Constraints on early dark energy from CMB lensing and weak lensing
  tomography
  Dark energy can be studied by its influence on the expansion of the Universe
as well as on the growth history of the large-scale structure. In this paper,
we follow the growth of the cosmic density field in early dark energy
cosmologies by combining observations of the primary CMB temperature and
polarisation power spectra at high redshift, of the CMB lensing deflection
field at intermediate redshift and of weak cosmic shear at low redshifts for
constraining the allowed amount of early dark energy. We present these
forecasts using the Fisher-matrix formalism and consider the combination of
Planck-data with the weak lensing survey of Euclid. We find that combining
these data sets gives powerful constraints on early dark energy and is able to
break degeneracies in the parameter set inherent to the various observational
channels. The derived statistical 1-sigma-bound on the early dark energy
density parameter is sigma(Omega_d^e)=0.0022 which suggests that early dark
energy models can be well examined in our approach. In addition, we derive the
dark energy figure of merit for the considered dark energy parameterisation and
comment on the applicability of the growth index to early dark energy
cosmologies.
