arXiv subjects

Archana Dixit

Publications and source records attributed to Archana Dixit.

At least 37 records · Page 2Linked to original sources

arXiv2023

Transit String Dark Energy Models in $f(Q)$ Gravity

In this paper, we have investigated an anisotropic cosmological model in $f(Q)$ gravity with string fluid in LRS Bianchi type-I universe. We have considered the arbitrary function $f(Q)=Q+α\sqrt{~Q}+2Λ$ where $α$ is model free parameter and $Λ$ is the cosmological constant. We have established a relationship between matter energy density parameter $Ω_{m}$ and dark energy density parameter $Ω_Λ$ through Hubble function using using constant equation of state parameter $ω$. We have made observational constraint on the model using $χ^2$-test with observed Hubble datasets $H(z)$ and SNe Ia datasets, and obtained the best fit values of cosmological parameters. We have used these best fit values in the result and discussion. We have discussed our result with cosmographic coefficients and found a transit phase dark energy model. Also, we analyzed the Om diagnostic function for anisotropic universe and found that our model is quintessence dark energy model.

gr-qc↗

arXiv2022

Observational constraints for an axially symmetric transitioning model with bulk viscosity parameterization

In this paper, we have analyzed the significance of bulk viscosity in an axially symmetric Bianchi type-I model to study the accelerated expansion of the universe. We have considered four bulk viscosity parameterizations for the matter-dominated cosmological model. The function of the two significant Hubble $H(z)$ and deceleration parameters are discussed in detail. The energy parameters of the universe are computed using the most recent observational Hubble data (57 data points) in the redshift range $0.07 \leq z \leq 2.36)$. In this model, we obtained all feasible solutions with the viscous component and analyzed the universe's expansion history. Finally, we analyzed the statefinder diagnostic and found some interesting results. The outcomes of our developed model now properly align with observational results.

gr-qc↗

arXiv2022

Quintessence Behaviour of an Anisotropic Bulk Viscous Cosmological Model in Modified $f(Q)$-Gravity

In this article, we have discussed the results of our investigation. We consider an anisotropic viscous cosmological model of (LRS) Bianchi type I spacetime universe filled with a viscous fluid under $f(Q)$ gravity. We have studied the modified $f(Q)$ gravity with quadratic form $f(Q)=αQ^{2}+β$, where $Q$ is called as a non-metricity scalar and $α$, $β$ are positive constants. We obtain the modified Einstein field equation by considering the viscosity coefficient $ξ(t)=ξ_{0}H$ and obtained the scale factor $a(t)=2~sinh\left (\frac{m+ 2} {6}\sqrt{\frac{ξ_{0}}{α(2m+1)}}t\right)$.We applied the observational constraint on the apparent magnitude $m(z)$ using the $χ^{2}$ test formula with observational data set like JLA or Union 2.1 compilation and obtained the best approximate values of the model parameters ${ m,α, H_{0} ξ_{0}}$. We have analyzed our model and found a transit phase quintessence anisotropic accelerating universe. We also examined the bulk viscosity equation of state (EoS) parameter $ω_{v}$ and obtained its current value as $ω_{v}<-1/3$, which shows the dark energy dominant model, cosmological constant, phantom, and super-phantom dark energy models, and tends to the $Λ$CDM value ($ω_{v}=-1$) in the late time. We also estimate the current age of the universe as $t_{0}\approx13.6$ Grys and analyze the Statefinder parameters with $(s,r)\to(0,1)$ as $t \to \infty$.

gr-qc↗

arXiv2022

Renyi Holographic Dark Energy models in Teleparallel gravity

In this paper, we have investigated the physical behavior of cosmological models in the framework of modified Teleparallel gravity. This model is established using a Renyi holographic ``dark energy model (RHDE) with a Hubble cutoff. Here we have considered a homogeneous and isotropic Friedman universe filled with perfect `fluid. The physical parameters are derived for the present model in Compliances with 43 observational Hubble data sets (OHD). The equation of state (EoS) parameter in terms of $H(z)$ describes a the transition of the universe between phantom and non-phantom phases in the context of $f(T)$ gravity. Our model shows the violation of strong energy condition (SEC) and the weak energy condition (WEC) over the accelerated phantom regime. We also observed that these models occupy freezing regions through $ω_{D} -ω_{D}^{'}$ plane. Consequently, our Renyi HDE model is supported to the consequences of general relativity in the framework of $f(T)$ modified gravity.

