Varying Deceleration Parameter Research Articles

Exploration of bulk viscous Bianchi type cosmological model in f(T) theory of gravity

In the present paper, the expansion of Locally Rotational Symmetric (LRS) Bianchi type - I cosmological model have been investigated with Bulk Viscous matter in the context of f(T) theory of gravity, where T signifies the torsion scalar. The power model, exponential model and linear functional model of the universe have been discussed for choices of f(T)with utilization of the special form of time dependent varying deceleration parameter. The discussion involves the examination of the dynamical behaviour of these models using some dynamical parameters and its graphical representation.

Significance of a quadratically varying deceleration parameter in scalar field-dominated model and cosmic acceleration

In this study, we explore the enigma of late-time cosmic acceleration in the framework of a general scalar field playing the role of dark energy. Our investigation yields an exact solution to Einstein’s field equations, achieved through a parametrization of the deceleration parameter [Formula: see text] in quadratic form in the homogeneous and isotropic background geometry represented by Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime. This parametrization unveils a seamless transition from a decelerated to an accelerated phase in the cosmic evolution. Furthermore, we leverage this parametrization to reconstruct cosmological parameters with respect to redshift z, elucidating their dependency on certain model parameters that govern the universe’s evolutionary trajectory. The model parameters are subsequently constrained using diverse observational datasets. We provide a comprehensive analysis of the evolution of geometrical and physical parameters, complete with the numerically constrained values. To gain deeper insights into the nature of dark energy, we employ Statefinder diagnostics, conducting a thorough examination. Our findings shed light on the intricate interplay between cosmic acceleration, quintessential dark energy and the parametrization of deceleration parameter, offering valuable insights into the fundamental dynamics of the universe.

Cosmic acceleration & deceleration with f(R,T) gravity

This study includes the cosmic evolution and the potential periodicity of the universe. It employs a periodic varying deceleration parameter (PVDP) within the framework of [Formula: see text] theory of gravity, with a specific focus on the Bianchi-II model. We explore the dynamic nature of the universe, with physical and geometrical properties within this theoretical framework. We have also analyzed the cosmographic parameters, including jerk, snap, and lerk, for deeper insights into the universe’s evolution and behavior. Utilizing state finder diagrams and the Om diagnostic (which illustrates the variation of [Formula: see text] with redshift) signifying a shift from matter dominance to a stronger influence of dark energy (DE), we construct a comprehensive map of the universe’s trajectory and behavior. By employing the Bianchi-II model within the [Formula: see text] theory, our proposed model helps us in understanding the universe’s oscillatory patterns and underlying mechanisms. This research significantly contributes to our understanding of cosmic evolution and periodicity within the [Formula: see text] theory.

Anisotropic behavior of universe in f(R,Lm)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(R, L_m)$$\\end{document} gravity with varying deceleration parameter

In this research study, we investigate the anisotropic behavior of the Universe using the framework of f(R,Lm)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(R, L_m)$$\\end{document} gravity. This modified gravity theory, represented by f(R,Lm)=R2+Lmα+β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(R, L_m)=\\frac{R}{2}+L^\\alpha _m+\\beta $$\\end{document}, incorporates both the Ricci scalar (R) and matter Lagrangian density (Lm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$L_m$$\\end{document}). Our exploration centers around understanding the Universe’s dynamics through the variable deceleration parameter. Additionally, we employ energy conditions, the jerk parameter, equation-of-state (EoS) parameter and statefinder parameters as analytical tools to gain insights into the evolution of the Universe within this modified gravity scenario. Our findings are then compared to recent observational data and are found to be in agreement with the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM model. This research contributes valuable insights into the anisotropic nature of the Universe in the context of f(R,Lm)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(R, L_m)$$\\end{document} gravity and highlights its deviations from the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM model, providing a deeper understanding of the fundamental dynamics of our cosmic evolution.

