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Implications about the large scale properties of the universe from the cosmic microwave background


We analyze the large scale properties of the universe using the seven-year WMAP temperature data. We investigate the global topology of the universe, as well as semiclassical fluctuations of primordial perturbations on large scales. We study the possibility that the universe is flat, but with one or more space directions compactified. We constrain the size of the compact dimension to be L/L₀ = 1.27, 0.97, 0.57 at 95% confidence for the case of three, two and one compactified dimension, respectively, where L₀ = 14.4 Gpc is the distance to the last scattering surface. We find a statistically significant signal for a compact universe, and the best- fit spacetime is a universe with two compact directions of size L/L₀ = 1.9, with the non-compact direction pointing in a direction close to the velocity of the Local Group. We consider two possible semiclassical modifications of the primordial power spectrum. For the amplitude of a fluctuation in one Fourier mode we find the 95% bound of a₀ = 6.45 x 10⁻⁴. For a semiclassical gaussian fluctuation in space the 95% confidence region for the amplitude is - 5.16 x 10⁻² = a₀ = 5.07 x 10⁻². We show that the scenarios we consider are not responsible for the previously suggested possible special direction in space, the so- called "axis of evil"

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