Primordial Black Holes from a tiny bump/dip in the Inflaton potential

Primordial Black Holes, formed in the early universe during the hot Big Bang phase, have important implications for a number of cosmic conundra.  This talk is about the formation of primordial black holes. Scalar perturbations during inflation can be substantially amplified by tiny features in the inflaton potential. A bump-like feature behaves like a local speed-breaker and lowers the speed of the scalar field, thereby locally enhancing the scalar power spectrum. A bump-like feature emerges naturally if the base inflaton potential contains a  positive local correction term, which leads to a large peak in the curvature power spectrum and to an enhanced probability of black hole formation. Remarkably this does not significantly affect the scalar spectral tilt on CMB scales. Consequently such models can produce higher mass primordial black holes (M_PBH ≥ 1 M_sun) that are important for LIGO observations. This is in contrast to models with `near inflection-point potentials' in which generating higher mass black holes severely affects the  CMB observables.   Interestingly, the results remain valid if the bump is replaced by a dip implying a negative local correction to the inflaton potential. With a generic choice of plateau base potential, the amplification of primordial scalar power spectrum can be large enough leading to a significant contribution of primordial black holes (PBHs) to the dark matter density at the present epoch.