Page "Cosmic microwave background radiation" Paragraph 18

With the increasingly precise data provided by WMAP, there have been a number of claims that the CMB suffers from anomalies, such as very large scale anisotropies, anomalous alignments, and non-Gaussian distributions.

The most longstanding of these is the low-l multipole controversy.

Even in the COBE map, it was observed that the quadrupole ( l = 2 spherical harmonic ) has a low amplitude compared to the predictions of the big bang.

Some observers have pointed out that the anisotropies in the WMAP data did not appear to be consistent with the big bang picture.

In particular, the quadrupole and octupole ( l = 3 ) modes appear to have an unexplained alignment with each other and with the ecliptic plane, an alignment sometimes referred to as the axis of evil.

A number of groups have suggested that this could be the signature of new physics at the greatest observable scales ; other groups suspect systematic errors in the data.

Ultimately, due to the foregrounds and the cosmic variance problem, the greatest modes will never be as well measured as the small angular scale modes.

The analyses were performed on two maps that have had the foregrounds removed as best as is possible: the " internal linear combination " map of the WMAP collaboration and a similar map prepared by Max Tegmark and others.

Later analyses have pointed out that these are the modes most susceptible to foreground contamination from synchrotron, dust, and free-free emission, and from experimental uncertainty in the monopole and dipole.

A full Bayesian analysis of the WMAP power spectrum demonstrates that the quadrupole prediction of Lambda-CDM cosmology is consistent with the data at the 10 % level and that the observed octupole is not remarkable.

Carefully accounting for the procedure used to remove the foregrounds from the full sky map further reduces the significance of the alignment by ~ 5 %.