquantified.

Findings

Motion induces detectable dipole anisotropy.

Motion causes off-diagonal correlations in multipole moments.

Predicted signals are within Planck satellite detection capabilities.

Abstract

The cosmic microwave background radiation defines a preferred cosmic rest frame, and inflationary cosmological theories predict that the microwave background temperature fluctuations should be statistically isotropic in this rest frame. For observers moving with respect to the rest frame, the temperature fluctuations will no longer be isotropic, due to the preferred direction of motion. The most prominent effect is a dipole temperature variation, which has long been observed with an amplitude of a part in a thousand of the mean temperature. An observer's velocity with respect to the rest frame will also induce changes in the angular correlation function and creation of non-zero off-diagonal correlations between multipole moments. We calculate both of these effects, which are part-in-a-thousand corrections to the rest frame power spectrum and correlation function. Both should be detectable in future full-sky microwave maps from the Planck satellite. These signals will constrain cosmological models in which the cosmic dipole arises partly from large-scale isocurvature perturbations, as suggested by recent observations.