Figure 2

The spectral energy density of the relic gravitons is illustrated the context of the ΛCDM scenario and for different values of r _T (see Eqs. (1.2)-(1.3)). In the plot at the right the tensor spectral index n_T does depend upon the frequency (α_T follows from Eq. (1.6) with the ΛCDM choice of parameters). The plot at the left corresponds to α_T = 0.