EoS Parameter Research Articles

Observational constraints on freezing quintessence in a nonlinear f(R,Lm) gravity

In this paper, we investigate the freezing quintessence scenario in late-time cosmic expansion using a nonlinear [Formula: see text] gravity model, [Formula: see text], where [Formula: see text] is a free parameter. We consider a solution for this model using an appropriate parametrization of the scale factor, and then the model is constrained by observational datasets, including CC, Pantheon[Formula: see text] (SN), and CC[Formula: see text][Formula: see text][Formula: see text]SN[Formula: see text][Formula: see text][Formula: see text]BAO. Our analysis yields results aligning closely with observational data. The Hubble parameter, deceleration parameter, matter-energy density, and EoS parameter of our model exhibit expected trends over cosmic time, supporting its physical validity. Furthermore, the model demonstrates consistency with the [Formula: see text]CDM model in late times, displaying freezing behavior in the [Formula: see text] plane and stability against density perturbations. Our findings suggest that the modified [Formula: see text] gravity model is a credible approach to describing the universe’s accelerating phase.

Anisotropic Cosmic Expansion Inspired by Some Novel Holographic Dark Energy Models in f(Q)$f(Q)$ Theory

AbstractThe present work discusses the topic of cosmic evolution in an intriguing framework of theory of gravity (with as a non‐metricity (NM) scalar which controls the gravitational interaction) by using some recently proposed holographic dark energy (HDE) models. To achieve this goal, the dynamical equations for locally rotationally symmetric (LRS) Bianchi type‐I (BI) geometry are formulated with matter contents as a mixture of dust and anisotropic fluids. By assuming that the time‐redshift relation follows a Lambert function, the cosmological model is constructed by using Rényi HDE (RHDE), Sharma–Mittal HDE (SMHDE) and Generalized HDE (GHDE) as separate cases where Hubble horizon is taken as an infrared (IR) cutoff. Cosmological characteristics of these models are then examined through graphs of energy densities, skewness parameter , deceleration, and EoS parameters. The evolution of the EoS parameter is also studied, i.e., to discuss the dynamical characteristics of constructed DE models and assess the stability of models via the squared speed of sound parameter. It is found that the plane shows the freezing region for RHDE and GHDE models while the thawing region for the SMHDE case. Also, it is concluded that all constructed models exhibit cosmologically viable and stable behavior.

Crop Yield Mapping with ARC using only Optical Remote Sensing

Abstract. ARC is a new method to generates time series of a full set of biophysical parameters derived from optical EO. Here, we examine relationships between this ‘full’ set and maize yield. 15 Parameters per pixel are estimated over the US corn belt using ARC, to fully describe the phenology, soil, and crop status over time for typical behaviour. ARC is tested for a new model over an area of irrigated and rain-fed winter crop in South Africa. We find that care must be taken for episodic events, and robust filtering methods should be developed for ARC, but average magnitude and timing is well-expressed. We find that a robust yield model (over time and space) can be created at the county-level for maize using only EO parameters with RMSE of 704-938 kg/ha using a non-linear model, but the results are only slightly poorer if a linear model is used. It compares well to a model that also includes weather data, showing that a model can be driven by optical EO data alone.

Fractional holographic dark energy

Holographic dark energy theories present a fascinating interface to probe late-time cosmology, as guided by contemporary ideas about quantum gravity. In this work, we present a new holographic dark energy scenario designated “Fractional Holographic Dark Energy” (FHDE). This model extends the conventional framework of HDEs by incorporating specific features from fractional calculus and fractional Wheeler-De Witt equation recently applied, e.g., in cosmological settings. In this manner, we retrieve a novel form of HDE energy density. We then show how FHDE can provide a consistent picture of the evolution of the late-time universe even with the simple choice of the Hubble horizon as the IR (infrared) cutoff. We provide detailed descriptions of the cosmological evolution, showing how the fractional calculus ingredients can alleviate quite a few issues associated with the conventional HDE scenario. Concretely, we compute and plot diagrams using the Hubble horizon cutoff for HDE. The density parameters for DE and dark matter (DM), the deceleration parameter, and the DE EoS parameter indicate how the universe may evolve within our “FHDE” model, fitting within an appropriate scenario of late-time cosmology.

