The presence of Primordial Gravitational Waves in the Cosmic Microwave   Background
  The General Relativity affirms that any field is a source of gravitational field, thus one should affirm that the energy of Cosmic Microwave Background (CMB) generated primordial gravitational waves. The present article shows that a gravitational wave with dimensionless amplitude $\sim 10^{-5}$ and large wave length $\sim 10$ megaparsecs shifts temperature of CMB radiation about of a part in $10^{5}$. 
Wytler Cordeiro dos Santos
gr-qc astro-ph.CO astro-ph.HE hep-th