Three-point temperature anisotropies in WMAP:: Limits on CMB non-Gaussianities and nonlinearities -: art. no. 021302

We present a study of the three-point angular correlation function w(3) = (delta(1)delta(2)delta(3)) of (adimensional) temperature anisotropies measured by the Wilkinson Microwave Anisotropy Probe. The results can be normalized to the two-point function w(2) = (delta(1)delta(2)) in terms of the hierarchical q(3)similar tow(3)/w(2)(2) or dimensionless d(3)similar tow(3)/w(2)(3/2) amplitudes. Strongly non-Gaussian models are generically expected to show d(3)>1 or q(3)>10(3)d(3). Unfortunately, this is comparable to the cosmic variance on large angular scales. For Gaussian primordial models, q(3) gives a direct measure of the nonlinear corrections to temperature anisotropies in the sky: delta=delta(L)+f(NLT)(delta(L)(2) -(delta(L)(2))) with f(NLT)=q(3)/2 for the leading order term in w(2)(2). We find good agreement with the Gaussian hypothesis d(3)similar to0 within the cosmic variance of the simulations of the cold dark matter model with a cosmological constant (ACDM) (with or without a low quadrupole). The strongest constraints on q(3) come from scales smaller than 1degrees. We find q(3)=19 +/- 141 for (pseudo) collapsed configurations and an average of q(3) = 336 +/- 218 for noncollapsed triangles. The corresponding nonlinear coupling parameter f(NL) for curvature perturbations Phi, in the Sachs-Wolfe regime is f(NL)(SW) = q(3)/6, while on degree scales, the extra power in acoustic oscillations produces f(NL)similar toq(3)/30 in the A CDM. Errors are dominated by cosmic variance, but for the first time they begin to be small enough to constrain the leading order nonlinear effects with a coupling of the order of unity.