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Abstract: The cosmic microwave background CMB bispectrum is a well-known probe of thenon-Gaussianity of primordial perturbations. Just as the interveninglarge-scale structure modifies the CMB angular power spectrum through weakgravitational lensing, the CMB primary bispectrum generated at the lastscattering surface is also modified by lensing. We discuss the lensingmodification to the CMB bispectrum and show that lensing leads to an overalldecrease in the amplitude of the primary bispectrum at multipoles of interestbetween 100 and 2000 through additional smoothing introduced by lensing. Sinceweak lensing is not accounted for in current estimators of the primordialnon-Gaussianity parameter, the existing measurements of $f { m NL}$ of thelocal model with WMAP out to $l { m max} \sim 750$ is biased low by about 6%.For a high resolution experiment such as Planck, the lensing modification tothe bispectrum must be properly included when attempting to estimate theprimordial non-Gaussianity or the bias will be at the level of 30%. For Planck,weak lensing increases the minimum detectable value for the non-Gaussianityparameter of the local type $f { m NL}$ to 7 from the previous estimate ofabout 5 without lensing. The minimum detectable value of $f { m NL}$ for acosmic variance limited experiment is also increased from less than 3 to $\sim$5.



Author: Asantha Cooray 1, Devdeep Sarkar 1, Paolo Serra 1 1 UC Irvine

Source: https://arxiv.org/




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