Constraints on Inflationary Solutions in the Presence of Shear and Bulk Viscosity

TL;DR

This paper investigates how the reality condition and the inclusion of shear and bulk viscosity constrain inflationary models within the FLRW framework, often excluding or limiting many existing models.

Contribution

It systematically analyzes the impact of the reality condition and viscous effects on the viability of inflationary models, providing new constraints and exclusions.

Findings

Many inflationary models are excluded by the reality condition.

Viscous effects impose additional constraints on model parameters.

The reality condition restricts the dynamical relationship between scale factor and potential.

Abstract

Inflationary models and their claim to solve many of the outstanding problems in cosmology have been the subject of a great deal of debate over the last few years. A major sticking point has been the lack of both good observational and theoretical arguments to single out one particular model out of the many that solve these problems. Here we examine the degree of restrictiveness on the dynamical relationship between the cosmological scale factor and the inflation driving self-interaction potential of a minimally coupled scalar field, imposed by the condition that the scalar field is required to be real during a classical regime (the reality condition). We systema\-tically look at the effects of this constraint on many of the inflationary models found in the literature within the FLRW framework, and also look at what happens when physically motivated perturbations such as shear and bulk viscosity are introduced. We find that in many cases, either the models are totally excluded or the reality condition gives rise to constraints on the scale factor and on the various parameters of the model.