The Influence of Quintessence on the Separation of CMB Peaks

A hypothetical dark energy component may have an equation of state that is different from a cosmological constant and possibly even changing in time. The spacing of the cosmic microwave background peaks is sensitive to the ratio of the horizon sizes today and at last scattering and therefore to the details of the cosmological evolution. Together with independent measurements of today's cosmological parameters, this restricts quintessence models in the epoch before and during decoupling. For fixed \Omega^b_0, \Omega^{cdm}_0 and h, we give an analytic estimate of the spacing that depends on \Omega^{\phi}_{ls}, \Omega^{\phi}_0 and an effective equation of state of the dark energy component.