Expected redshift drift for tilted observers

TL;DR

This paper calculates the expected redshift drift for observers with peculiar motion in cosmology, revealing how tilt and anisotropic effects influence the standard signal in different cosmological models.

Contribution

It derives a covariant formalism for redshift drift for tilted observers, including directional corrections from peculiar kinematics, extending previous comoving observer analyses.

Findings

Tilted observers experience directional corrections to redshift drift.

In Einstein--de Sitter universe, tilt effects are purely kinematic.

In DM, anisotropic corrections deform the standard drift signal.

Abstract

Redshift drift is usually discussed for observers comoving with the cosmological background, but realistic observations are made by observers with nonzero peculiar motion. In this work, we calculate the expected redshift drift for tilted observers within the covariant \(1+3\) formalism. Starting from the exact redshift measured in the tilted frame, we derive the corresponding drift as an FLRW background term plus a directional correction driven by the observer's peculiar kinematics, encoded through peculiar expansion, projected shear, and projected acceleration along the line of sight. We analyse first an Einstein--de Sitter (EdS) background, which isolates the purely kinematic effect of tilt in the absence of background acceleration, and then extend the calculation to \(\Lambda\)CDM in order to quantify how the same anisotropic corrections deform the standard drift signal in the concordance model.