Ghost Inflation

TL;DR

Ghost Inflation presents an inflationary scenario driven by ghost condensation, eliminating the need for a slow-roll potential. Density perturbations arise from the non-relativistic $\pi$ fluctuations with a scale-invariant spectrum ($n_s=1$) and negligible tensor modes, while predicting sizable, distinctive non-Gaussianities from derivative interactions. The approach operates within an EFT around the ghost condensate, enabling inflation at much lower energy scales than standard models and yielding testable predictions for the CMB bispectrum. If forthcoming observations detect $n_s=1$ with a characteristic non-Gaussian pattern and no primordial gravitational waves, this framework would be sharply supported; conversely, any deviation in $n_s$ or detection of tensor modes could rule it out.

Abstract

We propose a new scenario for early cosmology, where an inflationary de Sitter phase is obtained with a ghost condensate. The transition to radiation dominance is triggered by the ghost itself, without any slow-roll potential. Density perturbations are generated by fluctuations around the ghost condensate and can be reliably computed in the effective field theory. The fluctuations are scale invariant as a consequence of the de Sitter symmetries, however, the size of the perturbations are parametrically different from conventional slow-roll inflation, and the inflation happens at far lower energy scales. The model makes definite predictions that distinguish it from standard inflation, and can be sharply excluded or confirmed by experiments in the near future. The tilt in the scalar spectrum is predicted to vanish (n_s=1), and the gravity wave signal is negligible. The non-Gaussianities in the spectrum are predicted to be observable: the 3-point function is determined up to an overall order 1 constant, and its magnitude is much bigger than in conventional inflation, with an equivalent f_NL ~ 100, not far from the present WMAP bounds.