TY - JOUR

T1 - Sachs-Wolfe at second order

T2 - The CMB bispectrum on large angular scales

AU - Boubekeur, Lotfi

AU - Creminelli, Paolo

AU - D'Amico, Guido

AU - Norẽa, Jorge

AU - Vernizzi, Filippo

PY - 2009

Y1 - 2009

N2 - We calculate the Cosmic Microwave Background anisotropy bispectrum on large angular scales in the absence of primordial non-Gaussianities, assuming exact matter dominance and extending at second order the classic Sachs-Wolfe result δT/T = Φ/3. The calculation is done in Poisson gauge. Besides intrinsic contributions calculated at last scattering, one must consider integrated effects. These are associated to lensing, and to the time dependence of the potentials (Rees-Sciama) and of the vector and tensor components of the metric generated at second order. The bispectrum is explicitly computed in the flat-sky approximation. It scales as l -4 in the scale invariant limit and the shape dependence of its various contributions is represented in 3d plots. Although all the contributions to the bispectrum are parametrically of the same order, the full bispectrum is dominated by lensing. In the squeezed limit it corresponds to f NL local = -1/6-cos(2θ), where θ is the angle between the short and the long modes; the angle dependent contribution comes from lensing. In the equilateral limit it corresponds to f NL equil 3.13.

AB - We calculate the Cosmic Microwave Background anisotropy bispectrum on large angular scales in the absence of primordial non-Gaussianities, assuming exact matter dominance and extending at second order the classic Sachs-Wolfe result δT/T = Φ/3. The calculation is done in Poisson gauge. Besides intrinsic contributions calculated at last scattering, one must consider integrated effects. These are associated to lensing, and to the time dependence of the potentials (Rees-Sciama) and of the vector and tensor components of the metric generated at second order. The bispectrum is explicitly computed in the flat-sky approximation. It scales as l -4 in the scale invariant limit and the shape dependence of its various contributions is represented in 3d plots. Although all the contributions to the bispectrum are parametrically of the same order, the full bispectrum is dominated by lensing. In the squeezed limit it corresponds to f NL local = -1/6-cos(2θ), where θ is the angle between the short and the long modes; the angle dependent contribution comes from lensing. In the equilateral limit it corresponds to f NL equil 3.13.

KW - CMBR theory

KW - Cosmological perturbation theory

KW - Non-gaussianity

UR - http://www.scopus.com/inward/record.url?scp=70350641711&partnerID=8YFLogxK

U2 - 10.1088/1475-7516/2009/08/029

DO - 10.1088/1475-7516/2009/08/029

M3 - Article

AN - SCOPUS:70350641711

VL - 2009

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 8

M1 - 029

ER -