Thermal gravitational waves from warm inflation

For the first time, the possibility of generation of thermal gravitational waves from warm inflation is investigated with cosmic microwave background. Gravitons produced from the quantum fluctuations during warm inflation are found to carry the thermal features if they exist in a thermal squeezed vacuum state. Thermal squeezing reduces the amplitude of the BB mode angular power spectrum of CMB when compared with the conventional cold inflation. This work inspects the thermal nature of tensor power spectrum from warm inflation and the relevance of quantum fluctuations over the thermal fluctuations. The dust corrected lensed BB modes from joint analysis of $Planck$ and BICEP2/$Keck$ for warm inflation provide compelling evidence for the existence of thermal gravitons.