Ghost Inflation

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 ex-cluded 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 negligi-ble. The non-Gaussianities in the spectrum are predicted to be observable: the 3-point function is determined up to an overall O (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.