Measuring dark matter power spectrum from cosmic microwave background

We propose a method to extract the projected power spectrum of density pert urbations from the distortions in the cosmic microwave background (CMB). Th e distortions are imprinted onto the CMB by the gravitational lensing effec t and can be extracted using a combination of products of CMB derivatives. Future CMB experiments such as the Planck satellite experiment will be able to extract the power spectrum with high statistical significance over 2 or ders of magnitude in angle. The method proposed here directly traces dark m atter in the linear regime to higher redshift (up to z similar to 1100) and larger scale (a few Gpc) than any other currently known method. [S0031-900 7(99)08558-0].