Quasilinear evolution of compensated cosmological perturbations: The nonlinear sigma model

Non-Gaussian signatures from the postinflationary early universe

We consider contributions to non-Gaussianity of the cosmic microwave background (CMB) from remnants of phase transitions in the very early Universe. Such signatures can optimistically be used to discover evidence of new particle physics through cosmological observations. More conservatively they may provide an obstacle to extracting information about the non-Gaussian nature of primordial density fluctuations from any detection in the CMB. We study this explicitly by computing the bispectrum from global textures, which occur in a wide class of particle physics models.

Estimate of the cosmological bispectrum from the MAXIMA-1 cosmic microwave background map

We use the measurement of the cosmic microwave background taken during the MAXIMA-1 flight to estimate the bispectrum of cosmological perturbations. We propose an estimator for the bispectrum that is appropriate in the flat sky approximation, apply it to the MAXIMA-1 data, and evaluate errors using bootstrap methods. We compare the estimated value with what would be expected if the sky signal were Gaussian and find that it is indeed consistent, with a chi(2) per degree of freedom of approximately unity. This measurement places constraints on models of inflation.