Interacting viscous matter with a dark energy fluid

TL;DR

This paper investigates a cosmological model with interacting dark energy and viscous matter, constrained by observational data, revealing negligible viscosity and a dark energy component close to phantom energy.

Contribution

It introduces a cosmological model with viscous matter interacting with dark energy and constrains it using multiple observational datasets.

Findings

Bulk viscosity constrained to be negligible by observations.

Dark energy barotropic index is negative and close to zero.

Model supports a phantom energy scenario.

Abstract

We study a cosmological model composed of a dark energy fluid interacting with a viscous matter fluid in a spatially flat Universe. The matter component represents the baryon and dark matter and it is taken into account, through a bulk viscosity, the irreversible process that the matter fluid undergoes because of the accelerated expansion of the universe. The bulk viscous coefficient is assumed to be proportional to the Hubble parameter. The radiation component is also taken into account in the model. The model is constrained using the type Ia supernova observations, the shift parameter of the CMB, the acoustic peak of the BAO and the Hubble expansion rate, to constrain the values of the barotropic index of dark energy and the bulk viscous coefficient. It is found that the bulk viscosity is constrained to be negligible (around zero) from the observations and that the barotropic index for the dark energy to be negative and close to zero too, indicating a phantom energy.