[0709.0886] Compact Universe Signature in the Cosmic Microwave Background

Authors:  V. G. Gurzadyan, A. Kashin, C. L. Bianco, H. Khachatryan, G. Yegorian
Abstract:  In the Cosmic Microwave Background (CMB) temperature maps obtained at the Wilkinson Microwave Anisotropy Probe (WMAP) three year measurements, we have found an anomaly in the distribution of the excursion sets (anisotropy spots). The anomaly is centered at the antipodes with galactic coordinates l=92^\circ, b=30^\circ and l=275^\circ, b=-31^\circ. The scale and the substructure, i.e. 30^\circ-radius rings and voids in the distribution of the excursion sets around the antipodes, reveal features of mirroring which cannot be explained either via global (integrated Sachs-Wolf effect) or local inhomogeneities of matter. The anomaly is also not close to the apex of the CMB dipole. This mirroring effect can be the first empirical signature of a Universe with compact topology, potentially of either curvature.
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Hans Kristian Eriksen
Posts: 60
Joined: September 25 2004
Affiliation: ITA, University of Oslo

[0709.0886] Compact Universe Signature in the Cosmic Microw

Post by Hans Kristian Eriksen » September 07 2007

This paper appeared on astro-ph today, with some fairly aggressive claims about detection of compact topology. Essentially, they compute the excursion sets (that is, regions with T > T_0), and plot connected regions with more than, say, 200 pixels. At least, that's what I think they do.

Then they find that lots of connected regions start popping up on two opposing hemispheres, once they start increasing T_0. Their axis is found to be centered on l=92, b=30 -- which, unfortunately, is very close to the ecliptic pole (l = 96, b=30), which also happens to be the symmetry axis of WMAP's scanning strategy.

A more natural explanation than a closed universe (to me, at least), is therefore that they are starting to see the CMB through the instrumental noise as they adjust T_0. This happens in the ecliptic poles earlier than in the ecliptic plane, because the noise is lower there. So a first good test for this analysis, I think, is to do the same with WMAP-like simulations, taking into account the WMAP hit count pattern..

Carlo Contaldi
Posts: 16
Joined: November 19 2004
Affiliation: Imperial College

[arXiv:0709.0886] Compact Universe Signature in the Cosmic M

Post by Carlo Contaldi » September 07 2007

exactly...you simply shouldn't treat any real CMB observation as a Gaussian random field with uniform variance, if you do you'll find all kinds of anomalies. Claims like this have little meaning without a proper comparison to simulated observations particularly when you find a signal which is correlated with the scan strategy. It's the cosmological equivalent of reporting a lab measurement without stating any errors.

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