Constraints on the Spacetime Dynamics of an Early Dark Energy Component
  We consider an Early Dark Energy (EDE) cosmological model, and perform an
analysis which takes into account both background and perturbation effects via
the parameters $c^{2}_{\rm eff}$ and $c^{2}_{\rm vis}$, representing effective
sound speed and viscosity, respectively. By using the latest available data we
derive constraints on the amount of dark energy at early times and the present
value of the equation of state. Our focus is on the effect that early dark
energy has on the Cosmic Microwave Background (CMB) data, including
polarization and lensing, in a generalized parameter space including a varying
total neutrino mass, and tensor to scalar ratio, besides the 6 standard
parameters of the minimal cosmological model. We find that the inclusion of
Baryonic Acoustic Oscillations (BAO) data and CMB lensing significantly
improves the constraints on the EDE parameters, while other high redshift data
like the Quasar Hubble diagram and the Lyman-$\alpha$ forest BAO have instead a
negligible impact. We find $\Omega_{\rm eDE} < 0.00391 $ and $w_{0} < -0.9500 $
at the $95 \%$ C.L. for EDE accounting for its clustering through the inclusion
of perturbation dynamics. This limit becomes weaker $\Omega_{\rm eDE} <
0.00337$ if perturbations are neglected. The constraints on the EDE parameters
are remarkably stable even when $\Sigma m_{\nu}$, and $r$ parameters are
varied, with weak degeneracies between $\Omega_{\rm eDE}$ and $r$ or $\Sigma
m_{\nu}$. Perturbation parameters are not constrained with current data sets,
and tensions between the CMB derived $H_0$ and $\sigma_8$ values and those
measured with local probes are not eased. This work demonstrates the capability
of CMB probes to constrain the total amount of EDE well below the percent
level.
