Features in the primordial power spectrum: A running spectral index and formation of primordial black holes

We present an inflation model which realizes density fluctuations with a negative running spectral index large enough as inferred by WMAP observation. In this model two different stages of inflation occur successively in the observable regime. As a result of numerical investigation, we find that the fluctuations generated in the late first inflationary stage are enhanced to the level significant amount of primordial black holes could be produced due to parametric resonance and that it is stretched to a cosmological scale in the second inflation.