Inflation in a viscous fluid model

TL;DR

This paper models inflation using a viscous fluid with bulk viscosity, demonstrating compatibility with Planck data, reconstructing the equation of state, and showing equivalence to scalar field descriptions.

Contribution

It introduces a viscous fluid model for inflation, reconstructs the EoS from observational data, and shows the model's consistency and equivalence with scalar field theories.

Findings

Fluid model matches Planck observables

Reconstructed EoS compatible with data

Graceful exit and singular inflation possible

Abstract

We explore a fluid description of the inflationary universe. In particular, we investigate a fluid model in which the equation of state (EoS) for a fluid includes bulk viscosity. We find that the three observables of inflationary cosmology: the spectral index of the curvature perturbations, the tensor-to-scalar ratio of the density perturbations, and the running of the spectral index, can be consistent with the recent Planck results. We also reconstruct the explicit EoS for a fluid from the spectral index of the curvature perturbations compatible with the Planck analysis. In the reconstructed models of a fluid, the tensor-to-scalar ratio of the density perturbations can satisfy the constraints obtained from the Planck satellite. The running of the spectral index can explain the Planck data. In addition, it is demonstrated that in the reconstructed models of a fluid, the graceful exit from inflation can be realized. Moreover, we show that the singular inflation can occur in a fluid model. Furthermore, we show that a fluid description of inflation can be equivalent to the description of inflation in terms of scalar field theories.