IS LENSING OF POINT SOURCES A PROBLEM FOR FUTURE CMB EXPERIMENTS

Weak gravitational lensing from large-scale structure enhances and red uces the fluxes from extragalactic point sources with an rms amplitude of order 15 per cent. In cosmic microwave background (CMB) experiment s, sources exceeding some flux threshold phi(c) are removed, which mea ns that lensing will modulate the brightness map of the remaining unre solved sources. Because this mean brightness is of order 100 mu K at 3 0 GHz for a reasonable flux cut, one might be concerned that this modu lation could cause substantial problems for future CMB experiments. We present a detailed calculation of this effect and, fortunately, find that its power spectrum is always smaller than the normal point source power spectrum. Thus although this effect should be taken into accoun t when analysing future high-precision CMB measurements, it will not s ubstantially reduce the accuracy with which cosmological parameters ca n be measured.