Shortcomings of New Parametrizations of Inflation

TL;DR

This paper critiques recent phenomenological parametrizations of cosmic inflation, arguing they are inadequate for precise predictions and emphasizing the importance of connecting inflation models to fundamental physics.

Contribution

The paper provides critical analysis and examples showing the limitations of new inflation parametrizations and advocates for grounding inflation models in high-energy physics.

Findings

New parametrizations are not generic or sufficiently accurate.

Disconnecting inflation from fundamental physics may hinder understanding.

Current approaches may not meet the precision required by cosmological data.

Abstract

In the hope of avoiding model dependence of the cosmological observables, phenomenological parametrizations of Cosmic Inflation have recently been proposed. Typically, they are expressed in terms of two parameters associated with an expansion of the inflationary quantities matching the belief that inflation is characterized by two numbers only, the tensor-to-scalar ratio and the scalar spectral index. We give different arguments and examples showing that these new approaches are either not generic or insufficient to make predictions at the accuracy level needed by the cosmological data. We conclude that disconnecting inflation from high energy physics and gravity might not be the most promising way to learn about the physics of the early Universe.