Rogues' gallery: the full freedom of the Bianchi CMB anomalies

TL;DR

This paper explores the full range of temperature and polarization anisotropy patterns in Bianchi cosmologies, highlighting how some anisotropies can evade early universe constraints and potentially explain observed CMB anomalies.

Contribution

It provides a comprehensive calculation of anisotropy patterns in Bianchi models, including linearized freedoms, and discusses their possible relevance to CMB anomalies.

Findings

Certain anisotropies can be hidden in superhorizon modes at early times.

Some patterns can produce non-trivial temperature anisotropies without conflicting with nucleosynthesis.

Future work may link these patterns to WMAP anomalies.

Abstract

Combining a recent derivation of the CMB evolution equations for homogeneous but anisotropic (Bianchi) cosmologies with an account of the full linearized dynamical freedoms available in such models, I calculate and discuss the various temperature and polarisation anisotropy patterns which may be formed. Certain anisotropies can be hidden in superhorizon modes at early times, thus avoiding any constraints from nucleosynthesis while nevertheless producing non-trivial redshift-zero temperature patterns in flat and open universes. The results are likely to be more of pedagogical than observational interest, but future work will assess whether such patterns can be matched to anomalies in WMAP results.