Computation of bulk viscous pressure with observational constraints via scalar field in the General relativity and [formula omitted] gravity

The present article deals with the isotropic cosmological model of f(Q) gravity filled with bulk viscous fluid, where Q is the non-metricity term and it is responsible for the gravitational interaction. Aside from the tachyon and quintessence scalar fields, the modified Einstein’s field equations have been resolved through the application of the power law form of the expansion. In this model, the Markov chain Monte Carlo (MCMC) analysis method has been utilized to obtained the best-fit value of the model parameter and it confirms that the model satisfies the recent observational data. We have also examined the EoS parameter for bulk viscosity in these cosmological contexts and it has been determined that ωeff will be located in the phantom region. The correspondence between bulk pressure and the reconstructed ωrec,Q in f(Q) gravity has also been addressed. In the presence of holographic Ricci dark energy, the reconstructed f(Q) gravity yields a transition from the quintessence era into phantom era.

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.

Metric-Affine F(T,Q) gravity: cosmological implications and constraints

Abstract In this paper, we investigate some exact cosmological models in Metric-Affine $F(T,Q)$ gravity, with observational constraints. The Metric-Affine $F(T,Q)$ gravity is some kind of unification of two known gravity theories, namely, the $F(T)$ gravity and the $F(Q)$ gravity. We obtain the field equations of the Metric-Affine theory by considering the metric tensor and the general affine connection as independent variables. We then focus on the particular case in which the $F(T,Q)$ function characterizing the aforementioned metric-affine models is linear, that is, $F(T,Q)=\lambda T+\mu Q$. We investigate this linear case and consider a Friedmann-Lema\^{i}tre-Robertson-Walker background to study cosmological aspects and applications. We have obtained three exact solutions of the modified field equations in two different cases, $T$ and $Q$, using the Hubble function $H(t)$ and the scale factor $a(t)$. We then placed observational constraints on these solutions using the Hubble $H(z)$ datasets and the MCMC analysis. We have investigated the deceleration parameter $q(z)$ and effective EoS parameters, and a comparative study of all three models with $\Lambda$CDM model has been carried out.

Power Law f(Q)$f(Q)$ Cosmology with Bulk Viscous Fluid

AbstractIn this work, a power law model is explored, specifically, , along with viscous matter fluid having transport coefficient . The corresponding analytical solution is derived and then confronted with recent cosmic data. The Markov Chain Monte Carlo (MCMC) sampling technique is utilized to estimate the mean value of arbitrary parameters, by incorporating Cosmic Chronometers and recently published Pantheon+Analysis samples. In addition, some cosmological parameters are reconstructed by resampling the chains obtained by emcee, incorporating 6000 samples. It is found that the matter‐energy density depicts the expected positive behavior, whereas the effective pressure indicates the negative behavior that is leading the accelerating expansion, which is further predicted in the effective EoS parameter. Further, the asymptotic nature of the assumed model is investigated by invoking phase‐space analysis. It is concluded that the assumed viscous model successfully predicts an evolution of the universe from decelerated epoch to stable accelerated de‐Sitter epoch.

Cosmographic analysis of anisotropic Kaniadakis holographic dark energy model

In this paper, we investigate the anisotropic and spatially homogeneous Bianchi type-I universe with Kaniadakis holographic dark energy in Saez–Ballester [Phys. Lett. A 113, 467 (1986)] theory of gravitation. We determine Kaniadakis holographic dark energy model by assuming a correlation between the metric potentials to solve the field equations of the model. This results in a dynamical deceleration parameter which demonstrates an accelerating expansion of the universe. Our model’s equation of state parameter [Formula: see text] close to [Formula: see text] ([Formula: see text] model) at late-times and is in agreement with the most recent observations. Next, we obtained the squared sound speed ([Formula: see text]) and found that it is positive, implying stability against perturbations. The [Formula: see text] plane is constructed to investigate the evolution of the models’ EoS parameter turned out to be in a freezing zone. As should be the case in an expanding universe, the strong energy conditions of the model are violated. Statefinders [Formula: see text], and [Formula: see text] planes were also examined. Our model includes the Chaplygin gas, [Formula: see text] limit, and is inclined towards the steady-state model.

