Mode - mode coupling and primordial fluctuations

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We consider the influence of mode - mode coupling in the inflaton field on the spectrum of primordial fluctuations. To this end, we formulate a phenomenological model where the inflaton fluctuations are treated as a fluid undergoing turbulent motion. Under suitable assumptions, it is possible to estimate the size and scale of fluctuations in velocity, which upon reheating induce corresponding fluctuations in the radiation energy density. For De Sitter inflation the resulting spectrum is scale invariant on all scales of interest. The amplitude of the resulting spectrum is compatible with known observational limits. This suggests that the hypothesis of a extremely weakly coupled inflation could be relaxed without affecting the predictions of the model. Principal PACS No 98.80.Cq; additional PACS nos: 04.62.+v, 11.10.Wx, 47.27