Gravitational Magnification of the Cosmic Microwave Background

Some aspects of gravitational lensing by large scale structure (LSS) areinvestigated. We show that lensing causes the damping tail of the cosmicmicrowave background (CMB) power spectrum to fall less rapidly with decreasingangular scale than previously expected. This is due to a transfer of power fromlarger to smaller angular scales which produces a fractional change in powerspectrum that increases rapidly beyond $\ell \sim 2000$. We also find thatlensing produces a nonzero mean magnification of structures on surfaces ofconstant redshift if weighted by area on the sky. This is a result of the factthat light-rays that are evenly distributed on the sky oversample overdenseregions. However this mean magnification has a negligible affect on the CMBpower spectrum. A new expression for the lensed power spectrum is derived andit is found that future precision observations the high-$\ell$ tail of thepower spectrum will need to take into account lensing when determiningcosmological parameters.Comment: to be published in November 1 Astrophysical Journal, 11 pages, two figures, AASTE