Inflationary universe in terms of a van der Waals viscous fluid

TL;DR

This paper models the early universe's inflationary expansion using a van der Waals fluid with viscosity, deriving analytical solutions and comparing key inflationary parameters with observational data, showing viscosity improves model accuracy.

Contribution

It introduces a novel inflationary model based on a viscous van der Waals fluid and demonstrates its consistency with recent cosmological observations.

Findings

Analytic expression for the scale factor during inflation.

The viscosity term enhances the model's agreement with observational data.

The model's parameters can be constrained to fit Planck satellite results.

Abstract

The inflationary expansion of our early-time universe is considered in terms of the van der Waals equation, as equation of state for the cosmic fluid, where a bulk viscosity contribution is assumed to be present. The corresponding gravitational equations for the energy density in a homogeneous and isotropic Friedmann-Lema\^{\i}tre-Robertson-Walker universe are solved, and an analytic expression for the scale factor is obtained. Attention is paid, specifically, to the role of the viscosity term in the accelerated expansion; the values of the slow-roll parameters, the spectral index, and the tensor-to-scalar ratio for the van der Waals model are calculated and compared with the most recent astronomical data from the Planck satellite. By imposing reasonable restrictions on the parameters of the van der Waals equation, in the presence of viscosity, it is shown to be possible for this model to comply quite precisely with the observational data. One can therefore conclude that the inclusion of viscosity in the theory of the inflationary epoch definitely improves the cosmological models.