Barotropic Matter Research Articles

Constraining unified dark matter models with weak lensing

We study the dynamics of a non-minimally coupled scalar field cosmology with a potential function. We use the framework of dynamical systems theory to investigate all evolutional paths admissible for all initial conditions. Additionally, we assume the presence of barotropic matter and show that the dynamics can be formulated in terms of an autonomous dynamical system. We have found fixed points corresponding to three main stages of the evolution of the universe, namely, radiation, matter and quintessence domination epochs. Using the linearization of the dynamical systems in the vicinity of the critical points we explicitly obtain formulas determining the effective equation of state parameter for the universe at different epochs. In our approach the form of w(z) parametrisation is derived directly from the dynamical equations rather than postulated a priori.

Remarks on (super-)accelerating cosmological models in general scalar–tensor gravity

We consider Friedmann-Lemaitre-Robertson-Walker cosmological models in the framework of general scalar-tensor theories of gravity (STG) with arbitrary coupling functions, set in the Jordan frame. First we describe the general properties of the phase space in the case of barotropic matter fluid and scalar field potential for any spatial curvature (flat, spherical, hyperbolic). Then we address the question under which conditions epochs of accelerated and super-accelerated expansion are possible in STG. For flat models filled with dust matter (and vanishing potential) we give a necessary condition on the coupling function of the scalar field which must be satisfied to allow acceleration and super-acceleration. This is illustrated by a specific example.

NON-COMMUTATIVE BIANCHI QUANTUM COSMOLOGY

Introducing non-commutative variables in the minisuperspace, we obtain the non-commutative quantum solutions to the Wheeler–DeWitt equation with an arbitrary factor ordering, for the anisotropic Bianchi type I cosmological model, coupled to barotropic matter and cosmological term Λ. From the probability density, the inclusion of non-commutativity seems to retard the isotropization of the universe.

Integrability of anisotropic and homogeneous Universes in scalar-tensor theory of gravitation**In this paper, Greek indices run from 0 to 4, Latin indices run from 1 to 3 and ∇μ indicates a covariant derivative.

In this paper, we develop a method based on the analysis of the Kovalewski exponents to study the integrability of anisotropic and homogeneous Universes. The formalism is developed in scalar-tensor gravity, the general relativistic case appearing as a special case of this larger framework. Then, depending on the rationality of the Kovalewski exponents, the different models, both in the vacuum and in the presence of a barotropic matter fluid, are classified, and their integrability is discussed.

ASSISTED INFLATION

The dynamical properties of spatially homogeneous and isotropic cosmological models containing a barotropic perfect fluid and multiple scalar fields with independent exponential potentials is investigated. It is shown that the assisted inflationary scaling solution is the global late-time attractor for the parameter values for which the model is inflationary, even when curvature and barotropic matter are included. For all other parameter values the multi-field curvature scaling solution is the global late-time attractor (in these solutions the curvature is not dynamically negligible asymptotically). Consequently, in general all of the scalar fields in multi-field models with exponential potentials are non-negligible in late-time behaviour, contrary to what is commonly believed.

Dynamics of multi-scalar-field cosmological models and assisted inflation

We investigate the dynamical properties of a class of spatially homogeneous and isotropic cosmological models containing a barotropic perfect fluid and multiple scalar fields with independent exponential potentials. We show that the assisted inflationary scaling solution is the global late-time attractor for the parameter values for which the model is inflationary, even when curvature and barotropic matter are included. For all other parameter values the multi-field curvature scaling solution is the global late-time attractor (in these solutions asymptotically the curvature is not dynamically negligible). Consequently, we find that in general all of the scalar fields in multi-field models with exponential potentials are non-negligible in late-time behaviour, contrary to what is commonly believed. The early-time and intermediate behaviour of the models is also studied. In particular, n-scalar field models are investigated and the structure of the saddle equilibrium points corresponding to inflationary m-field scaling solutions and non-inflationary m-field matter scaling solutions are also studied (where m<n), leading to interesting transient dynamical behaviour with new physical scenarios of potential importance.

Stability analysis of multiple scalar field cosmologies with matter

We investigate the dynamics of a class of Robertson-Walker spacetimes containing multiple scalar fields and ordinary barotropic matter. The potentials for the scalar fields are assumed to be of an exponential form that are multiplicatively coupled. In this case the effective scalar field potential for the m scalar fields j, (1 j m), has the form Veff = j = 1m V0ekjj. We show that the power-law inflationary solution is the local attractor if j = 1m kj2 < 2. In particular, in the case of two scalar fields, we show that the power-law inflationary solution is indeed the global attractor and hence we make the argument that the power-law inflationary solution is also the global attractor in the m scalar field case. If j = 1m kj2 > 2 then we further argue that the curvature scaling solution is the global attractor for the open or negatively curved models. If j = 1m kj2 > 2 then we show that the global attractor for the flat or zero-curvature models is either a power-law solution, a matter scaling solution, or a massless scalar field solution.

Scalar field cosmologies with barotropic matter: models of Bianchi class B

We investigate in detail the qualitative behaviour of the class of Bianchi type B spatially homogeneous cosmological models in which the matter content is composed of two non-interacting components; the first component is described by a barotropic fluid having a gamma-law equation of state, whilst the second is a non-interacting scalar field with an exponential potential V() = ek. In particular, we study the asymptotic properties of the models both at early and late times, paying particular attention to whether the models isotropize (and inflate) to the future, and we discuss the genericity of the cosmological scaling solutions.