Broken Isotropy from a Linear Modulation of the Primordial Perturbations

A linear modulation of the primordial perturbations is proposed as an explanation for the observed asymmetry between the northern and southern hemispheres of the Wilkinson Microwave Anisotropy Probe (WMAP) data. A cut sky, reduced resolution third year "Internal Linear Combination" (ILC) map was used to estimate the modulation parameters. A foreground template and a modulated plus unmodulated monopole and dipole were projected out of the likelihood. The effective chi squared is reduced by nine for three extra parameters. The mean Galactic colatitude and longitude, of the modulation, with 68%, 95% an 99. 7% confidence intervals was 56^+17 +36 +65-₁₇ -₃₅ -₅₁ and 63^+28 +59 +105-₂₆ -₅₈ -₂₁₃. The mean percentage change of the variance, across the pole's of the modulation, was 62^+18 +35 +57-₁₈ -₃₅ -₄₇. Implications of these results and possible generating mechanisms are discussed.