FLRW universe in Weyl type f(Q,T) gravity with variable q

In this paper, we study an isotropic and homogeneous Friedmann–Lemaitre–Robertson–Walker cosmological model in Weyl type [Formula: see text] gravity with a dynamic deceleration parameter. The solution of the field equations is found using a variable deceleration parameter, viz., [Formula: see text], with q the deceleration parameter, n and m constants, and H the Hubble parameter [Tiwari et al., Eur. Phys. J. Plus 132, 1 (2017)]. Then we calculate the values of the model parameters that are most likely to accord with the most recent observational data sets. We make use of the 57 CC points, SN and BAO datasets. We have contracted a graphical representation of the dynamical behavior of the cosmological parameters (the Hubble parameter, the deceleration parameter, the energy density and the equation of state) in terms of the redshift. To investigate the various eras of the universe, the evolution of the statefinder trajectory pairs [Formula: see text] and [Formula: see text] are studied. It is shown that the main energy component of the model is ordinary matter, which behaves initially as the SCDM model and then later as a fluid resembling quintessence, which behaves as the well-known [Formula: see text]CDM model. A suitable cosmological model is constructed after analyzing the physical parameters of the model, the [Formula: see text] diagnostic analysis.

Generalized linearly varying deceleration parameter solutions of higher dimensional universe in f(R,T) theory

In this paper, generalized Friedmann–Robertson–Walker universe for Strange Quark Matter (SQM) and Normal Matter (NM) coupled with Domain Wall (DW) in form perfect fluid have been investigated in [Formula: see text] modified theory. [Formula: see text] function has been assumed as [Formula: see text] and Modified Field Equations (MEFEs) have been attained. The MEFEs of the constructed model do not allow solutions of open and closed FRW universe. Obtained modified field equations of higher dimensional flat FRW universe have been solved by using Linearly Varying Deceleration Parameter (LVDP) suggested by Akarsu and Dereli [Int. J. Theor. Phys. 51, 612 (2012)]. Pressure and energy density of the matter distributions for the Linearly Expansion Model (LEM) and Constant Expansion Model (CEM) have been attained as decreasing values by the cosmic time t and constant [Formula: see text] in [Formula: see text] gravity. But for the Exponential Expansion Model (XEM), these quantities have been obtained as time-independent. It is found out that the domain wall behaves like invisible matter when [Formula: see text] due to negative domain wall tension ([Formula: see text]) for SQM with DW of LEM. Strange quark matters for LDW and CDW models behave like cold dark matter when [Formula: see text] and [Formula: see text], respectively. One can say that SQM with DW for LEM and CEM may cause the expansion of the universe in these special situations. Also, solutions of XEM have shown that domain wall matter behaves like stiff matter when [Formula: see text]. All solutions of the constructed model in [Formula: see text] theory have been reduced to General Relativity (GR) theory solutions by assuming [Formula: see text]. Finally, all solutions obtained have been discussed in detail.

Cosmological model in f(R, T) theory with time-varying FLVDP

In this communication, we have explored spatially homogeneous, anisotropic Bianchi-II space-time in f(R, T) theory of gravity. Here, we have obtained an explicit solution of the field equations of f(R, T) theory with time dependent fractional linear varying deceleration parameter (FLVDP) i.e. q(t). The accelerating expanding nature of the cosmos has been also discussed under the suitable assumption , here α > 0. It is observed that the universe was originated from a singularity in the past and is expanding at an accelerating rate. The FLVDP depicts a transitional phase i.e., early deceleration to the current accelerating phase.

Modeling cosmic acceleration with a generalized varying deceleration parameter

Understanding the accelerating expansion of the Universe remains a fundamental challenge in modern cosmology. In this paper, we investigate a cosmological model parametrized by a generalized variable deceleration parameter to elucidate the dynamics driving cosmic acceleration. By employing constraints from the latest observational datasets, including Cosmic Chronometers (CC), Type Ia Supernovae (SNe), and Baryon Acoustic Oscillations (BAO), we assess the compatibility of the model with observational data. The chosen parametrization aligns with thermodynamic constraints on the deceleration parameter, further validating its reliability. Further, we estimate the present value of the Hubble parameter, transition redshift, deceleration parameter, and EoS parameter, which align with observational data. Lastly, our stability analysis confirms the model’s stability against small perturbations.

Observational Constraints on Hybrid Scale Factor in f(Q,T)$f(Q,T)$ Gravity with Anisotropic Space‐Time

AbstractThis paper presents an accelerating cosmological model by constraining the free parameters using the cosmological datasets in an extended symmetric teleparallel gravity for the flat and anisotropic space‐time. It employs a time variable deceleration parameter that behaves early deceleration and late time acceleration in the form of a hybrid scale factor (HSF). It obtains the present values of deceleration parameter and analyzes the late time behavior of the Universe based on the best‐fit values of the free parameters. It derives the dynamical parameters of the model and obtains the equation of state parameter at present in the quintessence region; however, at late time it approaches to ΛCDM. The energy conditions are also analyzed to validate the modified gravity and it finds that the strong energy condition is violating. It establishes the importance of a hybrid scale factor in the late time cosmic phenomena issue.

