Significance of the largest scale CMB fluctuations in WMAP

Abstract

-still no referee report. abstract We investigate anomalies reported in the Cosmic Microwave Background maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite on very large angular scales and discuss possible interpretations. Three independent anomalies involve the quadrupole and octopole: 1) The cosmic quadrupole on its own is anomalous at the 1-in-20 level by being low (the cut-sky quadrupole measured by the WMAP team is more strikingly low, apparently due to a coincidence in the orientation of our Galaxy of no cosmological significance); 2) The cosmic octopole on its own is anomalous at the 1-in-20 level by being very planar;3) The alignment between the quadrupole and octopole is anomalous at the 1-in-60 level. Although the a priori chance of all three occurring is 1 in 24000, the multitude of alternative anomalies one could have looked for dilutes the significance of such a posteriori statistics. The simplest small universe model where the universe has toroidal topology with one small dimension of order half the horizon scale, in the direction towards Virgo, could explain the three items above. However, we rule this model out using two topological tests: the S-statistic and the matched circle test. In particular, our results rule out the recently proposed dodecahedron model of Luminet, Weeks, Riazuelo, Lehoucq & Uzan.

Three-form cosmology

“…Two-forms appear also in the framework of the asymmetric gravity [16] as the antisymmetric contribution to the metric, and have been considered in cosmology [17]. Forms, being intrinsically anisotropic, could be relevant for a dynamical origin of the four large dimensions [18], modelling Lorentz violation [19] or the observed CMB anomalies [20]. Form-driven inflation was suggested earlier this year [21,22].…”

Could dark energy be vector-like?

“…At present the effect is still small, since the relative amplitude has increased at most by a factor of order one. In fact, it is tempting to speculate whether some of the anomalies observed in the CMB radiation [23], specially in the quadrupole and octopole (see however [44]) and the related hints of statistical anisotropy [22], might be due to such an instability, which sets in once the universe starts to accelerate and mostly affects large scales.…”

“…Eventually, it might be even necessary to introduce fields that explicitly violate rotational symmetry, as there appear to be hints of (statistical) anisotropy in the CMB fluctuations [22]. Along these lines, I speculate below that a triad could provide a link between cosmic acceleration and some of the anomalies observed in the CMB radiation [22,23].…”

“…Along these lines, I speculate below that a triad could provide a link between cosmic acceleration and some of the anomalies observed in the CMB radiation [22,23].…”

The Axis of Evil - A Polarization Perspective

“…However, in recent years, there have been claims of anomalies detected in the CMB temperature map with considerable significance, which seem to break statistical isotropy of the temperature fluctuations and thus to question the cosmological principle. Among these anomalies, there is a strong alignment between the preferred axes of the quadrupole and the octopole, which is commonly referred to as the axis of evil [3,1,11,16,15]. The claims of the existence of a preferred direction in the CMB temperature map have led to a discussion about whether this is simply due to a chance fluctuation in the CMB temperature map, if it can be blamed on local structures or on systematics in the measurement, or whether it is actually due to a preferred direction intrinsic to the geometry of the primordial Universe [4,12,17,8,13,18,10].…”