No evidence for dark energy metamorphosis

Recent attempts to fit type Ia supernova data by modelling the dark energy density as a truncated Taylor series have suggested the possibility of metamorphosis, i.e., a rapidly evolving equation of state parameter, wDE(z). However, we show that fits using that parametrization have significant problems. Evolution of wDE(z) is both favoured and in some sense forced, and the equation of state parameter blows up or diverges in large regions of the parameter space. To further elucidate these problems we have simulated sets of supernova data in a Λ-universe to show that the suggested 'evidence' for metamorphosis is also common for wDE = −1.