Inflation in Terms of a Viscous van der Waals Coupled Fluid

TL;DR

This paper models early universe inflation using a coupled two-fluid system with a viscous van der Waals equation of state, deriving analytical solutions and comparing predictions with Planck data.

Contribution

It introduces a novel inflationary model combining viscous van der Waals fluids and coupled matter, providing analytical solutions and observational consistency.

Findings

Analytic expressions for the Hubble parameter were derived.

The model's predictions for spectral index and tensor-to-scalar ratio agree with Planck data.

The approach offers a new perspective on early universe acceleration mechanisms.

Abstract

We propose to describe the acceleration of the universe by introducing a model of two coupled fluids. We focus on the accelerated expansion at the early stages. The inflationary expansion is described in terms of a van der Waals equation of state for the cosmic fluid, when account is taken of bulk viscosity. We assume that there is a weak interaction between the van der Waals fluid and the second component (matter). The gravitational equations for the energy densities of the two components are solved for a homogeneous and isotropic Friedmann-Robertson-Walker universe, and analytic expressions for the Hubble parameter are obtained. The slow-roll parameters, the spectral index, and the tensor-to-scalar ratio are calculated and compared with the most recent astronomical data from the Planck satellite. Given reasonable restriction on the parameters, the agreement with observations is favorable.