V. G. Gurzadyan and A. A. Kocharyan, Astronomy & Astrophysics (Letters)493, L61 (2009); for a free pdf version see

http://www.aanda.org/articles/aa/pdf/2009/03/aa11317-08.pdf

The voids - underdense regions in the large scale matter distribution in the Universe - are currently among key issues in cosmology and are studied based mainly on galaxy surveys. The voids in the vicinity of the Local Group of galaxies are studied in more details, while their properties at higher redshifts remain unclear. Existence of larger voids has been hypothesized but also remains uncertain.

This is among the first papers introducing a signature of voids in the Cosmic Microwave Background (CMB). Namely, the degree of randomness in the CMB maps was shown to be indicative of the hyperbolic effect of voids on the propagation of the photon beams. In terms of an introduced porosity parameter, a criterion was obtained for a hyperbolicity due to domination of voids in the line-of-sight direction. That criterion was shown to be supported by the parameters of 30 Mpc scale voids revealed by the galactic redshift surveys. The importance of the geometrical effect of the voids is also due to their role in the temperature independent ellipticity of the excursion sets measured for BOOMERanG and WMAP data, as well as in the nature of dark energy.

The data of PLANCK mission enable further studies of voids using the CMB data, along with those of galaxy surveys.