On the detectability of non-trivial topologies

Abstract

We explore the main physical processes which potentially affect the topological signal in the Cosmic Microwave Background (CMB) for a range of toroidal universes. We consider specifically reionisation, the integrated Sachs-Wolfe (ISW) effect, the size of the causal horizon, topological defects and primordial gravitational waves. We use three estimators: the information content, the S/N statistic and the Bayesian evidence. While reionisation has nearly no effect on the estimators, we show that taking into account the ISW strongly decreases our ability to detect the topological signal. We also study the impact of varying the relevant cosmological parameters within the 2 sigma ranges allowed by present data. We find that only Omega_Lambda, which influences both ISW and the size of the causal horizon, significantly alters the detection for all three estimators considered here.

11 pages, 9 figures

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• Constraining the topology of the Universe using the polarised CMB maps
• Cosmic microwave anisotropies in an inhomogeneous compact flat universe
• What can the detection of a single pair of circles-in-the-sky tell us about the geometry and topology of the Universe ?
• Cosmic topology. Part IIIa. Microwave background parity violation without parity-violating microphysics
• A spatial-correlation analysis of the cubic 3-torus topology based on the Planck 2013 data