The Cold Spot as a Large Void: Rees-Sciama effect on CMB Power Spectrum and Bispectrum

Understand

The detection of a "Cold Spot" in the CMB sky could be explained by the presence of an anomalously large spherical underdense region (with radius of a few hundreds Mpc/h) located between us and the Last Scattering Surface.

• Modeling such an underdensity with an LTB metric, we investigate whether it could produce significant signals on the CMB power spectrum and bispectrum, via the Rees-Sciama effect.
• We find that this leads to a bump on the power spectrum, that corresponds to an O(5%-25%) correction at multipoles 5 < l < 50; in the cosmological fits, this would modify the \chi^2 by an amount of order unity.
• We also find that the signal should be visible in the bispectrum coefficients with a signal-to-noise S/N ~ O (1-10), localized at 10 < l < 40.