Chiral Cosmological Model Research Articles

New method of exponential potentials reconstruction based on given scale factor in phantonical two-field models

We investigate two-field cosmological model with phantom and canonical fields (phantonical model as a generalisation of the quintom model for global universe evolution, including early inflationary stage). The model is represented as the chiral cosmological model with the target space conformal to 2D pseudo-Euclidean space. We found three sorts of exact solutions for a constant potential by direct integration of dynamic equations and proposed new method of exact solution construction also extended for e-folds N-formalism for the case of non-constant exponential potential. We show that the exact solutions of cosmological dynamic equations can be obtained in explicit form for any type of scale factor evolution a(t) which implies the explicit inverse dependence t = t(a), considering the quasi de Sitter expansion of the universe with non-negligible kinetic energies of scalar fields and showing that the appeared effective cosmological constant can be considered as the source of second accelerated expansion of the universe. Further we analyze cosmological perturbations in the two-field model under consideration reducing it to the single field one. Such transition give us the way of cosmological parameters calculation and comparison them to observational data. We find that in proposed two-field cosmological model the isocurvature perturbations are negligible, and observable curvature perturbations are induced by adiabatic modes only. The series of phantonical models based on exact inflationary solutions are represented, and it is shown the correspondence to observational data for these models.

Crossing the phantom divide line as an effect of quantum transitions

We consider the chiral cosmological model consisting of two scalar fields minimally coupled to gravity. In the context of a Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime, and for massless fields in the presence of a cosmological constant, we present the general solution of the field equations. The minisuperspace configuration that possesses maximal symmetry leads to scenarios which—depending on the admissible value of the parameters—correspond to a quintessence, quintom or phantom case. The canonical quantization of the model retrieves this distinction as different families of quantum states. The crossing of the phantom line is related to the existence of free or bound states for the Casimir operator of the symmetry algebra of the fields. The classical singularity, which is present in the quintessence solution, is also resolved at the quantum level.

Qualitative Analysis of the Dynamics of a Two-Component Chiral Cosmological Model

We present a qualitative analysis of chiral cosmological model (CCM) dynamics with two scalar fields in the spatially flat Friedman–Robertson–Walker Universe. The asymptotic behavior of chiral models is investigated based on the characteristics of the critical points of the selfinteraction potential and zeros of the metric components of the chiral space. The classification of critical points of CCMs is proposed. The role of zeros of the metric components of the chiral space in the asymptotic dynamics is analysed. It is shown that such zeros lead to new critical points of the corresponding dynamical systems. Examples of models with different types of zeros of metric components are represented.

Cosmological parameters of f(R) gravity with kinetic scalar curvature

We study modified f(R) gravity theory with kinetic scalar curvature reducible to chiral cosmological model of a special type. New method of cosmological parameters calculation based on reduction of two-fields model to standard one with single scalar field is proposed. Parametric correspondence to observational data is shown for massive scalar field, power-law and intermediate inflation.

Chiral Cosmological Model of f(R) Gravity with a Kinetic Curvature Scalar

We consider modified f(R) gravity with a kinetic curvature scalar, which can be reduced to a chiral cosmological model of special kind. A detailed derivation is presented for the action of a chiral cosmological model as an equivalent to a gravitational model with higher derivatives with respect to the Ricci scalar using Lagrange multipliers and a transition from the Jordan frame to the Einstein one. The equations of the model are written in the spatially flat Friedmann-Robertson-Walker metric on the basis of the constructed chiral cosmological model. Examples of solutions are found, corresponding to a special choice of the field χ = χ* = const, and its fixed value $$\chi_0=-\sqrt{3/2}\;\text{ln}2$$ . For this value of χ0, in the case of the canonical inclusion of the kinetic component of the Ricci scalar, we have obtained a nonlinear second-order differential equation with respect to H, which is not amenable to analytic solution. Therefore we implement a transition to a noncanonical form of the kinetic term. Using a fixed value of χ0, an exact solution is obtained for power-law inflation. We have considered a transition from the de Sitter and power-law solutions specified in the Jordan frame to the Einstein frame for comparison with the results obtained in f(R) gravity with higher derivatives. It is proved that there is a Weyl conformal transformation which transforms the de Sitter and power-law solutions in one frame to similar solutions in the other.

Two-Field Cosmological Models with a Second Accelerated Expansion of the Universe

The purpose of this paper is to consider cosmological models that contain two scalar fields. One field is inflaton, the other is the source of the observed accelerated expansion of universe at the present time. For the model that is considered in this work the corresponding chiral cosmological model was found and the metric of the space of the internal field is defined.

New exact solutions for a chiral cosmological model in 5D EGB gravity

We consider a chiral cosmological model in the framework of Einstein-Gauss-Bonnet cosmology. Using a decomposition of the latter equations in such a way that the first chiral field is responsible for the Einstein part of the model, while the second field together with the kinetic interaction is connected with the Gauss--Bonnet part of the theory, we find new exact solutions for the 2-component chiral cosmological model with and without the kinetic interaction between fields.

