Mechanisms for producing Primordial Black Holes from Inflationary Models Beyond Fine-Tuning

TL;DR

This paper analyzes the fine-tuning requirements in inflationary models for primordial black hole production, highlighting that models with step-like features and multifield setups are less fine-tuned and more observationally consistent.

Contribution

It compares single and multifield inflationary models, identifying less fine-tuned scenarios with potential observable signals for primordial black hole formation.

Findings

Models with step-like features require less fine-tuning.

Multifield models with spectator fields can reduce fine-tuning.

Some models predict low-frequency signals detectable by pulsar timing arrays.

Abstract

In this study, we present an analysis of the fine-tuning required in various inflationary models in order to explain the production of Primordial Black Holes (PBHs). We specifically examine the degree of fine-tuning necessary in two prominent single field inflationary models: those with an inflection point and those with step-like features in the potential. Our findings indicate that models with step-like features generally require less fine-tuning compared to those with an inflection point, making them more viable for consistent PBH production. An interesting outcome of these models is that, in addition to improved fine-tuning, they may also predict low-frequency signals that can be detected by pulsar timing array (PTA) collaborations. Additionally, we extend our analysis to multifield inflationary models to assess whether the integration of additional fields can further alleviate the fine-tuning demands. The study also explores the role of a spectator field and its impact on the fine-tuning process. Through a comparative analysis across these models, we evaluate their parametric sensitivities and alignment with the constraints from Cosmic Microwave Background (CMB) observations. Our results indicate that although mechanisms involving a spectator field can circumvent the issue of fine-tuning parameters for PBH production, both multifield models and models with step-like features present promising alternatives. While fine-tuning involves multiple considerations, our primary objective is to evaluate various inflationary models to identify the one that most naturally explains the formation of PBHs. Hence, this study aims to the development of less constrained inflationary scenarios that align with observational data and support the theoretical possibility of PBH production.