Figure 4
From: Stochastic backgrounds of relic gravitons: a theoretical appraisal
The spectral energy density of relic gravitons in the minimal TΛCDM scenario where the post-inflationary thermal history contemplates a phase where the sound speed of the plasma c st is close to the speed of light c. In the plot at the right cst = c (corresponding to a constant barotropic index wt = 1); in the plot at the left cst = 0.77 c (corresponding to a constant barotropic index wt = 0.6). In both plots the other cosmological parameters have been chosen to coincide with the best fit to the WMAP 5-yr data alone.