gr-qc↗

arXiv2022

Bianchi type-V Transitioning model in Brans-Dicke theory with Observational Constraint

In this paper, we have examined the viability of the Bianchi type-V universe in Brans-Dicke (BD) theory of gravitation. We have discussed the interacting and non-interacting scenarios between dark matter (DM) and dark energy (DE) of the derived universe within the framework of BD theory. CCA technique has been applied to constrain the model parameters using 46 values of observational Hubble data (OHD), Pantheon data (the latest compilation of SNIa with 40 binned in the redshift range $0.014 \leq z \leq 1.62)$ and their combined datasets. We establish an exact solution of the field equations to derive the dynamics of the derived universe and the obtained results are found to agree with the observations. We also noted a distinctive change in the sign of the deceleration parameter from positive to negative, as well as the presence of a transition red-shift exists. Using various observational data points, the evolution trajectories for $(r~- s)$ diagnostic planes are shown to understand the geometrical behavior of the Bianchi-V model. Some physical properties of the universe are also discussed. It's also worth noting that the conclusions of the cosmological parameter are consistent with modern observational data.

gr-qc↗

arXiv2022

An Axially Symmetric Transitioning models with Observational Constraints

In this study, we have demonstrated the expansion history of an axially symmetric Bianchi type-I model of the universe. Our model as of now presents an accelerating universe, which had been in the decelerating phase in the past. Roles of the two crucial Hubble~$H(z)$ and deceleration~$q(z)$ parameters are examined. The energy parameters of the universe are estimated with the help of the latest observational Hubble data (46-data points) and Pantheon data (the latest compilation of SNIa with 40 binned in the redshift range $0.014 \leq z \leq 1.62)$. We also discuss the stability analysis of the model by state finder diagnosis. The analysis reveals that in late time, the model is a quintessence type and points towards the $Λ$CDM model. Our developed model agrees with observational findings in a proper way. We have discussed some of the physical aspects of the model.

gr-qc↗

arXiv2022

A new class of holographic dark energy models in LRS Bianchi Type-I

In this paper, we examine the (LRS) Bianchi-type-I cosmological model with holographic dark energy. The exact solutions to the corresponding field equations are obtained by using generalized hybrid expansion law (HEL). The EoS parameter $ω$ for DE is found to be time dependent and redshift dependent and its exiting range for derived model is agreeing well with the current observations. Here we likewise apply two mathematical diagnostics, the statefinder ({r, s}) and $ω_{d}-ω^{'}_{d}$ plane to segregate HDE model from the $ΛCDM$ model. Here the $ω_{d}-ω^{'}_{d}$ diagnostic trajectories is the good tool to classifying the dynamical DE model. We found that our model lies in both thawing region and freezing region. We have also construct the potential as well as dynamics of the quintessence and tachyon scalar field. Some physical and geometric properties of this model along with the physical acceptability of cosmological solution have been discussed in detail.

gr-qc↗

arXiv2021

Barrow HDE model for Statefinder diagnostic in non-flat FRW universe

In this work we study a non-flat Friedmann-Robertson-Walker universe filled with a pressure-less dark matter (DM) and Barrow holographic dark energy (BHDE) whose IR cutoff is the apparent horizon. Among various DE models, (BHDE) model shows the dynamical enthusiasm to discuss the universe's transition phase. According to the new research, the universe transitioned smoothly from a decelerated to an accelerated period of expansion in the recent past. We exhibit that the development of $q$ relies upon the type of spatial curvature. Here we study the equation of state (EoS) parameter for the BHDE model to determine the cosmological evolution for the non-flat universe. The (EoS) parameter and the deceleration parameter (DP) shows a satisfactory behaviour, it does not cross the the phantom line. We also plot the statefinder diagram to characterize the properties of the BHDE model by taking distinct values of barrow exponent $\triangle$. Moreover, we likewise noticed the BHDE model in the $(ω_{D}-ω_{D}^{'})$ plane, which can furnish us with a valuable, powerful finding to the mathematical determination of the statefinder. In the statefinder trajectory, this model was found to be able to reach the $ΛCDM$ fixed point.

