sensitivity of WMAP are not ideal for detection of the typical SZ effect. However, if a large number of SZ clusters contribute to the CMB map, their imprint can be statistically measurable. Recently, the positive cross-correlation between the X-ray clusters and the WMAP map has been detected. Hernández-Monteagudo & Rubiño-Martín (2003) claim their detection at $2\sigma$ – $5\sigma$ level, which corresponds to the amplitude of typically 20 – 30 $\mu$K in the WMAP map (see also Boughn & Crittenden 2003; Fosalba & Gaztañaga 2003; Fosalba et al. 2003; Myers et al. 2003).

Third, the non-Gaussian signatures may be caused by the inhomogeneous photon damping during the reionisation at the earlier epoch. Reionisation damping depends on the total optical depth $\tau$ and the angular scale subtended by the horizon at the last scattering surface defined during the reionisation epoch. The primary CMB anisotropy $\Delta T$ is damped to $\Delta T e^{-\tau}$ by the Thompson scattering with electrons, and the damping contribution to the anisotropy depends on scales. The characteristic damping scale $\ell_r$ is given by $\ell_r = (1+z_r)^{1/2} (1+0.084\ln\Omega_0)-1$ (Hu & White 1997; Griffiths, Barbosa, & Liddle 1999), where $z_r$ denotes the reionisation epoch. For $z_r \approx 20$ and $\Omega_0 \approx 