Isocurvature perturbations and tensor mode in light of Planck and BICEP2
  We investigate the degeneracy of the isocurvature perturbations and the
primordial gravitational waves, by using recent observations of the cosmic
microwave background (CMB) reported by Planck and BICEP2 collaborations. We
show that the tension in the bound on the tensor-to-scalar ratio $r$ between
Planck and BICEP2 can be resolved by introducing the anti-correlated
isocurvature perturbations. Quantitatively, we find that with the
anti-correlated isocurvature perturbations the constraints on $r$ from Planck
alone and BICEP2 results can be consistent at 68 % C.L.
