paper

Non-Gaussian Correlations Outside the Horizon

arXiv:0808.2909 · doi:10.1103/PhysRevD.78.123521

Abstract

It is shown that under essentially all conditions, the non-linear classical equations governing gravitation and matter in cosmology have a solution in which far outside the horizon in a suitable gauge the reduced spatial metric (the spatial metric divided by the square of the Robertson--Walker scale factor ) is time-independent, though with an arbitrary dependence on co-moving coordinates, and all perturbations to the other metric components and to all matter variables vanish, to leading order in . The corrections are of order , and are explicitly given for the reduced metric in a multifield model with a general potential. Further, this is the solution that describes the metric and matter produced by single-field inflation. These results justify the use of observed non-Gaussian correlations (or their absence) as a test of theories of single-field inflation, despite our ignorance of the constituents of the universe while fluctuations are outside the horizon after inflation, as long as graphs with loops can be neglected.

25 pages. This version clarifies the scale transformation used in Section II and the gauge transformation used in Section III, and corrects some typos, including new typos introduced in version 2

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