gr-qc↗

arXiv2021

Statefinder hierarchy model for the Barrow holographic dark energy

In this paper, we have used the state finder hierarchy for Barrow holographic dark energy (BHDE) model in the system of the FLRW Universe. We apply two DE diagnostic tools to determine $ΛBHDE$ model to have various estimations of $\triangle$. The first diagnostic tool is the state finder hierarchy in which we have studied $S^{(1)}_{3}$ $S^{(1)}_{4}$, $S^{(2)}_{3}$ $S^{(2)}_{4}$ and second is the composite null diagnostic (CND) in which the trajectories ( $S^{(1)}_{3} - ε$), ($S^{(1)}_{4}-ε$), ($S^{(2)}_{3}-ε$)($S^{(2)}_{4}-ε$) are discussed, where $ε$ is fractional growth parameter. The infrared cut-off here is taken from the Hubble horizon. Finally, together with the growth rate of matter perturbation, we plot the state finder hierarchy that determines a composite null diagnosis that can differentiate emerging dark energy from $ΛCDM$. In addition, the combination of the hierarchy of the state finder and the fractional growth parameter has been shown to be a useful tool for diagnosing BHDE, particularly for breaking the degeneracy with different parameter values of the model.

gr-qc↗

arXiv2021

Barrow HDE model for Statefinder diagnostic in FLRW Universe

We have analyzed the Barrow holographic dark energy (BHDE) in the framework of the flat FLRW Universe by considering the various estimations of Barrow exponent $\triangle$. Here we define BHDE, by applying the usual holographic principle at a cosmological system, for utilizing the Barrow entropy rather than the standard Bekenstein-Hawking. To understand the recent accelerated expansion of the universe, considering the Hubble horizon as the IR cut-off. The cosmological parameters, especially the density parameter ($Ω_{_D}$), the equation of the state parameter ($ω_{_D}$), energy density ($ρ_{_{D}}$) and the deceleration parameter($q$) are studied in this manuscript and found the satisfactory behaviors. Moreover, we additionally focus on the two geometric diagnostics, the statefinder $(r,s)$ and $O_{m}(z)$ to discriminant BHDE model from the $ΛCDM$ model. Here we determined and plotted the trajectories of evolution for statefinder $(r, s)$, $(r,q)$ and $O_{m}(z)$ diagnostic plane to understand the geometrical behavior of the BHDE model by utilizing Planck 2018 observational information. Finally, we have explored the new Barrow exponent $\triangle$, which strongly affects the dark energy equation of state that can lead it to lie in the quintessence regime, phantom regime, and exhibits the phantom-divide line during the cosmological evolution.

gr-qc↗

arXiv2020

Compatibility between the scalar field models of tachyon, $k$-essence and quintessence in $f(R, T)$ gravity

We investigate the behavior of the scalar field in $f (R, T )$ gravity (Harko et al., Phys. Rev. D 84, 024020, 2011) inside the structure of a flat FRW cosmological model, where $R$ and $T$ have their usual meaning. The deterministic solution of FEs has been settled by considering the scale factor $S(t) = t^{m}e^{kt}$, where $m$ and $k$ are positive constant. Here we utilize three ongoing imperatives ($H_{0}=73.8$ and $ q_{0}=-0.73$) from SNe Ia Union observation (Cunha, Phys. Rev. D 79, 047301, 2009); ($H_{0}=73.8$ and $ q_{0}=-0.55$) from Type Ia Supernova (SNIa) observation in joined with (BAO) and (CMB) observation (Giostri et al., J. Cosmol. Astropart. Phys. 03, 027, 2012); and ($H_{0}=69.2$ and $q_{0}=-0.52)$ from (OHD+JLA) observation (Yu et al., Astrophys. J. 856, 3, 2018). We have measured and graphed several cosmological parameters and found that these findings are appropriate in comparison with the universe's physical and kinematic properties and also compatible with ongoing observations. The correspondence between the scalar field models of tachyon, k-essence, and quintessence is investigated by us. Our model explains the potentials and the dynamics of the scalar fields in the FRW universe. The reconstructed potential is very sensible and has a scaling arrangement. Subsequently, our study supports recent observations.