Behaviours of rip cosmological models in f(Q,C) gravity

In this study, the Universe's rip cosmology theories have been provided for the f(Q,C) gravity theory, where Q and C stand for the non-metricity scalar and boundary term. We assume f(Q,C)=αQn+βC and analyze the nature of the physical parameters for the Little Rip (LR), Big Rip (BR) and Pseudo Rip (PR) models. In the LR and PR models, the EoS parameter exhibits phantom characteristics but remains closely aligned with the ΛCDM line. The non-metricity term Q has direct effect on the rip models. After investigating the energy conditions, we recognise that our model violates the strong energy constraint. Avoiding singularity situations has been noted in all of these accelerated models. The characteristics of the jerk and snap parameters have been investigated. Our model provides an effective description of the Universe's evolutionary history and fits well with contemporary cosmic data.

Quintessence scalar field model in Weyl-type f(Q, T) gravity with wD – w′D analysis

In the present study, we explore the dynamical characteristics of the quintessence cosmological model in Weyl-type f( Q, T) gravity. Here, T represents the trace of the matter energy–momentum tensor, and Q symbolizes the non-metricity tensor. We propose a solution to the field equation using the specific parametrization in the form q = β z(1 + z)−1 + α, which depicts the necessary transition of cosmos from decelerating era to the current accelerating scenario. The values of model parameters are estimated as H0 = 69.8 ± 1.2, α = −0.64 ± 0.027, and β = 1.549 ± 0.079 using the Markov Chain Monte Carlo analysis and limiting the model with a joint dataset of Pantheon, baryon acoustic oscillation, and cosmic chronometer. We discuss the cosmic behavior of many features of the derived model like EoS parameters, energy density, and cosmic pressure. Further, we have also explored the cosmological behavior of the quintessence model in Weyl f( Q, T) gravity. We have described the cosmic behavior of the model by [Formula: see text] analysis. The diagnosis of the model is also performed using statefinders and jerk parameters. In the end, we have discussed the energy conditions for the proposed model.

Model-independent parameterization of H(z) and its implications for cosmic evolution

We investigate the model-independent parameterization of H(z) in spatially homogeneous and isotropic FLRW space-time using Cosmic Chronometers (31 data points) and Pantheon+SH0ES (1701 points) datasets. The best-fit values for the model parameters (H0,A1,A2,A3) are obtained through MCMC analysis. Our results show that the EoS parameter ω transitions from a matter-dominated era through quintessence to ω=−1, indicating convergence to ΛCDM at late times. The current ω values suggest an accelerating universe. Moreover, the model's squared sound speed vs2 evolves from negative to positive, indicating increasing stability. The deceleration parameter q shows a smooth transition from deceleration to acceleration, with transition redshift zt between 0.5 and 0.8. Further, the energy conditions are satisfied, and SEC violation at z=0 supports current acceleration. The ω−ω′ plane lies in the freezing region, and the r−s plane approaches the ΛCDM limit at late times.

FRW Universe with a Parameterization of the EoS Parameter in f(Q) Gravity

FRW Universe with a Parameterization of the EoS Parameter in f(Q) Gravity

Signature flips in time-varying Λ(t)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda (t)$$\\end{document} cosmological models with observational data

