Scalar Field Cosmological Models Research Articles

Five dimensional perfect fluid coupled with massless scalar field cosmological model in GTR

Five dimensional perfect fluid coupled with massless scalar field cosmological model in GTR

An Exact Scalar Field Inflationary Cosmological Model Which Solves Cosmological Constant Problem, Dark Matter Problem and Other Problems of Inflationary Cosmology

An exact scalar field cosmological model is constructed from the exact solution of the field equations. The solutions are exact and no approximation like slow roll is used. The model gives inflation, solves horizon and flatness problems. The model also gives a satisfactory estimate of present vacuum energy density as well as vacuum energy density at Planck epoch and solves cosmological constant problem of 120 orders of magnitude discrepancy of vacuum energy density. Further, this model predicts existence of dark matter/energy and gives an extremely accurate estimate of present energy density of dark matter and energy. Along with explanations of graceful exit, radiation era, matter domination, this model also indicates the reason for present accelerated state of the universe. In this work a method is shown following which one can construct an infinite number of exact scalar field inflationary cosmological models.

N-body simulations for coupled scalar-field cosmology

We describe in detail the general methodology and numerical implementation of consistent N-body simulations for coupled scalar field cosmological models, including the background cosmology and the generation of initial conditions (with the different couplings to different matter species taken into account). We perform fully consistent simulations for a class of coupled scalar field models with an inverse power-law potential and negative coupling constant, for which the chameleon mechanism does not operate. We find that in such cosmological models the scalar-field potential plays a negligible role except in the background expansion, and the fifth force that is produced is proportional to gravity in magnitude, justifying the use of a rescaled gravitational constant G in some earlier N-body simulations of similar models. We study the effects of the scalar coupling on the nonlinear matter power spectra and compare with linear perturbation calculations to investigate where the nonlinear model deviates from the linear approximation. For the first time, the algorithm to identify gravitationally virialized matter halos is adapted to the scalar field cosmology, and then used to measure the mass function and study the properties of virialized halos. We find that the net effect of the scalar coupling helps produce more heavy halos in our simulation boxes and suppresses the inner (but not the outer) density profile of halos compared with those predicted by lambda-CDM, while this suppression weakens as the coupling between the scalar field and dark matter particles increases in strength.

Scalar-field cosmological and collapse models with general self-interaction potentials

We present the results of the investigation of a wide class of self-interacting, self-gravitating homogeneous scalar fields models, characterized by quite general conditions on the scalar field potential, and including both asymptotically polynomial and exponential behaviors. We show that the generic evolution is always divergent in a finite time, and this result is used to construct cosmological models as well as radiating collapsing star models of the Vaidya type – for the latter it turns out that black holes are generically formed.

Non-minimally coupled scalar field cosmology on the phase plane

In this publication we investigate dynamics of a flat FRW cosmological modelwith a non-minimally coupled scalar field with the coupling term ξRψ2 in the scalar field action. The quadratic potential functionV(ψ) ∝ ψ2 is assumed. All the evolutional paths are visualizedand classified in the phase plane, at which the parameter of non-minimalcoupling ξ plays the role of a control parameter. The fragility of globaldynamics with respect to changes of the coupling constant is studied in details.We find that the future big rip singularity appearing in the phantom scalarfield cosmological models can be avoided due to non-minimal coupling constanteffects. We have shown theexistence of a finite scale factor singular point (future or past) where the Hubble function as well as its first cosmological time derivative diverge.

Scalar field cosmological models with finite scale factor singularities

We construct a scalar field based cosmological model, possessing a cosmological singularity characterized by a finite value of the cosmological radius and an infinite scalar curvature. Using the methods of the qualitative theory of differential equations, we give a complete description of the cosmological evolutions in the model under consideration. There are four classes of evolutions, two of which have finite lifetimes, while the other two undergo an infinite expansion. We discuss also the relation between the dynamics of the model and the intermediate inflation phenomenology.

Exact models with non-minimal interaction between dark matter and (either phantom or quintessence) dark energy

A method for deriving Friedmann–Robertson–Walker (FRW) solutions developed in Chimento and Jakubi (1996 Int. J. Mod. Phys. D 5 71–84) is generalized to account for models with non-minimal coupling between the dark energy and the dark matter that are based on an action principle. New quintessence and phantom (flat) FRW solutions are found. Their physical significance is discussed. Additionally, the aforementioned method is modified so that, ‘coincidence-free’ solutions can be readily derived. Besides, we review some aspects of the phantom barrier crossing. In this regard we present a model which is free from the coincidence problem and, at the same time, does the crossing of the phantom barrier ω = −1 at late time. Finally, we give additional comments on the non-predictive properties of scalar-field cosmological models with or without energy transfer.

Smooth dynamical crossing of the phantom divide line of a scalar field in simple cosmological models

Simple scalar field cosmological models are considered describing gravity assisted crossing of the phantom divide line. This crossing or (de)-phantomization characterized by the change of the sign of the kinetic term of the scalar field is smooth and driven dynamically by the Einstein equations. Different cosmological scenarios, including the phantom phase of matter are sketched.