Singularities and Soft-Big Bang in a viscous $\Lambda$CDM model

Abstract

In this paper we explore the different types of singularities that arise in the $\Lambda$CDM model when dissipative processes are considered, in the framework of the Eckart's theory. In particular, we study the late-time behavior of $\Lambda$CDM model with viscous cold dark matter (CDM) and an early-time viscous radiation domination era with cosmological constant (CC). The fluids are described by the barotropic equation of state (EoS) $p=(\gamma -1)\rho$, where $p$ is the equilibrium pressure of the fluid, $\rho$ their energy density, and $\gamma$ is the barotropic index. We explore two particular cases for the bulk viscosity $\xi$, a constant bulk viscosity $\xi ={\xi }_0$, and a bulk viscosity proportional to the energy density of the fluid $\xi ={\xi }_0\rho$. Due to some previous investigations that have explored to describe the behavior of the universe with a negative CC, we extend our analysis to this case. We found that future singularities like Big-Rip are allowed but without having a phantom EoS associated to the DE fluid. Big-Crunch singularities also appears when a negative CC is present, but also de Sitter and even Big-Rip types are allowed due to the negative pressure of the viscosity, which opens the possibility of an accelerated expansion in AdS cosmologies. We also discuss a very particular solution without Big Bang singularity that arises in the early-time radiation dominant era of our model known as Soft-Big Bang.

17 pages, 13 figures

References in corpus (9)

• Dark energy cosmology: the equivalent description via different theoretical models and cosmography tests
• The AdS_5xS^5 superstring worldsheet S-matrix and crossing symmetry
• Using Pantheon and DES supernova, baryon acoustic oscillation, and Hubble parameter data to constrain the Hubble constant, dark energy dynamics, and spatial curvature
• Negative cosmological constant in the dark sector?
• Cosmic viscosity as a remedy for tension between PLANCK and LSS data
• Accelerated and decelerated expansion in a causal dissipative cosmology
• An analysis of the $H_0$ tension problem in a universe with a viscous dark fluid
• Viscous universe with cosmological constant
• Exact solutions of a Flat Full Causal Bulk viscous FRW cosmological model through factorization