CMB Anisotropy in Compact Hyperbolic Universes

Abstract

Measurements of CMB anisotropy are ideal experiments for discovering the non-trivial global topology of the universe. To evaluate the CMB anisotropy in multiply-connected compact cosmological models, one needs to compute eigenmodes of the Laplace-Beltrami operator. We numerically obtain the eigenmodes on a compact 3-hyperbolic space cataloged as $m003(-2,3)$ in SnapPea (computer program by Jeff Weeks) using the direct boundary element method, which enables one to simulate the CMB in multiply-connected compact models with high precision. The angular power spectra $C_{l}$'s ($2 \leq l\leq18$) are calculated using computed eigenmodes for $5.4\leqk<10$ and Gaussian random approximation for the expansion coefficients for $10\leqk<20$. Assuming that the initial power spectrum is the Harrison-Zeldovich spectrum, the computed $C_l$'s are consistent with the COBE data for $0.1 \leqΩ_o \leq 0.6$. In low $Ω_o$ models, the large-angular fluctuations can be produced at periods after the last scattering as the curvature perturbations decay in the curvature dominant era.