Primordial thermal gravitational waves from warm inflation

Abstract

Abstract For the first time, the possibility of generation of primordial thermal gravitational waves from warm inflation is investigated with the cosmic microwave background. The combined effect of thermal and squeezing effects can reduce the amplitude of the CMB BB-mode angular power spectrum for the parameter range ($0 \leq q \leq 1$ and $\zeta = 0,\pi/2$) considered in this work in both strong ($Q>>1$) and weak ($Q<<1$) warm inflationary models. In a thermal squeezed vacuum state, the BB-mode correlation angular power spectrum of warm inflation is found to be consistent with the dust-corrected joint constraints from $Planck$ and BK18 for both strong and weak dissipation regimes. The combined effect of thermal and squeezing phenomena in warm inflation is essential for achieving compatibility with current CMB BB-mode observations and predicts primordial thermal gravitational waves.