Causal Bulk Viscous Fluid Research Articles

Spatially flat matter-dominated universe filled with barotropic causal bulk viscous fluid: a symmetry-based approach

We have studied a spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) cosmological model with an additional assumption that the universe is filled with barotropic causal bulk viscous fluid. The bulk viscous coefficient of the fluid is related to the energy density and relaxation time by the relation . We have used a truncated version of the transport equation for the viscous pressure. The expansion rate of such a spatially flat FLRW universe is governed by the well-known modified Painlevé–Ince equation. We find that the Lie symmetry corresponding to scale invariance gives the power-law solution for this model equation from invariant curve condition. For the value of , our result satisfies the present experimental value of the deceleration parameter (q) for . The result obtained for the relaxation time which is of the order of the Hubble time supports the necessary condition for successful inflation. Our study not only shows the role of the bulk viscosity for the present accelerating expansion but also predicts an age of around , which solves the age problem of the present universe.

PERFECT FLUID COSMOLOGICAL MODELS WITH TIME-VARYING CONSTANTS

In this paper, we study in detail a perfect fluid cosmological model with time-varying "constants" using dimensional analysis and the symmetry method. We examine the case of variable "constants" in detail without considering the perfect fluid model as a limiting case of a model with a causal bulk viscous fluid as discussed in a recent paper. We obtain some new solutions through the Lie method and show that when matter creation is considered, these solutions are physically relevant.

Iterative solutions for relativistic dissipative cosmologies

Iterative solutions of the gravitational field equations for a homogeneous flat Friedmann–Robertson–Walker Universe filled with a causal bulk viscous fluid in the framework of the full Israel–Stewart–Hiscock theory are presented. The general solution of the field equations are presented in a parametric form in the zeroth-, first-, second-, and mth-order approximation by the method of iteration. The time evolution of the scale factor, energy density, deceleration parameter, entropy, Kretschmann scalar, and bulk viscous pressure-thermodynamic pressure ratio for a Zeldovich fluid-filled space-time are discussed. PACS Nos.: 98.80-k, 04.20Jb

New Classes of Exact Causal Viscous Cosmologies

Two particular exact solutions of thegravitational field equations for a homogeneous flatFriedmann-Robertson-Walker universe filled with a causalbulk viscous fluid in the framework of the fullIsrael-Stewart-Hiscock theory are presented. The dynamics of theuniverse is entirely determined in the present models byits thermal behavior. The solutions of the fieldequations are expressed in an exact closed parametric form and correspond to an inflationarytransition between a singular state and a Minkowskianspace-time and a quasi-Minkowskian era and aninflationary state, connected by a noninflationaryphase, respectively. The inflationary era of the first solution isassociated with an increase in temperature and energydensity (a heating period), but with a decrease of thecomoving entropy. The evolutionary period described by the second solution leads during itsnoninflationary phase to a rapid decrease in thetemperature, the energy density, and the comovingentropy of the corresponding universe.

Full causal bulk-viscous cosmological models

New exact solutions of the gravitational field equations for a homogeneous flat Friedmann–Robertson–Walker Universe filled with a causal bulk-viscous fluid with a bulk viscosity coefficient proportional to the Hubble function are obtained in the framework of the full causal Israel–Stewart–Hiscock (ISH) theory. The evolution equation of the Universe is reduced to a first kind Abel-type first-order differential equation and new classes of exact solutions of the field equations are generated from some particular solutions of this equation leading to two classes of general solutions of the Einstein field equations corresponding to particular values of the parameters entering in the physical model. The obtained solutions are represented mathematically in an exact parametric form and are interpreted physically as describing cosmological particle production. The evolution of the temperature, entropy, deceleration parameter, and bulk viscosity coefficient is also considered for each model.

Exact Causal Viscous Cosmologies

The general exact solution of the gravitational field equations for a homogeneous flat Friedmann-Robertson-Walker universe filled with a causal bulk viscous fluid with bulk viscosity coefficient proportional to the Hubble function is obtained in the framework of the full causal Israel-Stewart-Hiscock theory. The general solution of the field equations is represented in an exact closed parametric form and corresponds to a transition between two Minkowskian space-times connected by an inflationary period. The evolution of the temperature, entropy, deceleration parameter and bulk viscosity coefficient are considered in the general case. Particular solutions corresponding to a particular choice of parameters and leading to a non-inflationary evolution of the universe are presented too.