Scalar spectral index in the presence of Primordial Black Holes

We study the cosmological consequences of energy injection from the evaporation of Primordial Black Holes (PBHs) that are formed due to the collapse of the inhomogeneities that were generated during inflation in the early universe. By using the current results of the baryon-photon ratio obtained from BBN and CMB observations, we impose constraints on the spectral index of perturbations on those small scales that cannot be estimated through CMB anisotropy and CMB distortions. The masses of the PBHs constrained in this study lie in the range of 10(9)-10(11) g, which corresponds to those PBHs whose maximal evaporation took place during the redshifts 10(6) < z < 10(9). It is shown that the upper bound on the scalar spectral index, n(s) can be constrained for a given threshold value, zeta(th), of the curvature perturbations for PBHs formation. Using Planck results for cosmological parameters, we obtained n(s) < 1.309 for zeta(th) = 0.7 and n(s) < 1.334 for zeta(th) = 1.2, respectively. The density fraction that has contributed to the formation of PBHs has also been estimated.