Primordial blackholes from Gauss-Bonnet-corrected single field inflation

TL;DR

This paper proposes a novel mechanism for primordial blackhole formation involving a scalar field coupled to the Gauss-Bonnet term, which enhances curvature perturbations and generates detectable gravitational waves.

Contribution

It introduces a new model where the balance of scalar potential and Gauss-Bonnet coupling seeds blackholes and sources gravitational waves, expanding inflationary blackhole formation theories.

Findings

Primordial blackholes can form when scalar potential and Gauss-Bonnet coupling are balanced.

The model predicts significant second-order gravitational wave signals.

Potential detectability of gravitational waves by future experiments.

Abstract

Primordial blackholes formed in the early Universe via gravitational collapse of over-dense regions may contribute a significant amount to the present dark matter relic density. Inflation provides a natural framework for the production mechanism of primordial blackholes. For example, single field inflation models with a fine-tuned scalar potential may exhibit a period of ultra-slow roll, during which the curvature perturbation may be enhanced to become seeds of the primordial blackholes formed as the corresponding scales reenter the horizon. In this work, we propose an alternative mechanism for the primordial blackhole formation. We consider a model in which a scalar field is coupled to the Gauss-Bonnet term and show that primordial blackholes may be seeded when a scalar potential term and the Gauss-Bonnet coupling term are nearly balanced. Large curvature perturbation in this model not only leads to the production of primordial blackholes but it also sources gravitational waves at the second order. We calculate the present density parameter of the gravitational waves and discuss the detectability of the signals by comparing them with sensitivity bounds of future gravitational wave experiments.