title: Gauge-invariant temperature anisotropies and primordial non-Gaussianity.
abstract: We provide the gauge-invariant expression for large-scale cosmic microwave background temperature fluctuations at second-order perturbation theory. This enables us to define unambiguously the nonlinearity parameter f(NL), which is used by experimental collaborations to pin down the level of non-Gaussianity in the temperature fluctuations. Furthermore, it contains a primordial term encoding all the information about the non-Gaussianity generated at primordial epochs and about the mechanism which gave rise to cosmological perturbations, thus neatly disentangling the primordial contribution to non-Gaussianity from the one caused by the postinflationary evolution.
authors.affiliation: Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, United Kingdom.
authors.forename: Nicola
authors.initials: N
authors.lastname: Bartolo
authors.forename: Sabino
authors.initials: S
authors.lastname: Matarrese
authors.forename: Antonio
authors.initials: A
authors.lastname: Riotto