arXiv subjects

Anirudh Pradhan

Publications and source records attributed to Anirudh Pradhan.

At least 109 records · Page 6Linked to original sources

arXiv2021

A new topological perspective of expanding space-times with applications to cosmology

We discuss the possible role of the Tietze extension theorem in providing a rigorous topological base to the expanding space-time in cosmology. A simple toy model has been introduced to show the analogy between the topological extension from a circle $S$ to the whole space $M$ and the cosmic expansion from a non-zero volume to the whole space-time in non-singular cosmological models. A topological analogy to the cosmic scale factor function has been suggested, the paper refers to the possible applications of the topological extension in mathematical physics.

physics.gen-ph↗

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

Role of a periodic varying deceleration parameter in Particle creation with higher dimensional FLRW Universe

The present search focus on the mechanism of gravitationally influenced particle creation (PC) in higher dimensional Friedmann-Lemaitre-Robertson-Walker(FLRW) cosmological models with a cosmological constant (CC). The solution of the corresponding field equations is obtained by assuming a periodically varying deceleration parameter (PVDP) i.e. $q= m \cos kt - 1$ [Shen and Zhao, Chin. Phys. Lett., 31 (2014) 010401] which gives a scale factor $a(t) = a_0 \left[\tan \left(\frac{kt}{2}\right)\right]^\frac{1}{m}$, where $a_0$ is the scale factor at the current epoch. Here $k$ displays the PVDP periodicity and can be regarded as a parameter of cosmic frequency, $m$ is an enhancement element that increases the PVDP peak. Here, we investigated the periodic variation behavior of few quantities such as the deceleration parameter $q$, the energy density $ρ$, PC rate $ψ$, the entropy $S$, the CC $Λ$, Newton's gravitational constant $G$ and discuss their physical significance. We have also explored the density parameter, proper distance, angular distance, luminosity distance, apparent magnitude, age of the universe, and the look-back time with redshift $z$ and have observed the role of particle formation in-universe evolution in early and late times. The periodic nature of various physical parameters is also discussed which are supporting the recent observations.

physics.gen-ph↗

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

Color-flavor locked quark stars in energy-momentum squared gravity

Several attempts have been made in the past decades to search for the true ground state of the dense matter at sufficiently large densities and low temperatures via compact astrophysical objects. Focusing on strange stars, we derive the hydrostatic equilibrium assuming a maximally symmetric phase of homogeneous superconducting quark matter called the \textit{color-flavor-locked} (CFL) phase in the background of energy-momentum squared gravity (EMSG). Theoretical and experimental investigations show that strange quark matter (SQM) in a CFL state can be the true ground state of hadronic matter at least for asymptotic densities, and even if the unequal quark masses. Motivated by these theoretical models, we explore the structure of stellar objects in recently proposed EMSG, which allows a correction term $T_{μν}T^{μν}$ in the action functional of the theory. Interestingly, EMSG may be effective to resolve the problems at high energy densities, e.g., relevant to the early universe and dense compact astrophysical objects without invoking some new forms of fluid stress, such as bulk viscosity or scalar fields. Finally, we solve the complicated field equations numerically to obtain the mass-radius relations for strange stars in CFL equation of state.

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

A flat FRW model with dynamical $Λ$ as function of matter and geometry

We revisit the evolution of the scale factor in a flat FRW spacetime with a new generalized decay rule for the dynamic $Λ$-term under modified theories of gravity. It analyses certain cosmological parameters and examines their behaviours in this generalized setting which includes several decay laws in the literature. We have also obtained observational constraints on various model parameters and estimated the present values of cosmological parameters $\{Ω_{m_0}$, $Ω_{Λ_0}$, $q_{0}, t_{0}$, $ω_{0}\}$ and have discussed with various observational results. Finite time past and future singularities in this model are also discussed. \end{abstract}

physics.gen-ph↗

arXiv2020

Anisotropic Compact stars in the Buchdahl model: A comprehensive study

In this article, we present a class of relativistic solutions describing spherically symmetric and static anisotropic stars in hydrostatic equilibrium. For this purpose, we consider a particularized matric potential, namely, Buchdahl ansatz [Phys. Rev. D \textbf{116}, 1027 (1959).] which encompasses almost all the known analytic solutions to the spherically symmetric, static Einstein field equations(EFEs) with a perfect fluid source, including in particular the Vaidya-Tikekar and Finch-Skea. We here developed the model by considering an anisotropic spherically symmetric static general relativistic configuration that plays a significant effect on the structure and properties of stellar objects. We have considered eight different cases for generalized Buchdahl dimensionless parameter $K$, and analyzed them in a uniform manner. As a result, it turns out that all the considered cases are valid at every point in the interior spacetime. In addition to this, we show that the model satisfies all the energy conditions and maintains the hydrostatic equilibrium equation. In the framework of the anisotropic hypothesis, we consider analogue objects with similar mass and radii such as LMC X-4, SMC X-1, EXO 1785-248 \emph{etc} to restrict the model parameter arbitrariness. Also, establishing a relation between pressure and density in the form of $P = P (ρ)$, we demonstrate that EoSs can be approximated to a linear function of density. Despite the simplicity of this model, the obtained results are satisfactory.

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↗

arXiv2020

Probing $κ(R,T)$ cosmology via empirical approach

In this paper, a stable flat cosmological model has been constructed and the evolution of dark energy has been investigated in the framework of the recently suggested $κ(R,T)$ gravity. The empirical approach we adopt in the current work reveals some interesting cosmological features consistent with observations and the standard $Λ$CDM model. The evolution of cosmic pressure shows a positive-to-negative transition corresponding to the cosmic deceleration-acceleration transition, both the deceleration parameter and the cosmic pressure have the positive-to-negative sign flipping. While this behavior can provide explanation for the deceleration-acceleration transition, the reason behind this positive-negative transition itself is still missing.

gr-qc↗

arXiv2019

Crossing the phantom divide line in universal extra dimensions

We investigate the cosmic acceleration and the evolution of dark energy across the cosmological constant boundary in universal extra dimensions UED. We adopt an empirical approach to solve the higher-dimensional cosmological equations so that the deceleration parameter $q$ is consistent with observations. The expressions for the jerk and deceleration parameters are independent of the number of dimensions $n$. The behavior of pressure in $4$D shows a positive-to-negative transition corresponding to the deceleration-to-acceleration cosmic transition. This pressure behavior helps in providing an explanation to the cosmic deceleration-acceleration transition although the reason behind the transition itself remains unknown. In the conventional $4$D cosmology, there is a no-go theorem prevents the EoS parameter of a single perfect fluid in FRW geometry to cross the $ω=-1$ boundary. The current model includes a single homogenous but anisotropic perfect fluid in a homogenous FRW metric with two different scale factors in the ordinary $4$D and the UED. In contrast to the conventional $4$D cosmology, we have found that the dark energy evolution in UED shows $ω=-1$ crossing. however, the no-go theorem is still respected in $4$D where the EoS parameter doesn't cross the $ω=-1$ boundary.

gr-qc↗