Is the Dynamics of Tracking Dark Energy Detectable?

We highlight the unexpected impact of nucleosynthesis and other early universe constraints on the detectability of tracking quintessence dynamics at late times, showing that such dynamics may well be invisible until the unveiling of the Stage-IV dark energy experiments (DUNE, JDEM, LSST, SKA). Nucleosynthesis forces |w'(0)| < 0.2 for the models we consider and strongly limits potential deviations from LCDM. Surprisingly, the standard CPL parametrisation, w(z) = w_0 + w_a z/(1+z), cannot match the nucleosynthesis bound for minimally coupled tracking scalar fields. Given that such models are arguably the best-motivated alternatives to a cosmological constant these results may significantly impact future cosmological survey design and imply that dark energy may well be dynamical even if we do not detect any dynamics in the next decade.