A Faster Growth of Perturbations in an Early Matter Dominated Epoch: Primordial Black Holes and Gravitational Waves

Abstract

We present a scenario for fast growth of cosmological perturbations; δ(t) ∼ a(t) s , a(t) being the scale factor, with 5 < s < 10 for the cases reported in this article. The basic ingredients of the scenario are an early matter dominated era and the dark fermion which experiences a scalar mediated force during the epoch. Both of these arise in string/supergravity models. The fast growth occurs for sub-horizon density perturbations of the dark fermion. The fast growth has a rich set of phenomenological implications. We outline implications for the formation of primordial black holes and the production of gravitational waves. Primordial black holes in the sub-lunar mass range (which are ideal dark matter candidates) can be produced. Gravitational waves can be produced in a wide range of frequencies due to second order scalar perturbations and due to evaporation and merger of primordial black holes.

Hunt for Light Primordial Black Hole Dark Matter with Ultra-High-Frequency Gravitational Waves

“…models [24][25][26]. Other non-standard scenarios invoke, for instance, preheating effects [27][28][29][30][31][32], early matter-domination [33][34][35][36][37] and collapse of cosmic strings [38][39][40][41][42][43]. As modes are stretched on super-horizon scales during inflation, curvature perturbations freeze-out until they re-enter the horizon during the post-inflationary epoch.…”