Behaviour of Bianchi Type-V Dark Energy Model in f(R,T) Gravity with a Specific Form of Hubble Parameter

Abstract: In this paper, we have constructed a Bianchi type V cosmological model, in the presence of bulk viscous fluid and within the framework of f(R,T) theory of gravity with an appropriate choice of the functional f(R,T)in the form f(R,T )=R+2f(T), where R and T are respectively Ricci scalar and trace of energy momentum tensor. In order to obtain a deterministic solution, we have considered two general forms of hyperbolic scale factors. The different forms of scale factors considered here produce time-varying deceleration parameters in all the cases that simulate the cosmic transition. The state finder diagnostic pair is found to be in the acceptable range. The physical parameters are constrained from different representative values to build up a realistic cosmological model aligned with the observational behaviour. Keywords: Bianchi type V, Dark energy, f(R,T) gravity, Variable deceleration parameter.

Role of constant jerk parameter in f(R,T) gravity

In this study, a homogeneous and anisotropic Bianchi type-I universe model is considered taking the cosmological constant as a variable in the context of f (R, T) gravity. The presented model relies on a unique condition of constant jerk parameter as j = 1, which corresponds to a flat [Formula: see text]CDM model that leads to a variable deceleration parameter. The exact solution of the field equations is obtained under that condition, and the physical and geometrical features of the model are discussed through the paper. The model has been shown to be successful in explaining recent cosmological observations such as the universe’s expansion decelerates in the early universe and accelerates in the late universe, in agreement with their current data.

Anisotropic cloud string cosmological model with five-dimensional kaluza-klein space-time

Anisotropic cloud string cosmological models has been investigated in the context of five dimensional Kaluza- Klein space time. In this paper the energy momentum tensor is generated by rest energy density and tension density of the string with particle density attached to them. To obtained the exact solutions of the Einstein field equations we assumed a scale factor a(t)=e1β2βt+c where β and c are positive constant, which yields a variable deceleration parameter (DP) q=−aäȧ2=βH+α. The physical and geometrical behavior of the models is also discussed in detail.

Marder space-time with Tsallis holographic dark energy

This present communication is an outcome of the investigation on newly proposed holographic dark energy model such as the Tsallis holographic dark energy (THDE) with Hubble horizon cutoff regarded as IR cutoff (infrared cutoff) for a spatially homogeneous and anisotropic Marder space-time in the framework of general relativity theory (GRT). Here, we have constructed the THDE models with Hubble horizon cutoff in three different ways, based on the following possibilities: (i) a varying deceleration parameter proposed by Mishra et al., (ii) hybrid expansion law (HEL) proposed by Akarsu et al. and (iii) a linearly varying deceleration parameter (LVDP) given by Akarsu and Dereli. The rapid expansion of the cosmos is thus justified for obtained models through the deceleration parameter (DP). In this way, the equation of state (EoS) parameter ([Formula: see text]) of the models describe the phantom and quintessence phases of the cosmos. Also, we compare the cosmological parameters of the obtained models with the parameters of [Formula: see text]CDM model, which indicates that the models-I and II are nearly identical to the [Formula: see text]CDM model.

Study of Frw Type Kaluza-Klein Domain Wall Cosmological Models in the Presence of Massive Scalar Field in a Modified Gravity

This article examines the physical behaviour of the Kaluza-Klein FRW type space-time with f(R,T) gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011) in the presence of a massive scalar meson field. Here, ”R” stands for the Ricci tensor, while ”T” stands for the energy-momentum tensor’s trace. We employed the (i ) hybrid expansion law (Akarsu et al. JCAP, 01:022, 2014), (ii ) the variable deceleration parameter (Mishra et al. Int. J. Theor. Phys. 52:2546, 2013), and (iii ) the linearly varying deceleration parameter (Akarsu and Dereli. Int. J. Theor. Phys. 51:612, 2012) to solve the field equations. Additionally, we looked at some of the model’s physical and kinematic characteristics. Our models have been found to show a smooth transition from the universe’s early slowdown to its current acceleration, and the current value of the deceleration parameter is found to be reasonably consistent with the observational data. The early stages of the universe’s evolution will be better understood through the study of domain wall cosmological models.

