Comment on "Inflation with a graceful exit and entrance driven by Hawking radiation"

TL;DR

This paper critiques a cosmological inflation model driven by Hawking-like radiation, arguing that its proposed 'turn on' mechanism is incompatible with the apparent horizon of the early universe and conflicts with observational constraints.

Contribution

It clarifies the limitations of applying Hawking radiation concepts to early universe inflation within FRW models, highlighting theoretical and observational inconsistencies.

Findings

The 'turn on' mechanism is incompatible with FRW apparent horizon.

The model predicts a density ratio exceeding COBE constraints.

Hawking-like radiation cannot be straightforwardly applied to early universe inflation.

Abstract

Modak and Singleton [Phys. Rev. D 86, 123515 (2012)] have presented Hawking-like radiation for cosmological inflation which has a natural "turn on" and a natural "turn off" mechanism. This Hawking-like radiation results in an effective negative pressure "fluid" which leads to a rapid period of expansion in the very early Universe. We discuss that the turn on mechanism can not happen for FRW model in early universe because its horizon is apparent horizon not event horizon. Hence, we cannot apply geometric optic approximation which is a necessary condition for tunneling method. It was shown that this model predict a value for $\frac{\rho}{m_{pl}^4}$ which is bigger than the COBE normalization constraint in the Cosmic Microwave Background (CMB) at the horizon exit.