Fine Tuning May Not Be Enough

TL;DR

This paper argues that the challenges of fine-tuning in scalar-driven inflation are more severe than previously thought, due to quantum effects from matter fields affecting the inflaton potential during reheating.

Contribution

It reveals that the effective potential in de Sitter space depends intricately on the ratio of the inflaton field to the Hubble parameter, complicating fine-tuning solutions.

Findings

Vacuum fluctuations of matter fields alter the inflaton potential.

Effective potential depends on the ratio /H.

H factors in de Sitter are non-local and not Planck-suppressed.

Abstract

We argue that the fine tuning problems of scalar-driven inflation may be worse than is commonly believed. The reason is that reheating requires the inflaton to be coupled to other matter fields whose vacuum fluctuations alter the inflaton potential. The usual response has been that even more fine-tuning of the classical potential $V(\varphi)$ can repair any damage done in this way. We point out that the effective potential in de Sitter background actually depends in a complicated way upon the dimensionless combination of $\varphi/H$. We also show that the factors of $H$ which occur in de Sitter do not even correspond to local functionals of the metric for general geometries, nor are they Planck-suppressed.