“School of Astronomy”
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| Paper IPM / Astronomy / 14277 |
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Full-sky maps of the cosmic microwave background temperature reveal a 7% asymmetry of uctuation power between two halves of the sky. A common phenomenological model for this asymmetry is an overall dipole modulation of statistically isotropic uctuations, which produces particular o-diagonal correlations between multipole coecients. We compute these correlations and constructcorresponding estimators for the amplitude and direction of the dipole modulation. Applying these
estimators to various cut-sky temperature maps from Planck and WMAP data shows consistency with a dipole modulation, diering from a null signal at 2.5
, with an amplitude and direction con-
sistent with previous ts based on the temperature uctuation power. The signal is scale dependent,
with a statistically signicant amplitude at angular scales larger than 2 degrees. Future measure-
ments of microwave background polarization and gravitational lensing can increase the signicance
of the signal. If the signal is not a statistical uke in an isotropic Universe, it requires new physics
beyond the standard model of cosmology.
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