Reconciling the Tension Between Planck and BICEP2 Through Early Dark
  Energy
  We show the possibility that the observational results of the primordial
gravitational waves from Planck and BICEP2 for the tensor-to-scalar ratio $r$
can be reconciled when an early dark energy was included. This early dark
energy behaves like a radiation component at very early epoch. This is
equivalent to induce additional number of effective neutrino species: $\Delta
N_{eff}=[\frac{7}{8}(\frac{4}{11})^{4/3}]^{-1}\rho_{de}(a)/\rho_{\gamma}(a)$,
where $\rho_{\gamma}(a)$ is the photon energy density and the numerical factors
arise from converting to effective neutrino species. And $\rho_{de}(a)$ is the
energy density of early dark energy. Combining the Planck temperature data, the
WMAP9 polarization data, and the baryon acoustic oscillation data with and
without BICEP2 data, we find that in this early dark energy model the tension
between the observations from Planck and BICEP2 was relived at $2\sigma$
regions. But it cannot be removed completely due to the small ratio of early
dark energy constrained by the other cosmic observations. As a byproduct, the
tension between observed values of Hubble parameter from Planck and the direct
measurement of the Hubble constant was removed in this early dark energy model.
