Field Cosmological Models Research Articles

Constraining hybrid potential scalar field cosmological model in Lyra’s geometry with recent observational data

In this study, we investigate a scalar field cosmological model with Lyra’s geometry to explain the present cosmic expansion in a homogeneous and isotropic flat FRW universe. In Einstein’s field equations, we presupposed a variable displacement vector as an element of Lyra’s geometry. In the context of the conventional theory of gravity, we suggest a suitable parametrization of the scalar field’s dark energy density in the hybrid function of redshift [Formula: see text], confirming the essential transition behavior of the universe from a decelerating era to the present accelerated scenario. We present constraints on model parameters using the most recent observational datasets from OHD, BAO/CMB and Pantheon, taking Markov Chain Monte Carlo (MCMC) analysis into account. For the proposed model, the best estimated values of parameters for the combined dataset (OHD, BAO/CMB and Pantheon) are [Formula: see text][Formula: see text]km/s/Mpc, [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]. The model exhibits a flipping nature, and the redshift transition occurs at [Formula: see text]. The current value of the decelerated parameter for the proposed model is calculated as [Formula: see text] for the combined dataset. Some dynamical properties of the model like energy density ([Formula: see text]), scalar field pressure ([Formula: see text]), EoS parameter of scalar field ([Formula: see text]), and effective EoS parameter ([Formula: see text]) are analyzed and presented. Further, we have also examined the statefinder diagnosis and jerk parameters of the derived model. The total density parameter for the derived model is found to be unity which is in nice agreement with recent standard findings.

Induced cosmological anisotropies and CMB anomalies by a non-abelian gauge-gravity interaction

We present a non-abelian cousin of the model presented in Lee et al. (2024) which induces cosmological anisotropies on top of standard FLRW geometry. This is in some sense doing a cosmological mean field approximation, where the mean field cosmological model under consideration would be the standard FLRW, and the induced anisotropies are small perturbative corrections on top of it. Here we mostly focus on the non-abelian SU(2) gauge fields coupled to the gravity to generate the anisotropies, which can be a viable model for the axion-like particle (ALP) dark sector. The induced anisotropies are consequences of the non-trivial back-reaction of the gauge fields on the gravity sector, and by a clever choice of the parametrization, one can generate the Bianchi model we have studied in this note. We also show that the anisotropies influence the Sachs–Wolfe effect and we discuss the implications.

Induced cosmological anisotropy by a gauge-gravity interaction

We present a simple model which generates cosmological anisotropies on top of standard FLRW geometry. This is in some sense reminiscent of the mean field approximation, where the mean field cosmological model under consideration would be the standard FLRW, and the anisotropy is a small perturbative correction on top of it. Using a supergravity-inspired model, we confirm that the stable fixed point of our model corresponds to standard FLRW cosmology. We use a Bianchi VII0-type model supplemented with a scalar and U(1) gauge fields, and we show that the anisotropies of the geometry are generated by the non-trivial interaction between the gravity sector and the U(1) gauge sector. Studying the attractor flow, we show that the anisotropies are present at early times (high redshift) and decay asymptotically to an FLRW attractor fixed point. With such a mechanism, observations of non-isotropy are not contradictory to FLRW geometry or indeed the ΛCDM model. Such models could in principle shed some insights on the present cosmological tensions.

Observation constraints on scalar field cosmological model in anisotropic universe

In this study, we have explored a scalar field cosmological model in the axially symmetric Bianchi type-I universe. In this study, our aim is to constrain the scalar field dark energy model in an anisotropic background. For this purpose, the explicit solution of the developed field equations for the model is determined and analyzed. Constraints on the cosmological model parameters are established utilizing Markov Chain Monte Carlo (MCMC) analysis and using the latest observational datasets of OHD, BAO, and Pantheon. For the combined dataset (OHD, BAO, and Pantheon), the best-fit values of Hubble and density parameters are estimated as [Formula: see text], [Formula: see text] [Formula: see text] and [Formula: see text]. The model shows a flipping nature and redshift transition occurs at [Formula: see text], and the present value of decelerated parameter is computed to be [Formula: see text] for the combined dataset. We have explored characteristics like the universe’s age, particle horizon, deceleration parameter, and jerk parameter. The dynamical properties, such as energy density [Formula: see text], scalar field pressure [Formula: see text], and equation of state parameter [Formula: see text], are analyzed and presented. We have also described the behavior of the scalar potential [Formula: see text] and scalar field. Furthermore, the authors also described the behavior of energy conditions in scalar-tensor cosmology. The scenario of the present accelerated expansion of the universe is described by the contribution of the scalar field.

