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Using the methods developed for different Bianchi class A cosmological models we treat the simplest Bianchi class B model, namely Bianchi type V. The future non-linear stability for solutions of the Einstein-Vlasov system is demonstrated and it is shown that these solutions are asymptotically stable to the Milne solution. Within the isotropic solutions of the Einstein-Vlasov system the spatially flat Friedmann solution is unstable within this class, and expanding models tend also to the Milne solution. [ABSTRACT FROM AUTHOR]

We refine the null alignment classification of the Weyl tensor of a fivedimensional spacetime. The paper focusses on the algebraically special alignment types N, III, II and D, while types I and G are briefly discussed. A first refinement is provided by the notion of spin type of the components of highest boost weight. Second, we analyze the Segre types of the Weyl operator acting on bivector space and examine the intersection with the spin type classification. We present a full treatment for types N and III, and illustrate the classification from different viewpoints (Segre type, rank, spin type) for types II and D, paying particular attention to possible nilpotence, which is a new feature of higher dimensions. We also point out other essential differences with the four-dimensional case. In passing, we exemplify the refined classification bymentioning the special subtypes associated to certain important spacetimes, such as Myers-Perry black holes, black strings, Robinson- Trautman spacetimes and purely electric/magnetic type D spacetimes. [ABSTRACT FROM AUTHOR]

We discuss the difference in views of the universe as seen by two different observers. While one of the observers follows a geodesic congruence defined by the geometry of the cosmological model, the other observer follows the fluid flow lines of a perfect fluid with a linear equation of state. We point out that the information these observers collect regarding the state of the universe can be radically different; while one observes a non-inflating, ever-expanding, ever-lasting universe, the other observer can experience a dynamical behavior reminiscent of that of quintessence or even that of a phantom cosmology leading to a "big rip" singularity within finite time (but without the need for exotic forms of matter). [ABSTRACT FROM AUTHOR]

Dynamical systems techniques are used to study the class of self-similar static spherically symmetric models with two non-interacting scalar fields with exponential potentials. The global dynamics depends on the scalar self-interaction potential parameters k[sub l] and k[sub 2]. For all values of k[sub 1], k[sub 2], there always exists (a subset of) expanding massless scalar field models that are early-time attractors and (a subset of) contracting massless scalar field models that are late-time attractors. When k[sub l] ≤ 1/v√3 and k[sub 2] ≤ l/ √3, in general the solutions evolve from an expanding massless scalar fields model and then recollapse to a contracting massless scalar fields model. When k[sub 1] < 1/ √3 or k[sub 2] < l/ √3, the solutions generically evolve away from an expanding massless scalar fields model or an expanding single scalar field model and thereafter asymptote towards a contracting massless scalar fields model or a contracting single scalar field model. It is interesting that in this case a single scalar field model can represent the early-time or late-time asymptotic dynamical state of the models. The dynamics in the physical invariant set which constitutes a part of the boundary of the five-dimensional timelike self-similar physical region are discussed in more detail. [ABSTRACT FROM AUTHOR]

We study a class of inhomogeneous and anisotropic G[sub 2] string cosmological models. In the case of separable G[sub 2] models we show that the governing equations reduce to a system of ordinary differential equations. We focus on a class of separable G[sub 2] M-theory cosmological models, and study their qualitative behavior (a class of models with time-reversed dynamics is also possible). We find that generically these inhomogeneous M-theory cosmologies evolve from a spatially inhomogeneous and negatively curved model with a nontrivial form field toward spatially flat and spatially homogeneous dilaton-moduli-vacuum solutions with trivial form fields. The late time behavior is the same as that of spatially homogeneous models previously studied. However, the inhomogeneities are not dynamically insignificant at early times in these models. [ABSTRACT FROM AUTHOR]

Presents a qualitative analysis for a class of homogeneous cosmologies derived from the string effective action when a cosmological constant is present in the matter sector of the theory. Effect of such term on the qualitative dynamics; Analytical solutions corresponding to the equilibrium points.

A new general approach for investigating imperfect fluid cosmological models is introduced in which the equations of state are completely ‘‘dimensionless.’’ Such equations of state are then utilized to reduce the Einstein field equations governing Bianchi V imperfect fluid cosmologies to a plane-autonomous system of equations, thus enabling the qualitative behavior of these cosmological models to be analyzed in a straightforward manner. The resulting plane-autonomous system is investigated. Finally, exact solutions of the Bianchi V imperfect fluid field equations in the case when the equations of state take on a particularly simple form are discussed. [ABSTRACT FROM AUTHOR]

This paper studies early universe cosmologies derived from a scalar-tensor action containing cosmological constant terms and massless fields. The governing equations can be written as a dynamical system which contains no past or future asymptotic equilibrium states (i.e., no sources nor sinks). This leads to dynamics with very interesting mathematical behavior such as the existence of heteroclinic cycles. The corresponding cosmologies have novel characteristics, including cyclical and bouncing behavior possibly indicating chaos. The connection between these early universe cosmologies and those derived from the low-energy string effective action is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]