The CMB bispectrum in the squeezed limit
- Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34151, Trieste (Italy)
- Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX (United Kingdom)
- CEA, Institut de Physique Théorique, 91191 Gif-sur-Yvette cédex (France)
The CMB bispectrum generated by second-order effects at recombination can be calculated analytically when one of the three modes has a wavelength much longer than the other two and is outside the horizon at recombination. This was pointed out in [1] and here we correct their results. We derive a simple formula for the bispectrum, f{sub NL}{sup loc} = −(1/6+cos 2θ)⋅(1−1/2⋅dln (l{sub S}{sup 2}C{sub S})/dln l{sub S}), where C{sub S} is the short scale spectrum and θ the relative orientation between the long and the short modes. This formula is exact and takes into account all effects at recombination, including recombination-lensing, but neglects all late-time effects such as ISW-lensing. The induced bispectrum in the squeezed limit is small and will negligibly contaminate the Planck search for a local primordial signal: this will be biased only by f{sub NL}{sup loc} ≈ −0.4. The above analytic formula includes the primordial non-Gaussianity of any single-field model. It also represents a consistency check for second-order Boltzmann codes: we find substantial agreement with the current version of the CMBquick code.
- OSTI ID:
- 22280265
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2011, Issue 11; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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