Gravitational Lensing Effect on the Two-Point Correlation Function of
  Hot Spots in 21 cm fluctuations
  We investigate the weak gravitational lensing effect on the two-point
correlation function of local maxima (hot spots) in the cosmic 21 cm
fluctuation map. The intrinsic two-point function has a pronounced depression
feature around the angular scale of $\theta \sim 40$ arcmin, which depends on
the observed frequency and corresponds to the scale of the acoustic oscillation
of cosmic plasma before the recombination. It is found that the weak lensing
induces a large w-dependent smoothing at that scale where w is the equation of
state parameter of dark energy and thus provides a useful constraints on the
dark energy property combined with the depression angular scales on the
two-point correlation function.
