On the origin of the Cold Spot
  In a concordant $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model, large-angle
Cosmic Microwave Background (CMB) temperature anisotropy due to linear
perturbations in the local universe is not negligible. We explore a possible
role of an underdense region (void) that may cause an anomalous Cold Spot (CS)
in the CMB sky. Although the observed anomalous cold region with a surrounding
hot ring can be produced by an underdense region surrounded by a massive wall,
a decrement in the CMB temperature in the line-of-sight is suppressed because
of blueshift of CMB photons that pass the wall. Therefore, undercompensated
models give better agreement with the observed data in comparison with
overcompensated or compensated models. We find that it is likely that $\sim$90
per cent of the CMB fluctuation is generated due to an overdense region
surrounded by an underdense region at the last scattering surface, and the
remaining $\sim 10$ per cent is produced due to a single spherical underdense
region with a radius $r\sim 6\times 10^2 h^{-1}$Mpc and a density contrast
$\delta_m\sim -0.009$ ($2 \sigma$) at redshift $z\sim 1$ in the line-of-sight
to the CS. The probability of chance alignment of such two structures is $\sim
0.7$ per cent if the perturbation with an underdense region at $z\sim 1$ is
moderately undercompensated.
