Hint of relic gravitational waves in the Planck and WMAP data
  Relic gravitational waves (RGWs) leave well-understood imprints on the
anisotropies in the temperature and polarization of cosmic microwave background
(CMB) radiation. In the TT and TE information channels, which have been well
observed by WMAP and Planck missions, RGWs compete with density perturbations
mainly at low multipoles. It is dangerous to include high-multipole CMB data in
the search for gravitational waves, as the spectral indices may not be
constants. In this paper, we repeat our previous work [W.Zhao & L.P.Grishchuk,
Phys.Rev.D {\bf 82}, 123008 (2010)] by utilizing the Planck TT and WMAP TE data
in the low-multipole range $\ell\le100$. We find that our previous result is
confirmed {with higher confidence}. The constraint on the tensor-to-scalar
ratio from Planck TT and WMAP TE data is $r\in [0.06,~0.60]$ (68% C.L.) with
the maximum likelihood at around $r\sim 0.2$. Correspondingly, the spectral
index at the pivot wavenumber $k_*=0.002$Mpc$^{-1}$ is
$n_s=1.13^{+0.07}_{-0.08}$, which is larger than 1 at more than $1\sigma$
level. So, we conclude that the new released CMB data indicate a stronger hint
for the RGWs with the amplitude $r\sim 0.2$, which is hopeful to be confirmed
by the imminent BICEP and Planck polarization data.
