Gravitational lensing and finite beam-width effect on cosmic microwave anisotropies

The temperature anisotropies of cosmic microwave background under the influence of gravitational lenses are investigated taking into account the smearing effect due to a finite beam-width of an observational apparatus. In contrast to the zero beam-width case, in which the anisotropies on small angular scales are enhanced by the lens effect, a finite beam-width may smear out the so-enhanced anisotropies and hence can lead to a suppression of the small angular anisotropies. Using a simple model of the temperature fluctuation spectrum at the decoupling epoch, this possibility is examined over various model parameters. It is found that a strong suppression of the anisotropies occurs only in the case when the beam-width is comparable or greater than the intrinsic coherence angle θc of the temperature anisotropy and the characteristic deflection angle by gravitational lenses is much larger than θc. (author)