Foundations of observing dark energy dynamics with the Wilkinson Microwave Anisotropy Probe

Detecting dark energy dynamics is the main quest of current dark energy research. Addressing the issue demands a fully consistent analysis of cosmic microwave background, large-scale structure and SN-Ia data with multiparameter freedom valid for all redshifts. Here we undertake a ten parameter analysis of general dark energy confronted with the first year Wilkinson Microwave Anisotropy Probe, 2dF galaxy survey and latest SN-Ia data. Despite the huge freedom in dark energy dynamics there are no new degeneracies with standard cosmic parameters apart from a mild degeneracy between reionization and the redshift of acceleration, both of which effectively suppress small scale power. Breaking this degeneracy will help significantly in detecting dynamics, if it exists. Our best-fit model to the data has significant late-time evolution at $z<1.5$. Phantom models are also considered and we find that the best-fit crosses $w=-1$ which, if confirmed, would be a clear signal for radically new physics. Treatment of such rapidly varying models requires careful integration of the dark energy density usually not implemented in standard codes, leading to crucial errors of up to 5%. Nevertheless cosmic variance means that standard $\Lambda$ cold dark matter models are still a very good fit to the data and evidence for dynamics is currently very weak. Independent tests of reionization or the epoch of acceleration (e.g., integrated Sachs-Wolfe–large scale structure correlations) or reduction of cosmic variance at large scales (e.g., cluster polarization at high redshift) may prove key in the hunt for dynamics.