# Primordial Black Holes from Thermal Inflation

## TL;DR

This paper proposes a new mechanism for primordial black hole formation involving thermal and fast-roll inflation phases, potentially explaining dark matter and supermassive black hole seeds.

## Contribution

It introduces a novel PBH production mechanism based on thermal inflation followed by tachyonic fast-roll inflation, with specific parameter conditions for dark matter and supermassive black hole seeds.

## Key findings

- PBHs can account for dark matter with a thermal inflaton mass of about 10^6 GeV.
- Seed formation for supermassive black holes is possible with a 1 GeV inflaton mass.
- A concrete realization via a running mass model is presented.

## Abstract

We present a novel mechanism for the production of primordial black holes (PBHs). The mechanism is based on a period of thermal inflation followed by fast-roll inflation due to tachyonic mass of order the Hubble scale. Large perturbations are generated at the end of the thermal inflation as the thermal inflaton potential turns from convex to concave. These perturbations can lead to copious production of PBHs when the relevant scales re-enter horizon. We show that such PBHs can naturally account for the observed dark matter in the Universe when the mass of the thermal inflaton is about $10^6\,$GeV and its coupling to the thermal bath preexisting the late inflation is of order unity. We consider also the possibility of forming the seeds of the supermassive black holes. In this case we find that the mass of the thermal inflaton is about $1\,$GeV, but its couplings have to be very small, $\sim 10^{-7}$. Finally we study a concrete realisation of our mechanism through a running mass model.