Inflationary universe in terms of a van der Waals viscous fluid

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\^ıtre-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.

7 pages, no figures, to appear in IJGMMP

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• The Classical and Loop Quantum Cosmology Phase Space of Interacting Dark Energy and Superfluid Dark Matter
• Gravitational Waves in the Presence of Viscosity
• Integrable Cosmological Model with van der Waals Gas and Matter Creation
• Symmetry operators and separation of variables in the $(2+1)$-dimensional Dirac equation with external electromagnetic field
• Causal cosmology with braneworld gravity including Gauss Bonnet coupling