Large fluctuations and Primordial Black Holes

TL;DR

This paper reviews mechanisms of large primordial fluctuations leading to primordial black holes and scalar-induced gravitational waves, focusing on quantum loop corrections, constraints, and model extensions like Galileon and stochastic inflation.

Contribution

It provides a comprehensive analysis of quantum loop effects on PBH formation, explores methods to circumvent no-go constraints, and discusses advanced inflation models and their implications.

Findings

Severe no-go constraints on PBH production in single-field inflation due to loop corrections.

Effective field theory and renormalization techniques can help evade these constraints.

Scalar-induced gravitational waves are generated in specific inflationary setups.

Abstract

In this paper, we review in detail different mechanisms of generation of large primordial fluctuations and their implications for the production of primordial black holes (PBHs) and scalar-induced secondary gravity waves (SIGW), with the ultimate aim of understanding the impact of loop correction on quantum correlations and the power spectrum. To accomplish the goal, we provide a concise, comprehensive, but in depth review of conceptual and technical details of the standard model of the universe, namely, causal structure and inflation, quantization of primordial perturbations and field theoretic techniques such as "in-in" formalism needed for the estimation of loop correction to the power spectrum. We discuss at length the severe constraints (no-go) on PBH production in single-field inflation imposed by appropriately renormalized quantum loop corrections, computed while maintaining the validity of the perturbation framework and assuming sufficient inflation to address the causality problem. Thereafter, we discuss in detail the efforts to circumvent the no-go result in Galileon inflation, multiple sharp transition (MST)-induced inflation, and stochastic single field inflation using an effective field theoretic (EFT) framework applicable to a variety of models. We provide a thorough analysis of the Dynamical Renormalization Group (DRG) resummation approach, adiabatic and late-time renormalization schemes, and their use in producing solar and sub-solar mass PBHs. Additionally, we give a summary of how scalar-induced gravitational waves (SIGWs) are produced in MST setups and Galileon inflation.Finally, the PBH overproduction issue is thoroughly discussed.