Kaluza-Klein anisotropy in the CMB

TL;DR

This paper investigates how extra-dimensional effects in Kaluza-Klein theories can influence cosmic microwave background anisotropies, showing that graviton stresses can sustain observable shear anisotropy levels and placing limits on initial anisotropies.

Contribution

It demonstrates that 5D Kaluza-Klein graviton stresses can prolong shear anisotropy decay, affecting CMB observations and constraining initial anisotropy levels.

Findings

KK graviton stresses can sustain shear anisotropy to observable levels.

CMB anisotropies can constrain initial KK-induced anisotropy.

Initial shear distortions of ~10^{-3} are compatible with observed CMB signals.

Abstract

We show that 5-dimensional Kaluza-Klein graviton stresses can slow the decay of shear anisotropy on the brane to observable levels, and we use cosmic microwave background anisotropies to place limits on the initial anisotropy induced by these stresses. An initial shear to Hubble distortion of only \sim 10^{-3}\Omega_0h_0^2 at the 5D Planck time would allow the observed large-angle CMB signal to be a relic mainly of KK tidal effects.