Gravitational lensing, caused by matter perturbations along the line-of-sight
to the last scattering surface, can modify the shape of the cosmic microwave
background (CMB) anisotropy power spectrum. We discuss the detectability of
lensing distortions to the temperature, polarisation and
temperature-polarisation cross-correlation power spectra and we analyse how
lensing might affect the estimation of cosmological parameters. For cold dark
matter-like models with present-day matter power spectra normalised to match
the abundances of rich clusters of galaxies, gravitational lensing causes
detectable distortions to cosmic variance limited CMB experiments sampling high
multipoles (l > 1000). Gravitational lensing of the CMB, although a small
effect, allows independent determinations of the curvature of the universe and
the cosmological constant, i.e. breaking the so-called geometrical degeneracy
in CMB parameter estimation discussed by Bond, Efstathiou and Tegmark (1997)
and Zaldarriaga, Spergel and Seljak (1997). Gravitational lensing of the CMB
temperature and polarisation patterns should be detectable by the Planck
Surveyor satellite leading to useful independent constraints on the
cosmological constant and spatial curvature.Comment: 14 pages, 8 figures, uses mn.sty, improved analysis conclusions
unchanged, matches the version accepted for the publicatio