Beyond the perfect fluid hypothesis for dark energy equation of state

TL;DR

This paper explores nonlinear dark energy equations of state beyond perfect fluids, testing their cosmological implications against observational data and linking them to scalar field models, offering alternatives to phantom energy for cosmic acceleration.

Contribution

It introduces nonlinear equations of state for dark energy, tests them with observational data, and connects them to scalar field models, expanding beyond the perfect fluid assumption.

Findings

Nonlinear EoS models fit observational data well.

Replacing perfect fluid EoS allows cosmic acceleration without phantom energy.

Scalar field potentials can reproduce these nonlinear EoS models.

Abstract

Abandoning the perfect fluid hypothesis, we investigate here the possibility that the dark energy equation of state (EoS) $w$ is a nonlinear function of the energy density $\rho$. To this aim, we consider four different EoS describing classical fluids near thermodynamical critical points and discuss the main features of cosmological models made out of dust matter and a dark energy term with the given EoS. Each model is tested against the data on the dimensionless coordinate distance to Type Ia Supernovae and radio galaxies, the shift and the acoustic peak parameters and the positions of the first three peaks in the anisotropy spectrum of the comic microwave background radation. We propose a possible interpretation of each model in the framework of scalar field quintessence determining the shape of the self interaction potential $V(\phi)$ that gives rise to each one of the considered thermodynamical EoS. As a general result, we demonstrate that replacing the perfect fluid EoS with more generar expressions gives both the possibility of successfully solving the problem of cosmic acceleration escaping the resort to phantom models.