Gravitational lensing of cosmic microwave background anisotropies and cosmological parameter estimation

Gravitational lensing, caused by matter perturbations along the line of sig ht to the last scattering surface, can modify the shape of the cosmic micro wave background (CMB) anisotropy power spectrum. We discuss the detectabili ty of lensing distortions to the temperature, polarization and temperature- polarization cross-correlation power spectra, and we analyse how lensing mi ght affect the estimation of cosmological parameters. For cold dark matter like models with present-day matter power spectra normalized to match the a bundances of rich clusters of galaxies, gravitational lensing causes detect able distortions to cosmic variance-limited CMB experiments sampling high m ultipoles ( l greater than or similar to 1000). Gravitational lensing of th e CMB, although a small effect, allows independent determinations of the cu rvature of the Universe and the cosmological constant, i.e., breaking the s o-called geometrical degeneracy in CMB parameter estimation discussed by Bo nd, Efstathiou & Tegmark and Zaldarriaga, Spergel & Seljak. Gravitational l ensing of the CMB temperature and polarization patterns should be detectabl e by the Planck Surveyor satellite, leading to useful independent constrain ts on the cosmological constant and spatial curvature.