Thermodynamics of viscous dark energy for the late future time universe

Abstract

In this work we explore the thermodynamic aspects of dark energy for late future time universe in two different scenarios: as a perfect fluid with constant and variable equation of state parameter; and as dissipative fluid described by a barotropic equation of state with bulk viscosity in the framework of the Eckart theory and the full Israel-Stewart theory. We explore cosmological solutions for a flat, homogeneous and isotropic universe; and we assume the late future time behavior when the dark energy dominates the cosmic evolution. When modeled as a perfect fluid with a dynamical equation of state, $p=w(a)\rho$, the dark energy has an energy density, temperature and entropy well defined and an interesting result is that there is no entropy production even though been dynamical. For dissipative dark energy, in the Eckart theory two cases are studied: $\xi =const.$ and $\xi =(\beta /\sqrt{3}){\rho }^{1/2}$; it is found that the entropy grows exponentially for the first case and as a power-law for the second. In the Israel-Stewart theory we consider a $\xi ={\xi }_0{\rho }^{1/2}$ and a relaxation time $\tau =\xi /\rho$; an analytical Big Rip solution is obtained with a power-law entropy. In all cases a power-law relation between temperature and energy density is obtained. In order to maintain the second law of thermodynamics theoretical constraints for the equation of state are found in the different dark energy models studied. A barotropic dark fluid with $w<-1$ is thermodynamically difficult to support, but the overall effect of bulk viscosity in certain cases allows a phantom regime without thermodynamic anomalies.

12 pages

References in corpus (14)

• Viscous Cosmology for Early- and Late-Time Universe
• Bulk Viscous Cosmology
• Limits on $w$CDM from the EFTofLSS with the PyBird code
• Constraints on the curvature of the Universe and dynamical dark energy from the Full-shape and BAO data
• Dynamical dark energy after Planck CMB final release and $H_0$ tension
• Exploring a matter-dominated model with bulk viscosity to drive the accelerated expansion of the Universe
• Unified dark energy thermodynamics: varying w and the -1-crossing
• Accelerated and decelerated expansion in a causal dissipative cosmology
• Testing the equation of state for viscous dark energy
• Crossing the phantom divide with dissipative normal matter in the Israel-Stewart-Hiscock formalism
• Constraining viscous dark energy models with the latest cosmological data
• Stability analysis and constraints on interacting viscous cosmology
• Constraining a causal dissipative cosmological model
• Universe consisting of diffusive dark fluids: thermodynamics and stability analysis

Cited by in corpus (2)

• Note on bulk viscosity as an alternative to dark energy
• Accurate analytic approximation for a fractional differential equation with a modified Bessel function term