In this study, we investigate signature flips within the framework of cosmological models featuring a time-varying vacuum energy term Λ(t)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda (t)$$\\end{document}. Specifically, we consider the power-law form of Λ=αHn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda =\\alpha H^n$$\\end{document}, where α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document} and n are constants. To constrain the model parameters, we use the MCMC technique, allowing for effective exploration of the model’s parameters. We apply this approach to analyze 31 points of observational Hubble Data (OHD), 1048 points from the Pantheon data, and additional CMB data. We consider three scenarios: when n is a free parameter (Case I), when n=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n=0$$\\end{document} (Case II), and when n=1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n=1$$\\end{document} (Case III). In our analysis across all three cases, we observe that our model portrays the universe’s evolution from a matter-dominated decelerated epoch to an accelerated epoch, as indicated by the corresponding deceleration parameter. In addition, we investigate the physical behavior of total energy density, total EoS parameter, and jerk parameter. Our findings consistently indicate that all cosmological parameters predict an accelerated expansion phase of the universe for all three cases (q0<0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q_0<0$$\\end{document}, ω0<-13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega _0<-\\frac{1}{3}$$\\end{document}, j0>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$j_0>0$$\\end{document}). Furthermore, our analysis reveals that the Om(z) diagnostics for Cases I and III align with the quintessence region, while Case II corresponds to 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.

Thermodynamic properties and revised Helgeson-Kirkham-Flowers equations of state parameters of the hydrated and dehydrated monomeric silica species at t = 0.01–600oC, P = 1–3000 bars, ρH2O = 0.35–1.1 g cm−3, and Im= 0 m

The thermodynamic properties and revised Helgeson-Kirkham-Flowers equations of state (r-H-K-F EoS) parameters of the hydrated (Si(OH)4(aq), SiO(OH)3– and SiO2(OH)22−) and corresponding dehydrated (SiO2(aq), HSiO3− and SiO32−) monomeric silica species are important to describe the pH, composition, temperature, and pressure dependence of formation/breakdown reactions of all silicon-bearing compounds globally. Experimental log10 equilbrium constant, K values describing the formation reactions of these hydrated and dehydrated monomeric silica species were therefore compiled from the literature, extrapolated to zero ionic strength by specific ion interaction theory as required and used to derive their thermodynamic properties and r-H-K-F EoS parameters.Consideration of all formation reactions in the same study provides a collective, internally consistent update to the thermodynamic properties and r-H-K-F EoS parameters of the monomeric silica species that are able to provide satisfactory matches to the available experimental log10 K values at t = 0.01–600oC, P = 1–3000 bars, ρH2O = 0.35–1.1 g cm−3, and zero ionic strength. These temperature and pressure limits comfortably bracket t = 0.01–100oC and P = 1–270 bars relevant to the geological disposal of radioactive wastes at depths of up to 1 km.Updates to the thermodynamic properties of silicon-bearing compounds in all of the available geochemical thermodynamic databases are necessary, especially if reaction properties are used or given. Internal consistency between the hydrated and dehydrated species means that the hydrated species alone can be used as entries in geochemical thermodynamic databases.

Late time acceleration in Bianchi type-V dark energy cosmological models with linear deceleration parameter

We present a Bianchi type-V cosmological model with deceleration parameter as a simple linear function of the Hubble parameter interacting with a perfect fluid in the general theory of relativity. For Bianchi type-V space-time, the available solutions of Einstein field equations have been procure under the assumption of linear deceleration parameter, q = A + BH, where H is the Hubble parameter. Also,during the evolution of the Bianchi-V universe, dark energy(DE) with a variable EoS parameters has been studied in detail and w slowly varies around w = –0.33 for a 10 GYr. lapse, which involves an accelerated expansion, through an expansion not compatible with current. In this article, we discuss the physical and geometrical facets of the cosmological parameter of the model. Several elements of the model universe are explained by the jerk parameter and energy conditions, including the recent cosmological expansion and singularity theories. We also deliberated state-finder parameters, which forecast that the Universe created from Einstein’s static era rallies towards ΛCDM model (r = 1, s = 0).

