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 -