Multipole decomposition of redshift drift -- model independent mapping of the expansion history of the Universe

TL;DR

This paper presents a model-independent multipole decomposition of redshift drift, revealing its complex relationship with the universe's expansion and predicting anisotropic effects in observations.

Contribution

It introduces a multipole series approach to analyze redshift drift, highlighting the influence of local structures and anisotropies on measurements.

Findings

Redshift drift is not a straightforward measure of average cosmic expansion.

Presence of dipolar and quadrupolar offsets in redshift drift signals.

Redshift drift analysis must account for local anisotropies and structures.

Abstract

We consider redshift drift in a general space-time as expressed in terms of physically interpretable multipole series. An important realisation from the derived results is that redshift drift cannot in general be thought of as a direct probe of the average expansion rate of the Universe due to the presence of structure along the light beams from the astrophysical sources to the observer. We also predict the general presence of a dipolar and a quadrupolar offset in the detection of redshift drift for observers placed in locally anisotropic environments.