Abstract
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 χ2 was reduced by 9 for three extra parameters. The mean Galactic colatitude and longitude of the modulation, with 68%, 95%, and 99.7% confidence intervals were 56 and 63. The mean percentage change of the variance across the poles of the modulation was 62. Implications of these results and possible generating mechanisms are discussed.
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