Evidence of primordial non-Gaussianity (fNL) in the Wilkinson Microwave Anisotropy Probe 3-year data at 2.8σ

We present evidence for primordial non-Gaussianity of the local type (f(NL)) in the temperature anisotropy of the cosmic microwave background. Analyzing the bispectrum of the Wilkinson Microwave Anisotropy Probe 3-year data up to l(max) = 750 we find 27 < f(NL) < 147 (95% C.L.). This amounts to a rejection of f(NL) = 0 at 2.8 sigma, disfavoring canonical single-field slow-roll inflation. The signal is robust to variations in l(max), frequency and masks. No known foreground, instrument systematic, or secondary anisotropy explains it. We explore the impact of several analysis choices on the quoted significance and find 2.5 sigma to be conservative.