Anomalous large-angle cosmic microwave background (CMB) anisotropies motivate further searches for cosmic topology beyond just our curiosity about this fundamental property of the Universe. Observational searches, using the CMB, have so far considered only a small subset of testable topologies, and current limits on the topology scale are much weaker than generally understood. For generic topologies of spatially flat spacetimes, off-diagonal correlations between microwave background harmonic coefficients over a wide range of scales encode significant topological information. In Fourier space, i.e., for future galaxy and 21cm surveys such as ESA’s Euclid mission and the SKA Observatory, these correlations may hold true even if the topology scale substantially exceeds the diameter of the observable Universe. I describe an ambitious program to exhaustively search for cosmic topology in current and future cosmological data.
Stefano Anselmi, Nicola Bartolo, Daniele Bertacca, Stefano Dusini, Michele Liguori, Sabino Matarrese, Alvise Raccanelli, Alessandro Renzi, Angelo Ricciardone, Chiara Sirignano, Luca Stanco
