Relic gravitational waves in the light of 7-year Wilkinson Microwave
  Anisotropy Probe data and improved prospects for the Planck mission
  The new release of data from Wilkinson Microwave Anisotropy Probe improves
the observational status of relic gravitational waves. The 7-year results
enhance the indications of relic gravitational waves in the existing data and
change to the better the prospects of confident detection of relic
gravitational waves by the currently operating Planck satellite. We apply to
WMAP7 data the same methods of analysis that we used earlier [W. Zhao, D.
Baskaran, and L.P. Grishchuk, Phys. Rev. D 80, 083005 (2009)] with WMAP5 data.
We also revised by the same methods our previous analysis of WMAP3 data. It
follows from the examination of consecutive WMAP data releases that the maximum
likelihood value of the quadrupole ratio $R$, which characterizes the amount of
relic gravitational waves, increases up to $R=0.264$, and the interval
separating this value from the point $R=0$ (the hypothesis of no gravitational
waves) increases up to a $2\sigma$ level. The primordial spectra of density
perturbations and gravitational waves remain blue in the relevant interval of
wavelengths, but the spectral indices increase up to $n_s =1.111$ and
$n_t=0.111$. Assuming that the maximum likelihood estimates of the perturbation
parameters that we found from WMAP7 data are the true values of the parameters,
we find that the signal-to-noise ratio $S/N$ for the detection of relic
gravitational waves by the Planck experiment increases up to $S/N=4.04$, even
under pessimistic assumptions with regard to residual foreground contamination
and instrumental noises. We comment on theoretical frameworks that, in the case
of success, will be accepted or decisively rejected by the Planck observations.
