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Sep13-06, 06:32 PM
Sci Advisor
PF Gold
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P: 23,266
Was the universe open or closed before inflation?
Eduard Masso, Subhendra Mohanty, Gabriel Zsembinszki
5 pages, 3 figures

"If the spatial curvature of the universe at the beginning of inflation is negative, there is an enhancement of the temperature anisotropy of the Cosmic Background Radiation at large angles. On the other hand if at the start of inflation the universe was closed with curvature there will be a suppression of temperature anisotropy at the scale of the present horizon. The observation of a low quadrupole anisotropy by WMAP suggests that the universe was closed with [itex](\Omega-1)[/itex] of order unity at the time when the perturbation scales of the size of our present horizon were exiting the inflationary horizon."

From the analyis of the three year WMAP data [2] it is concluded that a power power spectrum with an exponential cut-off at [itex]k_c/a_0 = 3 \times 10^{-4}Mpc^{-1} [/itex] gives a better chi-square fit for the temperature anisotropy angular spectrum than the nearly scale invariant spectrum predicted by an generic slow roll inflation. If the universe was closed at the time of inflation then there is a natural cut-off of [itex]k^2 = K/a^2_i [/itex].
Running the cmbflat programme of CMBFAST [3] after modifying the primordial power spectrum of scalars by including the extra factor in the square brackets of (43), with [itex]\Omega_0 = 1 [/itex]
and other parameters as given by the central values of the λ CDM model, [2], we find that a good fit for the low-multipole TT anisotropy is obtained with [itex]|K|/(a_iH_{\lambda})^2 \sim 1 [/itex] as shown in Fig.1. Therefore a natural explanation of the low cmb power at low l is that the universe was closed at the start of inflation with [itex]\Omega - 1 \sim O(1) [/itex].