2018/09/16 by Bernui, Armando, Novaes, Camila P., Pereira, Thiago S. +1
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences
paper · doi:10.48550/arxiv.1809.05924
To date, no compelling evidence has been found that the universe has non-trivial spatial topology. Meanwhile, anomalies in the observed CMB temperature map, such as the lack of correlations at large angular separations, remain observationally robust. We show that if our universe is flat and has one compact dimension of appropriate size (slab topology), this would suppress large-angle temperature correlations while maintaining a low-ℓ angular power spectrum consistent with observations. The optimal length appears to be 1.4 times the conformal radius of the CMB's last scattering surface (χrec). We construct the probability distribution function of the statistic S1/2 using simulated Sachs-Wolf-only skies for each of several values of Lz/χrec. For Lz≃1.4χrec the p-value of four standard masked Planck maps is p≃0.15, compared to p\lesssim0.003 for the conventional topologically trivial space. The mean angular power spectrum ⟨ Cℓ ⟩ of the Lz=1.4χrec slab space matches the observed power spectrum at 2≤ℓ\lesssim6 -- including a substantially suppressed quadrupole C2, a slightly suppressed octopole C3, and unsuppressed higher multipoles. It does not predict other low-ℓ CMB anomalies, and does not take account of normally sub-dominant Integrated Sachs Wolfe contributions. An Lz=1.4χrec slab topology is consistent with published limits from the Planck maps (Lz\gtrsim1.12χrec). It is within the 95% confidence range 1.2≤ Lz/χrec≤2.1 inferred using the covariance-matrix of temperature fluctuations. However, it violates published circles-in-the-sky limits from WMAP and related unpublished limits from Planck (Lz/χrec\gtrsim1.9). We remark on the possibility to satisfy these limits, and "postdict" other large-angle anomalies, with closely related topologies.