We show that the new precise measurements of Cosmic Microwave Background ( CMB ) temperature and polarization anisotropies made by the Planck satellite significantly improves previous constraints on the cosmic gravitational waves background ( CGWB ) at frequencies f > 10 ^ { -15 } Hz .
On scales smaller than the horizon at the time of decoupling , primordial gravitational waves contribute to the total radiation content of the Universe .
Considering adiabatic perturbations , CGWB affects temperature and polarization CMB power spectra and matter power spectrum in a manner identical to relativistic particles .
Considering the latest Planck results we constrain the CGWB energy density to \Omega _ { gw } h ^ { 2 } < 1.7 \times 10 ^ { -6 } at 95 % CL .
Combining CMB power spectra with lensing , BAO and primordial Deuterium abundance observations , we obtain \Omega _ { gw } h ^ { 2 } < 1.2 \times 10 ^ { -6 } at 95 % CL , improving previous Planck bounds by a factor 3 and the recent direct upper limit from the LIGO and VIRGO experiments a factor 2 .
A combined analysis of future satellite missions as COrE and EUCLID could improve current bound by more than an order of magnitude .