Kaluza–Klein anisotropy in the CMB

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 ∼10−3Ω0h02 at the 5D Planck time would allow the observed large-angle CMB signal to be a relic mainly of KK tidal effects.