gr-qc↗

arXiv2020

Stability, dark energy parameterization and swampland aspect of Bianchi Type-$ VI_{h}$ cosmological models with f(R, T)-gravity

Stability, dark energy (DE) parameterization and swampland aspects for the Bianchi form-$VI_{h}$ universe have been formulated in an extended gravity hypothesis. Here we have assumed a minimally coupled geometry field with a rescaled function of $f(R, T)$ replaced in the geometric action by the Ricci scalar $R$. Exact solutions are sought under certain basic conditions for the related field equations. For the following theoretically valid premises, the field equations in this scalar-tensor theory have been solved. It is observed under appropriate conditions that our model shows a decelerating to accelerating phase transition property. Results are observed to be coherent with recent observations. Here, our models predict that the universe's rate of expansion will increase with the passage of time. The physical and geometric aspects of the models are discussed in detail. In this model, we also analyze the parameterizations of dark energy by fitting the EoS parameter $ω(z)$ with redshift. The results obtained would be useful in clarifying the relationship between dark energy parameters. In this, we also explore the correspondence of swampland dark energy. The swampland criteria have also been shown the nature of the scalar field and the potential of the scalar field.

physics.gen-ph↗

arXiv2020

Transit cosmological models with observational constraints in f(Q, T) gravity

This cosmological model is a study of modified $f(Q,T)$ theory of gravity which was recently proposed by Xu {\it et al.} (Eur. Phys. J. C {\bf 79}, 708 (2019)). In this theory of gravity, the action contains an arbitrary function $f(Q,T)$ where $Q$ is non-metricity and $T$ is the trace of energy-momentum tensor for matter fluid. In our research, we have taken the function $f(Q,T)$ quadratic in $Q$ and linear in $T$ as $f(Q,T)=αQ+βQ^{2}+γT$ where $α$, $β$ and $γ$ are model parameters, motivated by $f(R,T)$ gravity. We have obtained the various cosmological parameters in Friedmann-Lemaitre-Robertson-walker (FLRW) Universe viz. Hubble parameter $H$, deceleration parameter $q$ etc. in terms of scale-factor as well as in terms of redshift $z$ by constraining energy-conservation law. For observational constraints on the model, we have obtained the best-fit values of model parameters using the available data sets like Hubble data sets $H(z)$, Joint Light Curve Analysis (JLA) data sets and union $2.1$ compilation of SNe Ia data sets by applying $R^{2}$-test formula. We have calculated the present values of various observational parameters viz. $H_{0}$, $q_{0}$, $t_{0}$ and statefinder parameters $(s,r)$, these values are very close to the standard cosmological models. Also, we have observed that the deceleration parameter $q(z)$ shows signature-flipping (transition) point within the range $0.423\leq z_{t}\leq0.668$ through which it changes its phase from decelerated to accelerated expanding universe with equation of state (EoS) $-1.071\leqω-0.96$ for $0\leq z\leq3$.

