  We present quantitative investigations of the weak lensing effect on the
two-point correlation functions of local maxima (hotspots),
  $\xipk(\theta)$, in the cosmic microwave background (CMB) maps. The lensing
effect depends on the projected mass fluctuations between today and the
redshift $z_{\rm rec}\approx1100$. If adopting the Gaussian assumption for the
primordial temperature fluctuations field, the peak statistics can provide an
additional information about the intrinsic distribution of hotspots that those
pairs have some characteristic separation angles. The weak lensing then
redistributes hotspots in the observed CMB maps from the intrinsic distribution
and consequently imprints non-Gaussian signatures onto $\xipk(\theta)$.
Especially, since the intrinsic $\xipk(\theta)$ has a pronounced depression
feature around the angular scale of $\theta\approx 70'$ for a flat universe,
the weak lensing induces a large smoothing at the scale. We show that the
lensing signature therefore has an advantage to effectively probe mass
fluctuations with large wavelength modes around $\lambda\approx 50 h^{-1}{\rm
Mpc}$. To reveal the detectability, we performed numerical experiments with
specifications of {\em MAP} and {\em Planck Surveyor} including the
instrumental effects of beam smoothing and detector noise. It is then found
that our method can successfully provide constraints on amplitude of the mass
fluctuations and cosmological parameters in a flat universe with and without
cosmological constant, provided that we use maps with 65% sky coverage expected
from Planck.
