QUALITATIVE-ANALYSIS OF CAUSAL ANISOTROPIC VISCOUS-FLUID COSMOLOGICALMODELS

The truncated Israel-Stewart theory of irreversible thermodynamics is used to describe the bulk viscous pressure and the anisotropic stress in a class of spatially homogeneous viscous-fluid cosmological models. The governing system of differential equations is written in terms of dimensionless variables and a set of dimensionless equations of state is utilized to complete the system, The resulting dynamical system is then analysed using standard geometric techniques, It is found that t he presence of anisotropic Stress plays a dominant role in the evoluti on of the anisotropic models. In particular, in the case of the Bianch i type-I models it is found that anisotropic stress leads to models th at violate the weak energy condition and to the creation of a periodic orbit in some instances. The stability of the isotropic singular poin ts is analysed in the case with zero heat conduction; it is found that there are ranges of parameter values such that there exists an attrac ting isotropic Friedmann-Robertson-Walker model. In the case of zero a nisotropic stress but, with non-zero heat conduction, the stability of the singular points is found to be the same as in the corresponding c ase with zero heat conduction; hence the presence of heat conduction d oes not apparently affect the global dynamics of the model.