A review of the stochastic background of gravitational waves in f(R)
  gravity with WMAP constrains
  This paper is a review of previous works on the stochastic background of
gravitational waves (SBGWs) which has been discussed in various peer-reviewed
journals and international conferences. The SBGWs is analyzed with the aid of
the Wilkinson Microwave Anisotropy Probe (WMAP) data. We emphasize that, in
general, in previous works in the literature about the SBGWs, old Cosmic
Background Explorer (COBE) data were used. After this, we want to face the
problem of how the SBGWs and f(R) gravity (where f(R) is a function of the
Ricci scalar R) can be related, showing, vice versa, that a revealed SBGWs
could be a powerful probe for a given theory of gravity. In this way, it will
also be shown that the conform treatment of SBGWs can be used to parametrize in
a natural way f(R) theories. Some interesting examples which have been recently
discussed in the literature will be also analysed. The presence and the
potential detection of the SBGWs is quite important in the framework of the
debate on high-frequency gravitational waves (HFGWs) too. Recently, the
importance of HFGWs has been emphasized in some papers in the literature.