physics.gen-ph↗

arXiv2020

RHDE models in FRW Universe with two IR cut-offs with redshift parametrization

In this manuscript, we have researched the cosmic expansion phenomenon in flat FRW Universe through the interaction of the recently proposed R$\grave{e}$nyi holographic dark energy (RHDE). For this reason, we assumed Hubble (H) and Granda--Oliveros (GO) horizons as IR cut-off in the framework of $f(R, T)$ gravity. With this choice for IR cut-off, we can obtain some important cosmological quantities such as the equation of state $ω_{_T}$, energy density $ρ_{_T}$, density parameter $Ω_{_T}$, and pressure $p_{_T}$, which are the function of the redshift $z$. It is observed that in both IR cut-offs the EoS parameter displays quintom-like behaviour for three different values of $δ$. Here we plot these parameters versus redshift $z$ and discuss the consistency of the recent findings. Next, we explore the $ω_{_T}$-$ω_{_T}^{'}$ plane and the stability analysis of the dark energy model by a perturbation method. Our findings demonstrate that the Universe is an accelerating model of rapid growth that is explained by quintom like behaviour.Hence the feasibility of the RHDE model with Hubble and GO cut-off is supported by our model. The results indicate that the IR cut-offs play a significant role in the understanding of the dynamics of the universe.

gr-qc↗

arXiv2020

Transit cosmological models coupled with zero-mass scalar-field with high redshift in higher derivative theory

The present study deals with a flat FRW cosmological model filled with perfect fluid coupled with the zero-mass scalar field in the higher derivative theory of gravity. We have obtained two types of universe models, the first one is the accelerating universe (power-law cosmology) and the second one is the transit phase model (hyperbolic expansion-law). We have obtained various physical and kinematic parameters and discussed them with observationally constrained values of $H_{0}$. The transit redshift value is obtained $z_{t}=0.414$ where the transit model shows signature-flipping and is consistent with recent observations. In our models, the present values of EoS parameter $ω_{0}$ crosses the cosmological constant value $ω_{0}=-1$. Also, the present age of the universe is calculated.

physics.gen-ph↗

arXiv2020

Traversable wormholes with logarithmic shape function in f(R, T) gravity

In the present work, a new form of the logarithmic shape function is proposed for the linear $f(R,T)$ gravity, $f(R,T)=R+2λT$ where $λ$ is an arbitrary coupling constant, in wormhole geometry. The desired logarithmic shape function accomplishes all necessary conditions for traversable and asymptotically flat wormholes. The obtained wormhole solutions are analyzed from the energy conditions for different values of $λ$. It has been observed that our proposed shape function for the linear form of $f(R,T)$ gravity, represents the existence of exotic matter and non-exotic matter. Moreover, for $λ=0$ i.e. for the general relativity case, the existence of exotic matter for the wormhole geometry has been confirmed. Further, the behaviour of the radial state parameter $ω_{r}$, the tangential state parameter $ω_{t}$ and the anisotropy parameter $\triangle$ describing the geometry of the universe, has been presented for different values of $λ$ chosen in $[-100,100]$.

physics.gen-ph↗

arXiv2020

Cosmological models of generalized ghost pilgrim dark energy (GGPDE) in the gravitation theory of Saez-Ballester

We are studying the mechanism of the cosmic model in the presence of GGPDE and matter in LRS Bianchi type-I space-time by the utilization of new holographic DE in Saez-Ballester theory. Here we discuss all the data for three scenarios, first is supernovae type Ia union data, second is SN Ia data in combination with BAO and CMB observations and third is combination with OHD and JLA observations. From this, we get a model of our universe, where its transit state from deceleration to acceleration phase. Here we have observed that the results yielded by cosmological parameters like $ρ$ (energy density), EoS (equation of state), squared speed of sound $(v_s^2)$, $(ω_D-ω_D^{'})$ and $(r-s)$ plane is compatible with the recent observational data. The $(ω_D-ω_D^{'})$ trajectories in both thawing and freezing regions and the correspondence of the quintessence field with GGPD dark energy are discussed. Some physical aspects of the GGPDE models are also highlighted.

physics.gen-ph↗

arXiv2020

An FLRW interacting dark energy model of the Universe

In this paper, we have presented an FLRW universe containing two-fluids (baryonic and dark energy) with a deceleration parameter (DP) having a transition from past decelerating to the present accelerating universe. In this model, dark energy (DE) interacts with dust to produce a new law for the density. As per our model, our universe is at present in a phantom phase after passing through a quintessence phase in the past. The physical importance of the two-fluid scenario is described in various aspects. The model is shown to satisfy current observational constraints such as recent Planck results. Various cosmological parameters relating to the history of the universe have been investigated.

physics.gen-ph↗