Unified dark energy from Chiral-Quintom model with a mixed potential in Friedmann–Lemaître–Robertson–Walker cosmology

For a spatially Friedmann–Lemaître–Robertson–Walker cosmology, we propose a multi-scalar field gravitational model. Specifically, we consider a two-scalar field cosmological model in which the kinetic components of the scalar fields establish a two-dimensional sphere of Lorentzian signature. For our Chiral-Quintom model we choose a mixed potential term Vleft( phi ,psi right) =V_{0}e^{lambda phi }+U_{0}e^{kappa phi }psi ^{frac{1}{sigma } } and we investigate the asymptotic limits of the cosmological parameters. This model for U_{0}=0, provides a generalization of the hyperbolic inflation where the equation of the state parameter can cross the phantom divide line. When U_{0}ne 0 we observe that this cosmological model exhibits asymptotic solutions that encompass accelerated universes, big rip singularities, and dust-like solutions. Hence, this multi-scalar field model it can be regarded as as a dark energy unify model which describes a variety of asymptotic cosmological scenarios.

Dissipative quintessence and its cosmological implications

We consider a generalization of the quintessence type scalar field cosmological models, by adding a multiplicative dissipative term in the scalar field Lagrangian, which generally is represented in an exponential form. The generalized dissipative Klein-Gordon equation is obtained in a general covariant form in Riemann geometry, from the variational principle with the help of the Euler-Lagrange equations. The energy-momentum tensor of the dissipative scalar field is also obtained from the dissipative Lagrangian, and its properties are discussed in detail. Several applications of the general formalism are presented for the case of the cosmological Friedmann-Lema\^{\i}tre-Robertson-Walker metric. The generalized Friedmann equations in the presence of the dissipative scalar field are obtained for a specific form of dissipation, with the dissipation exponent represented as the time integral of the product of the Hubble function, and of a function describing the dissipative properties of the scalar field. For this case the Friedmann equations reduce to a system of differential-integral equations, which, by means of some appropriate transformation, can be represented in the redshift space as a first order dynamical system. Several cosmological models, corresponding to different choices of the dissipation function, and of the scalar field potential, are considered in detail. For the different values of the model parameters the evolution of the cosmological parameters (scale factor, Hubble function, deceleration parameter, the effective density and pressure of the scalar field, and the parameter of the dark energy equation of state, respectively) is considered in detail by using both analytical and numerical techniques. A comparison with the observational data for the Hubble function and with the predictions of the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ paradigm is presented for each dissipative scalar field model. In the large time limit the model describes an accelerating universe, with the effective negative pressure induced by the dissipative effects associated with the scalar field. Accelerated expansion in the absence of the scalar field potential is also possible, with the kinetic term dominating the expansionary evolution. The dissipative scalar field models describe well the data, with the model free parameters obtained by a trial and error method. The obtained results show the dissipative scalar field model offers an effective dynamical possibility for replacing the cosmological constant and for explaining the recent cosmological observational data.

Multiscalar-torsion cosmology: exact and analytic solutions from noether symmetries

The Noether symmetry analysis is applied in a multiscalar field cosmological model in teleparallel gravity. In particular, we consider two scalar fields with interaction in scalar-torsion theory. The field equations have a minisuperspace description, and the evolution of the physical variables depends on the potential function that drives the scalar fields’ dynamics. With the requirement for the field equations to admit non-trivial Noether point symmetries and the use of the first theorem of Noether, we constrain all the functional forms for the potential. Finally, we apply symmetry vectors and the corresponding conservation laws to determine exact and analytic solutions in multiscalar-torsion cosmology.

