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What if Planck’s Universe isn’t flat?

2013; American Physical Society; Volume: 87; Issue: 8 Linguagem: Inglês

10.1103/physrevd.87.081301

1550-7998

Philip Bull, Marc Kamionkowski,

Galaxies: Formation, Evolution, Phenomena

Inflationary theory predicts that the observable Universe should be very close to flat, with a spatial-curvature parameter $|{\ensuremath{\Omega}}_{K}|\ensuremath{\lesssim}{10}^{\ensuremath{-}4}$. The WMAP satellite currently constrains $|{\ensuremath{\Omega}}_{K}|\ensuremath{\lesssim}0.01$, and the Planck satellite will be sensitive to values near ${10}^{\ensuremath{-}3}$. Suppose that Planck were to find ${\ensuremath{\Omega}}_{K}\ensuremath{\ne}0$ at this level. Would this necessarily be a serious problem for inflation? We argue that an apparent departure from flatness could be due either to a local (wavelength comparable to the observable horizon) inhomogeneity, or a truly superhorizon departure from flatness. If there is a local inhomogeneity, then secondary cosmic microwave background (CMB) anisotropies distort the CMB frequency spectrum at a level potentially detectable by a next-generation experiment. We discuss how these spectral distortions would complement constraints on the Grishchuk-Zel'dovich effect from the low-$\ensuremath{\ell}$ CMB power spectrum in discovering the source of the departure from flatness.