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Non-Gaussianity and the CMB bispectrum: Confusion between primordial and lensing-Rees-Sciama contribution?
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We revisit the predictions for the expected cosmic microwave background bispectrum signal from the cross-correlation of the primary-lensing-Rees-Sciama signal; we point out that it can be a significant contaminant to the bispectrum signal from primordial non-Gaussianity of the local type. This non-Gaussianity, usually parametrized by the non-Gaussian parameter f N L , arises, for example, in multifield inflation. In particular both signals are frequency-independent, and are maximized for nearly squeezed configurations. While their detailed scale-dependence and harmonic imprints are different for generic bispectrum shapes, we show that, if not included in the modeling, the primary-lensing-Rees-Sciama contribution yields an effective f N L of 10 when using a bispectrum estimator optimized for local non-Gaussianity. Considering that expected 1 − σ errors on f N L are < 10 from forthcoming experiments, we conclude that the contribution from this signal must be included in future constraints on f N L from the cosmic microwave background bispectrum.
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MANGILLI, Anna and VERDE, Licia. Non-Gaussianity and the CMB bispectrum: Confusion between primordial and lensing-Rees-Sciama contribution?. Physical Review D. 2009. Vol. 80, num. 12, pags. 123007. ISSN 1550-7998. [consulted: 10 of June of 2026]. Available at: https://hdl.handle.net/2445/131761