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Planck 2015 results. XVIII. Background geometry and topology of the Universe

Abstract : Full-sky CMB maps from the 2015 Planck release allow us to detect departures from global isotropy on the largest scales. We present the first searches using CMB polarization for correlations induced by a non-trivial topology with a fundamental domain intersecting, or nearly intersecting, the last scattering surface (at comoving distance χrec). We specialize to flat spaces with toroidal and slab topologies, finding that explicit searches for the latter are sensitive to other topologies with antipodal symmetry. These searches yield no detection of a compact topology at a scale below the diameter of the last scattering surface. The limits on the radius Ri of the largest sphere inscribed in the topological domain (at log-likelihood-ratio ΔlnL>−5 relative to a simply-connected flat Planck best-fit model) are Ri>0.97χrec for the cubic torus and Ri>0.56χrec for the slab. The limit for the cubic torus from the matched-circles search is numerically equivalent, Ri>0.97χrec (99% CL) from polarisation data alone. We also perform a Bayesian search for a Bianchi VIIh geometry. In the non-physical setting where the Bianchi cosmology is decoupled from the standard cosmology, Planck temperature data favour the inclusion of a Bianchi component. However, the cosmological parameters generating this pattern are in strong disagreement with those found from CMB anisotropy data alone. Fitting the induced polarization pattern for this model to Planck data requires an amplitude of −0.1±0.04 compared to +1 if the model were to be correct. In the physical setting where the Bianchi parameters are fit simultaneously with the standard cosmological parameters, we find no evidence for a Bianchi VIIh cosmology and constrain the vorticity of such models to (ω/H)0<7.6×10−10 (95% CL). [Abridged]
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Contributor : Sabine Starita <>
Submitted on : Tuesday, February 10, 2015 - 4:52:06 PM
Last modification on : Wednesday, September 16, 2020 - 4:28:11 PM

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.A.R. Ade, A. Benoit, F. Couchot, S. Henrot-Versillé, A. Mangilli, et al.. Planck 2015 results. XVIII. Background geometry and topology of the Universe. Astronomy and Astrophysics - A&A, EDP Sciences, 2016, 594, pp.A18. ⟨10.1051/0004-6361/201525829⟩. ⟨in2p3-01115263⟩



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