σCDM coupled to radiation: Dark energy and Universe acceleration

Recently, the Chiral Cosmological Model (CCM) coupled to cold dark matter (CDM) has been investigated as [Formula: see text]CDM model to study the observed accelerated expansion of the Universe. Dark sector fields (as Dark Energy content) coupled to cosmic dust were considered as the source of Einstein gravity in Friedmann–Robertson–Walker (FRW) cosmology. Such model had a beginning at the matter-dominated era. The purposes of our present investigation are two-fold: To extend “life” of the [Formula: see text]CDM for earlier times to radiation-dominated era and to take into account variation of the exponential potential [Formula: see text] via variation of the interaction parameter [Formula: see text]. We use Markov Chain Monte Carlo (MCMC) procedure to investigate possible values of initial conditions constrained by the measured amount of the dark matter, dark energy and radiation component today. Our analysis includes dark energy contribution to critical density, the ratio of the kinetic and potential energies, deceleration parameter, effective equation of state (EoS) and evolution of DE EoS with variation of coupling constant [Formula: see text]. A comparison with the [Formula: see text]CDM model was performed. A new feature of the model is the existence of some values of potential coupling constant, leading to a [Formula: see text]CDM solution without transition into accelerated expansion epoch.

Exact Inflationary Solutions Inspired by the Emergent Universe Scenario

We present new classes of exact inflationary solutions for a two-component chiral cosmological model with phantom and canonical scalar fields. These solutions are obtained by use of the scale factor in the form corresponding to that exploited in the emergent universe scenario. We outline in detail the method of deriving exact solutions and discuss the potential and kinetic interaction for the model.

Emergent universe supported by chiral cosmological fields in 5D Einstein-Gauss-Bonnet gravity

We propose the application of the chiral cosmological model (CCM) for the Einstein--Gauss--Bonnet (EGB) theory of gravitation with the aim of finding new models of the Emergent Universe (EmU) scenario. We analysed the EmU supported by two chiral cosmological fields for a spatially flat universe, while we have used three chiral fields when we investigated open and closed universes. To prove the validity of the EmU scenario we fixed the scale factor and found the exact solution by decomposition of EGB equations and solving the chiral field dynamics equation. To this end, we suggested the decomposition of the EGB equations in such a way that the first chiral field is responsible for the Einstein part of the model, while the second field, together with kinetic interaction term, is connected with the Gauss--Bonnet part of the theory. We proved that both fields are phantom ones under this decomposition, and that the model has a solution if the kinetic interaction between the fields equals a constant. We have presented the exact solution in terms of cosmic time. This was done for a spatially flat universe. In the case of open and closed universes we introduced the third chiral field (canonical for closed and phantom for open universe) which is responsible for the EGB and curvature parts. The solution of the third field equation is obtained in quadratures. Thus we have proved that the CCM is able to support EmU scenario in EGB gravity for spatially flat, open and closed universes.

An Emergent Universe with Dark Sector Fields in a Chiral Cosmological Model

We consider the emergent universe scenario supported by a chiral cosmological model with two interacting dark sector fields: phantom and canonical. We investigate the general properties of the evolution of the kinetic and potential energies as well as the development of the equation of state with time. We present three models based on asymptotic solutions and investigate the phantom part of the potential and chiral metric components. The exact solution corresponding to a global emergent universe scenario, starting from the infinite past and evolving to the infinite future, has been obtained for the first time for a chiral cosmological model. The behavior of the chiral metric components responsible for the kinetic interaction between the phantom and canonical scalar fields has been analyzed as well.

Chiral Cosmological Models: Dark Sector Fields Description

The present review is devoted to a Chiral Cosmological Model as the self-gravitating nonlinear sigma model with the potential of (self)interactions employed in cosmology. The chiral cosmological model has successive applications in descriptions of the inflationary epoch of the Universe evolution; the present accelerated expansion of the Universe also can be described by the chiral fields multiplet as the dark energy in wide sense. To be more illustrative we are often addressed to the two-component chiral cosmological model. Namely, the two-component chiral cosmological model describing the phantom field with interaction to a canonical scalar field is analyzed in details. New generalized model of quintom character is proposed and exact solutions are founded out. In the review we represented the perturbation theory for chiral cosmological model with the aim to describe the structure formation using the progress achieved in the inflation theory. It was shown that cosmological perturbations from chiral fields can be decomposed for inflaton and the dark sector perturbations. The two-component model is investigated in details, the general solution for shortwave approximation is obtained and analyzed for power law Universe expansion. New issue for understanding the features of Universe evolution is proposed by consideration of the dark sector fields on the inflaton background. The results are illustrated for the solutions in the long-wave approximation.

UNIFIED DARK MATTER AND DARK ENERGY DESCRIPTION IN A CHIRAL COSMOLOGICAL MODEL

We show the way of dark matter and dark energy presentation via ansatzs on the kinetic energies of the fields in the two-component chiral cosmological model (CCM). To connect a kinetic interaction of dark matter and dark energy with observational data the reconstruction procedure for the chiral metric component h22 and the potential of (self-)interaction V has been developed. The reconstruction of h22 and V for the early and later inflation have been performed. The proposed model is confronted to ΛCDM model as well.

COSMOLOGICAL MODELS OF GLOBAL UNIVERSE EVOLUTION AND DECOMPOSITION OF PERTURBATIONS

It is shown that cosmological models, based on the self-interacting scalar field theory or on the theory of the chiral non-linear sigma model. Can describe the global evolution of the Universe, extending from an inflationary stage to the present time epoch. The method of cosmological perturbations decomposition for inflaton and non-inflaton ones is applied for two-component chiral cosmological model in the spatially flat Friedmann-Robertson-Walker (FRW) Universe. New non-inflaton mode of cosmological perturbations is found.