Reconstruction of [formula omitted] gravity in homogeneous backgrounds and a general prescription for reconstructing through scalar field

A technique for the reconstruction of the potential for a scalar field in cosmological models based on induced gravity has recently been developed by Alexander Y. Kamenshchik, Alessandro Tronconi, and Giovanni Venturi (Kamenshchik et al., 2011). In this paper, this extended reconstruction method is utilized to investigate the nature of the scalar potentials of the most extended action of F(T)-gravity context. First, a general formalism is formulated and then it is utilized for considering some well-known special cases including ‘Barotropic Fluid’, ‘Cosmological Constant’, and ‘Modified Chaplygin Gas’.The analysis of the results is carried out by the use of the B-function method which has recently been suggested by the author (Tajahmad, 2020).As we know, assuming a proportional relation between the scale factor of the x-direction and the scale factors of y and z directions (i.e. A=Bm) in dealing with LRS Bianchi-I background is prevalent. Pursuant to observational data, the correct physical range of m is extracted. It is demonstrated that, unlike several papers, m is very close to 1.Some interesting discussions about the modified and generalized Chaplygin gases are performed. The ranges of the amounts of free parameters of the various types of Chaplygin gases are corrected according to observational data. It is demonstrated that the generalized Chaplygin gas model namely P=−σ2/ρν may be developed as P=−σ2/ρν(t) (i.e. ν=const.⟶ν=ν(t)).Ultimately, by combining Ref. Kamenshchik et al. (2011) and the current paper, a general prescription is recommended for the reconstruction of the potentials of alternative theories of gravity (especially F(φ)R and F(T)), and their relevant analysis. Furthermore, a recurring scheme of the analysis of the results is presented for the clarification.

Creation field cosmological models for dust distribution and time-dependent cosmological term (Λ) in Bianchi type II space-time

In this paper, we present solution of Einstein field equations which admit dust distribution and negative energy massless scalar field as a source with cosmological term ([Formula: see text]) in the frame work of Bianchi type II space-time. The models satisfy conservation equation and creation field increases with time satisfying the result as investigated by Hoyle and Narlikar [A new theory of gravitation, Proc. Roy. Soc. A 282 (1964) 191]. The deceleration parameter ([Formula: see text]) for the model (22) shows a transition from decelerating to accelerating regime with creation. A comparison with other cosmological models shows a transition from decelerating to accelerating regime with and without creation is mentioned. The present model is free from singularity, particle horizon and provides a natural explanation for inflationary scenario and isotropization. These features make the creation field cosmological models theoretically superior to the Big Bang models. Creation field and Einstein field equation are derived using principle of least action and the Lagrangian formulation of variable cosmological term is derived as mentioned by Moffat [Lagrangian formulation of a solution to the cosmological constant problem (1996), arXiv:astro-ph/9608202v1]. The current creation rate with other physical consequences is also discussed. For illustrative purposes, evolutionary behaviors of some cosmological parameters are shown graphically. In the figures, the cosmic time [Formula: see text] is given in gravitational units assuming the velocity of light [Formula: see text]. This [Formula: see text] and [Formula: see text]. Therefore, by multiplying cosmic time [Formula: see text] by (light years)−1, we obtain the coordinate time in years.

Quantum cosmology for double scalar field cosmological model: Symmetry analysis

The present cosmological model consists of two scalar fields which are minimally coupled to gravity and having a mixed kinetic term. In the background of homogeneous and isotropic FLRW space–time the present model is characterized by the coupling function and the potential function which are functions of one of the scalar fields. Using symmetries of the 3D augmented space, homothetic and killing vectors are determined. Finally, quantum cosmology has been formulated for the present model and the wave function of the universe has been evaluated.

Nonlinear Spinor Field in Cosmological Models Without Singularity and Without the Beginning of Time

Nonlinear Spinor Field in Cosmological Models Without Singularity and Without the Beginning of Time

Singularities in Inflationary Cosmological Models

Due to the accelerated expansion of the universe, the possibilities for the formation of singularities has changed from the classical Big Bang and Big Crunch singularities to include a number of new scenarios. In recent papers it has been shown that such singularities may appear in inflationary cosmological models with a fractional power scalar field potential. In this paper we enlarge the analysis of singularities in scalar field cosmological models by the use of generalised power expansions of their Hubble scalars and their scalar fields in order to describe all possible models leading to a singularity, finding other possible cases. Unless a negative scalar field potential is considered, all singularities are weak and of type IV.