Cosmology in non-coincident gauge formulation of f(Q,C) gravity theory

This paper is an investigation of dark energy cosmological models in non-coincident gauge formulation of non-metricity gravity with boundary term. We have considered an arbitrary function [Formula: see text], where [Formula: see text] is the non-metricity scalar, [Formula: see text] is the boundary term derived by [Formula: see text], and [Formula: see text] are the model parameters, to obtain the modified field equations from action. We have parameterized the Hubble function as [Formula: see text] with [Formula: see text] are arbitrary constants and [Formula: see text] is the scale-factor depending upon cosmic time. We have compared this Hubble function with [Formula: see text] datasets and obtained best fit values of model parameters using likelihood analysis. Using these best fit values of model parameters, we have done our result analysis and discussion with cosmological parameters viz effective equation of state parameter, energy density, energy conditions, deceleration parameter, om diagnostic analysis and age of the universe. We have found a transit phase universe model with effective EoS parameter [Formula: see text] over redshift [Formula: see text].

Linear redshift parametrization of deceleration parameter in [formula omitted] gravity

In this study, we investigate the linear redshift parametrization of q(z) within the framework of f(R,Lm) gravity, using constraints derived from H(z)/Pantheon samples. We consider a non-linear functional form for f(R,Lm), specifically given by f(R,Lm)=R2+Lmn, where n represents a free parameter in the model. Subsequently, we derive the solution for the Hubble parameter by investigating the parametrization of q(z) and then apply this solution to the modified Friedmann equations. Our analysis focuses on exploring the behavior of the EoS parameter across different stages of the universe’s evolution, including radiation, matter, and dark energy eras. Furthermore, our results confirm the quintessence nature of the universe’s current accelerated expansion phase (−1<ω<−13), supporting the role of quintessence in driving the universe’s current acceleration. We also explore the redshift dependence of the deceleration parameter, statefinder, Om(z) diagnostics, energy density, pressure, and energy conditions to determine the universe’s accelerating behavior. Importantly, our findings suggest that the linear redshift parametrization of q(z), supported by additional terms in f(R,Lm) gravity, provides a compelling alternative to the cosmological constant.

Dynamical system analysis of Dirac-Born-Infeld scalar field cosmology in coincident f(Q) gravity* *SG acknowledges the Council of Scientific and Industrial Research (CSIR), Government of India, New Delhi, for a junior research fellowship ( 09/1026(13105)/2022-EMR-I). RS acknowledges the University Grants Commission (UGC), New Delhi, India, for awarding a Senior Research Fellowship (UGC-Ref. No.: 191620096030). PKS acknowledges the Science and Engineering Research

In this article, we present a dynamical system analysis of a Dirac-Born-Infeld scalar field in a modified gravity context. We considered a polynomial form of modified gravity, used two different types of scalar potential, polynomial and exponential, and found a closed autonomous dynamical system of equations. We analyzed the fixed points of such a system and evaluated the conditions under which deceleration to late-time acceleration occurs in this model. We note the similarity of the two models and show that our result is consistent with a previous study on Einstein's gravity. We also investigated the phenomenological implications of our models by plotting EoS (ω), energy density (Ω), and deceleration parameter (q) w.r.t. to e-fold time and comparing to the present value. We conclude the paper by observing how the dynamical system analysis differs in the modified gravity, and present the future scope of our research.

Probing the universe's expansion dynamics: The linear correction scenario perspective on dark energy

In this study, we investigate the cosmological evolution of the universe, focusing on the KMMS models in a model-independent approach, particularly the scenario involving linear correction, given by E2(z)=A(z)+β(1+γB(z)), where A(z)=Ωm0(1+z)3 and B(z)=z. By analyzing recent Cosmic Chronometers (CC) and the Pantheon+ samples, we determine the best-fit values of model parameters using a Markov chain Monte Carlo analysis. Our models exhibit unique dynamics, transitioning from super-exponential to exponential expansion, with a significant shift at redshift zt=0.83−0.10+0.11 and present deceleration parameter q0=−0.69−0.17+0.17. The jerk parameter exceeds 1, indicating a faster change in acceleration than predicted by ΛCDM. The energy density parameter is consistent with Planck observations, and the dark sector evolution follows the expected thermal history. The EoS parameter approaches ωde=−1 over time, with a current value of ωde0=−1.06±0.12, aligning with the phantom phase. Our model presents a new dark energy alternative, emphasizing the importance of considering models like KMMS in understanding cosmic evolution.