Abstract

One propery of a popular class of dark energy models is the tracking behaviour of the dominant energy component so that the dark energy density will sub-dominantly track the evolution of the dominant component and can be never negligible with respect to radiation and matter. Dark energy could therefore be present not only in the late universe but also in early times as suggested by several models of “early” dark energy (EDE). In this talk I will discuss the future constraints on EDE parameters achievable by the Planck and CMB Pol experiments considering the possibility of EDE clustering through a sound speed < 1 (cold dark energy) and the presence of anisotropic stresses. In particular I will show how a detection of the lensing signal of the CMB can significantly improve the constraints on EDE . Finally I will discuss how the recent indications (at one confidence level) for an extra background of relativistic particles can be partially explained by EDE .