Multi-scalar field cosmological model and possible solutions using Noether symmetry approach

In this work, a cosmological model is considered having two scalar fields minimally coupled to gravity with a mixed kinetic term. The model is characterized by the coupling function and the potential function which are assumed to depend on one of the scalar fields. Instead of choosing these functions phenomenologically here, they are evaluated assuming the existence of Noether symmetry. By appropriate choice of a point transformation in the augmented space, one of the variables in the Lagrangian becomes cyclic and the evolution equations become much simpler to have solutions. Finally, the solutions are analyzed from cosmological view point.

Dynamical system analysis of self-interacting three-form field cosmological model: stability and bifurcation

The present work deals with Cosmological model of a three-form field, minimally coupled to gravity and interacting with cold dark matter in the background of flat FLRW space-time. By suitable choice of the dimensionless variables, the evolution equations are converted to an autonomous system and cosmological study is done by dynamical system analysis. The critical points are determined and the stability of the (non-hyperbolic) equilibrium points are examined by center manifold Theory. Possible bifurcation scenarios have been examined by the Poincaré index theory to identify possible cosmological phase transition. Also stabilities of the critical points have been analyzed globally using geometric features.

Dynamics of a two scalar field cosmological model with phantom terms

We perform a detailed analysis of the dynamics of a chiral-like cosmological model where the scalar fields can have negative kinetic terms. In particular, we study the asymptotic dynamics for the gravitational field equations for four different models in a spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) background space. When one of the scalar fields is phantom, we show that the cosmological fluid can evolves such that the parameter of the equation of state crosses twice the phantom divide line without the appearance of ghosts. Moreover, the cosmological viability of these four models is discussed.

Integrability and cosmological solutions in Einstein-\xe6ther-Weyl theory

We consider a Lorentz violating scalar field cosmological model given by the modified Einstein-æther theory defined in Weyl integrable geometry. The existence of exact and analytic solutions is investigated for the case of a spatially flat Friedmann–Lemaître–Robertson–Walker background space. We show that the theory admits cosmological solutions of special interests. In addition, we prove that the cosmological field equations admit the Lewis invariant as a second conservation law, which indicates the integrability of the field equations.

Comment on “Brans-Dicke scalar field cosmological model in Lyra’s geometry”

In the present study, we comment on Brans-Dicke scalar field cosmological model in Lyra's geometry [Maurya \& Zia, Phys. Rev. D \textbf{100}, 023503 (2019)]. In this comment, we investigate that there is no acceleration in the model proposed by the authors of Phys. Rev. D \textbf{100}, 023503 (2019). Therefore, despite the claims to the contrary the Brans-Dicke Scalar Field Cosmological Model in Lyra's Geometry with high Brans-Dicke (BD) coupling parameter $\omega$ and constant $\beta$ can not produce late time acceleration in the universe.

Reply to “Comment on ‘Brans-Dicke scalar field cosmological model in Lyra’s geometry’ ”

The present study is a response to the raising comments on Brans-Dicke scalar field cosmological models in Lyra's geometry [A. K. Yadav, Phys. Rev. D 10, 108301 (2020)] by Dr. Anil Kumar Yadav. We have corrected the manuscripts and remove the contradictions observed by the comment author. Now, the present cosmological model is a transit phase model with Brans-Dicke coupling constant $\ensuremath{\omega}l\ensuremath{-}1.33$ while the equation of state parameter (EoS) lies in the range $0\ensuremath{\le}\ensuremath{\gamma}l0.33$. The Brans-Dicke scalar field is responsible candidate for the acceleration in expansion of the universe.

Proceedings 9th International Conference on Quantum Simulation and Quantum Walks

This volume contains a selection of papers presented at the 9th in a series of international conferences on Quantum Simulation and Quantum Walks (QSQW). During this event, we worked on the development of theories based upon quantum walks and quantum simulation models, in order to solve interrelated problems concerning the simulation of standard quantum field theory, quantum gravity and cosmological models, dissipative quantum computing, searching on complex quantum networks, and the topological classification of multi-particle quantum walks.

Extended analysis for the evolution of the cosmological history in Einstein-aether scalar field theory

We consider an Einstein-aether scalar field cosmological model where the aether and the scalar field are interacting. The model of our consideration consists the two different interacting models proposed in the literature by Kanno et al. and by Donnelly et al. We perform an extended analysis for the cosmological evolution as it is provided by the field equations by using methods from dynamical systems; specifically, we determine the stationary points and we perform the stability analysis of those exact solutions.