A dark energy view of inflation

Traditionally, inflationary models are analyzed in terms of parameters such as the scalar spectral index ns and the tensor to scalar ratio r, while dark energy models are studied in terms of the equation of state parameter w. Motivated by the fact that both deal with periods of accelerated expansion, we study the evolution of w during inflation, in order to derive observational constraints on its value during an earlier epoch likely dominated by a dynamic form of dark energy. We find that the cosmic microwave background and large-scale structure data is consistent with w_inflation=-1 and provides an upper limit of 1+w <~ 0.02. Nonetheless, an exact de Sitter expansion with a constant w=-1 is disfavored since this would result in ns=1.