Behaviour of Magnetized Strange Quark Matter in f(R,T) Theory for General Kantowski-Sachs Model

In this study, we have investigated the behavior of magnetized strange quark matter (MSQM) in f(R,T) gravity for LRS Bianchi I, Bianchi III and Kantowski-Sachs (GKS) universe models with cosmological term. For the solutions of modified field equations, we have used linearly varying deceleration parameter (LVDP), anisotropy parameter and equation of state for strange quark matter. When the models goes to the isotropy magnetic field only occurs in Bianchi III and Kantowski-Sachs universe models. When t→∞, strange quark matter distribution behaves like dark energy. The K(θ) parameter, which allows us to obtain different universe models, is effective on the magnetic field, cosmological term and f(R,T) function. In addition, the graphics of the obtained results were examined in detail.

LRS Bianchi type-I cosmological models with periodic time varying deceleration parameter in f(R,T) gravity

In this research, we examine a spatially homogeneous anisotropic locally rotationally symmetric (LRS) Bianchi type-I cosmological model in [Formula: see text] gravity, for some choices of the function [Formula: see text] (arXiv:1104.2669 [gr-qc]). The precise solutions of the field equations are introduced for the periodic-time varying deceleration parameter that can adjust to meet the [Formula: see text]CDM model. We have reviewed the physical and dynamic characteristics of these models to understand the accelerated expansion of the Universe in the current era. Furthermore, SNe Ia union data (arXiv:0811.2379 [astro-ph]), SN Ia with BAO and CMB observations (arXiv:1203.3213 [astro-ph.CO]) and OHD[Formula: see text]JLA data (arXiv:1711.03437 [astro-ph.CO]) are used to estimate the statefinder diagnostics to get the geometric dynamics of the Universe at distinct stages and also to find the luminosity distance, angular-diameter distance, and distance modulus. We have also investigated the transit points for the deceleration parameter (q) in the framework of these three observations within the range of redshift [Formula: see text].

Bi-Quadratic Varying Deceleration Parameter to Study the Cosmological Model

This paper investigates a cosmological model employing a four-degree function of cosmic time t in the f(R, T) gravity theory using an extended form of deceleration parameter. Under the constraints of flat, diagonal, and Bianchi type-1 metrics, we develop the exact solution of Einstein field equations (EFE). We research early time deceleration and accomplish the definite solution of EFE using an extended form of deceleration parameter, as well as the always super-exponential expansion behaviour of bi-quadratically variable deceleration parameter using a graph. We explore the model’s efficacy by examining the relationship between the deceleration parameter and red shift, which offers a valid result concerning the FRW metric’s consistent homogeneous structure in light of recent cosmological observations.

Non-minimally coupled transit cosmology in f(R, T) gravity

A non-minimally coupled cosmological model is studied in [Formula: see text] gravity for a particular choice of the function in the background of flat Friedmann–Robertson–Walker universe. The modified field equations are solved with the help of a varying deceleration parameter. The time evolution of the model is analyzed for both the dynamic and kinematic quantities. For testing the viability of the results, energy conditions and the statefinder diagnostic are used. It has been shown that this model, which we discussed to examine the phase transition in the expansion of the universe, is compatible with current astrophysical observations, and that the DE model dominating the early universe is Chaplygin gas, while the model dominating the late universe is quintessence.

Cosmological parameters in Barrow holographic dark energy

This work is dedicated to the cosmological scenario of the Barrow holographic dark energy (BHDE) in the light of time varying deceleration parameter. We investigate the evolution of a spatially flat Friedmann–Robertson–Walker (FRW) universe filled with pressure-less dark matter and BHDE density. We analyze the evolutionary history of essential cosmological parameters, including the deceleration parameter, the equation of state parameter, and the density parameter, using the Hubble horizon as the IR cut-off, and find appropriate characteristics in the BHDE model. Also, we examine the various structures of the model by reconstructing the scalar field potential to describe the universe accelerated expansion phase. For more accuracy of the dark energy model characteristics, we include the statefinder pair (r,s) which mimics the [Formula: see text]CDM model.

Particle creation and Big Rip cosmological model in Lyra geometry

The current paper is concerned with the universe evolution behavior within the framework of Lyra’s geometry. The modified Einstein’s field equations based on this geometry are solved under a specific creation function and a linearly varying deceleration parameter. The energy conditions are also discussed.