Viscous universe with cosmological constant
- PDF / 692,927 Bytes
- 13 Pages / 439.37 x 666.142 pts Page_size
- 68 Downloads / 170 Views
Viscous universe with cosmological constant Jinwen Hua , Huan Hu School of Physics and Technology, Wuhan University, Wuhan 430060, China Received: 16 May 2020 / Accepted: 19 July 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We investigated a bulk viscous fluid universe with cosmological constant Λ by assuming that the bulk viscosity to be proportional to the Hubble parameter. We found that for an expanding universe, the (relative) matter density will be always greater than a nonzero constant and tends to this nonzero constant in the future. We show that the bulk viscosity model has a significantly better fitting to the combined SNe Ia + CMB + BAO + H(z) data than the ΛCDM model. Generally, the evolution or values of some cosmological parameters predicted by the bulk viscosity model do not deviate significantly from which are obtained from the ΛCDM model since the bulk viscosity coefficient obtained from the astronomical observational data is so small. We also made a statefinder analysis of the bulk viscosity model and found that the evolution of the {r, s} parameters behaves in such a way that 0 < s < 1, 0.945 < r < 1, indicating the bulk viscosity model is different from the ΛCDM model and the other “dark energy” model.
1 Introduction Observations data, for instance the data from type Ia supernovae [1, 2], the large-scale structure of universe [3] and cosmic microwave background (CMB) [4], indicated that our universe is spatially flat and accelerating, which is considered that there exists an exotic cosmic fluid (called the dark energy) that accounts for about 2/3 of the total energy of the universe. Despite the observational evidence on this existence of “dark energy,” its fundamental and nature origin is still unknown, resulting in many models have been proposed. Generally there are two different types of model. The first one is to modify the right side of the Einstein equation by introducing a special energy-momentum tensor T μν with a negative pressure. The simplest model for this type of model is the ΛCDM model, which introduce a cosmological constant Λ as the dark energy, and the ΛCDM model is characterized by the equation of state, i.e., ω −1. However, there exist some problems in the ΛCDM model, such as the coincidence problem [5], which refers to the coincidence that in today’s universe the matter density and the dark energy density happen to be the same order of magnitude although they evolve at a different way. A possible answer to this question is that the dark energy is dynamical. On the other hand, the process of dissipation arose in the viscous fluid, including both shear viscosity and bulk viscosity, as many studies shown, may be involved in the evolution of universe as an important role [6–8]. Eckart [9], Landau and Lifshitz [10] first studied the relativistic viscous fluid and derived the parabolic differential equations. But they just
a e-mail: [email protected] (corresponding author)
0123456789().: V,-vol
123
718
Page 2
Data Loading...
