WMAP constraints on quintessence

We use recent results from the Wilkinson Microwave Anisotropy Probe for the locations of peaks and troughs of the cosmic microwave background power spectrum, together with constraints from large-scale structure, to study a quintessence model in which the pure exponential potential is modified by a polynomial factor. Our analysis, in the (Ω_m,h,n_s) cosmological parameter space and for a wide range of potential parameters, shows that quintessence is favored compared to the cold dark matter model with a cosmological constant (ΛCDM) for n_s≈1 and relatively high values of the average fraction of dark energy before last scattering (“early quintessence”); for n_s<1, quintessence and ΛCDM give similar results, except for high values of early quintessence, in which case ΛCDM is favored.