Generating Scale-Invariant Perturbations from Rapidly-Evolving Equation of State
arXiv:1101.3548 · doi:10.1103/PhysRevD.83.123502
Abstract
Recently, we introduced an ekpyrotic model based on a single, canonical scalar field that generates nearly scale invariant curvature fluctuations through a purely "adiabatic mechanism" in which the background evolution is a dynamical attractor. Despite the starkly different physical mechanism for generating fluctuations, the two-point function is identical to inflation. In this paper, we further explore this concept, focusing in particular on issues of non-gaussianity and quantum corrections. We find that the degeneracy with inflation is broken at three-point level: for the simplest case of an exponential potential, the three-point amplitude is strongly scale dependent, resulting in a breakdown of perturbation theory on small scales. However, we show that the perturbative breakdown can be circumvented -- and all issues raised in Linde et al. (arXiv:0912.0944) can be addressed -- by altering the potential such that power is suppressed on small scales. The resulting range of nearly scale invariant, gaussian modes can be as much as twelve e-folds, enough to span the scales probed by microwave background and large scale structure observations. On smaller scales, the spectrum is not scale invariant but is observationally acceptable.
42 pages, 1 figure
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