arXiv subjects

Anirudh Pradhan

Publications and source records attributed to Anirudh Pradhan.

At least 55 records · Page 3Linked to original sources

arXiv2025

The effect of pressure anisotropy on quark stars structure in the Starobinsky model

The structure and stability of quark stars (QSs) made of interacting quark matter are discussed in this study, taking color superconductivity and perturbative QCD corrections into account. By combining this EoS with the Tolman-Oppenheimer-Volkoff (TOV) equations, we explore the mass-radius ($M-R$) relations of QSs. The analysis is conducted within the framework of $R^2$ gravity, where the gravity model is described by $f(R) = R + a R^2$. Our primary goal is to investigate how variations in the $R^2$ gravity parameter $a$ affect the mass-radius and mass-central density ($M-ρ_c$) relationships of QSs. Furthermore, we study the dynamical stability of these stars by analyzing the impact of anisotropy parameters $β$ and the interaction parameter $λ$ derived from the EoS, on their stability. Our results demonstrate that the presence of pressure anisotropy plays a significant role in increasing the maximum mass of QSs, with potential implications for the existence of super-massive pulsars. These findings are in agreement with recent astronomical observations, which suggest the possibility of neutron stars exceeding $2M_{\odot}$.

hep-th↗

arXiv2025

Observational constraints in late time for an axially symmetric transitioning model with bulk viscous fluid

In this paper, we explore an axially symmetric Bianchi type-I model of the universe with bulk viscous fluid as a source of gravitational field under the framework of Einstein's field equations by assuming barotropic bulk viscous pressure as $-3ζH^2$. The model parameters have been estimated with the help of four data sets: The Hubble 46 data set describes Hubble parameter values at various redshifts, Union 2.1 compilation data sets comprise a distance modulus of 580 SNIa supernovae at different redshifts, the Pantheon data set contains Apparent magnitudes of 1048 SNIa supernovae at various redshifts and finally BAO data set of volume averaged distances at 5 redshifts. The observational data is analyzed using the traditional Bayesian methodology, and the posterior distributions of the parameters are obtained using the Markov Chain Monte Carlo (MCMC) technique. To get the best-fit values for the model parameters for MCMC analysis, we use the $ emcee $ package. For parameter estimation, we have also employed the minimizing $χ^{2}$ function. We also tried to achieve these values statistically using combined data sets from the four described earlier. The OHD+BAO~and~OHD+Pan+BAO+Union combined data sets provide the best fit Hubble parameter value $H_0$ as $66.912 ^{+0.497}_{-0.501})$ Km/s/Mpc and $74.216 ^{+0.150}_{-0.148}$ Km/s/Mpc respectively. We have performed state finder diagnostics to discuss the nature of dark energy. Some other geometrical parameters like the Jerk parameter and the Om diagnostic are also being discussed to clarify the nature of the dark energy model. The study reveals that the model behaves like a quintessence in late time and approaches the $Λ$ CDM model.

gr-qc↗

arXiv2025

An Accelerating Flat FLRW Model with Observation Constraints and Dynamic $Λ$

In this paper, we explore power law solution of FLRW universe model that is associated with a variable cosmological term $Λ(t)$ as a linear function of $\frac{\ddot{a}}{a}, (\frac{\dot{a}}{a})^2$ and $ρ$. The model parameters were estimated on the basis of the four data sets: The Hubble 46 data, the Union 2.1 compilation data sets comprising of distance modulus of 580 SNIa supernovae at different redshifts, the Pantheon data set which contains Apparent magnitudes of 1048 SNIa supernovae at various redshifts and finally BAO data set of volume averaged distances at 5 redshifts. We employ the conventional Bayesian methodology to analyze the observational data and also the Markov Chain Monte Carlo (MCMC) technique to derive the posterior distributions of the parameters. The best fit values of Hubble parameter $H_0$ as per the four data sets are found as $61.53^{+0.453}_{-0.456}$, $ 69.270^{+0.229}_{-0.228}$, $78.116^ {+0.480}_{-0.479}$, and $ 71.318 ^{+2.473}_{-2.283}$ respectively. Off late the present value of Hubble parameters $H_0$ were empirically given as 73 and 67.7 (km/s)/Mpc using distance ladder techniques and measurements of the cosmic microwave background. The OHD+BAO+Union and ~OHD+Pan+BAO+Union combined data sets provide the best fit Hubble parameter value $H_0$ as $67.427^{+0.197}_{-0.199}$ and $74.997^{+0.143}_{-0.145}$ respectively. The various geometrical and physical properties of the model were also investigated and were found in good agreements with observations.

physics.gen-ph↗

arXiv2025

An oscillating Rastall universe crossing the phantom divide line

A cyclic flat universe with quintom behaviour and future big rip has been presented in the framework of Rastall gravity, which is an extension of the standard $Λ$CDM model. The Hubble parameter oscillates periodically between positive and negative values from one cycle to the next. Cosmic transit has been simulated through an oscillating time-dependent deceleration parameter, and is expected to occur at approximately $ 8.7~~ \text{Gyr}$. The causality is satisfied all the time except near the initial singularity and the future Big Rip singularity.The apparent horizon, entropy and other thermodynamical quantities associated to the current model have been analyzed. Energy conditions have been investigated.

gr-qc↗

arXiv2025

On the Field Theoretical Description of an Alternative Model to Generalized Chaplygin Gas and its Thermodynamic Behaviour

This paper investigates a newly proposed fluid description of dark energy within the framework of the late-time accelerated expansion of the universe. Our primary objective is to explore the theoretical foundation of the proposed equation of state by establishing its correspondence with well-known scalar field models such as quintessence, k-essence, and DBI-essence. Through this correspondence, we reconstruct key field parameters, including the scalar field $ϕ$ and scalar potential $V(ϕ)$, and analyze their evolutionary behavior across cosmic time. The study also evaluates the model's physical consistency and cosmological implications by examining fundamental energy conditions - Null Energy Condition (NEC), Dominant Energy Condition (DEC), and Strong Energy Condition (SEC). Furthermore, we conduct a comprehensive stability analysis to ensure the robustness of the model and investigate its thermodynamic properties, including possible phase transitions using entropy and Gibbs free energy. To assess the observational viability of the model, we compare its predictions against recent datasets, including Cosmic Chronometers (CC), Baryon Acoustic Oscillation (BAO), and Supernova Type Ia from the Pantheon+SH0ES compilation and Union 2.1, as well as recent DESI and DESY5 data. Our analysis demonstrates that the proposed fluid model aligns well with observational constraints, reproduces the late-time acceleration of the universe, and offers a compelling alternative to the standard $Λ$-CDM model while maintaining consistency with current data.

gr-qc↗

arXiv2025

Cosmological Implications of $f(R,Σ, T)$ Gravity: A Unified Approach Using OHD and SN Ia Data

This paper investigates the cosmological implications of the modified gravity framework known as $f(R,Σ, T)$ gravity, focusing on its potential to unify and extend current cosmological models. The theory, introduced by Bakry and Ibraheem in 2023, combines the Ricci scalar, a scalar parameter representing torsion or other geometric properties, and the trace of the energy-momentum tensor. By analyzing observational Hubble data (OHD) and the Pantheon compilation of Type Ia Supernovae (SN Ia), we explore how this framework provides the accelerated expansion of the universe, the nature of dark energy, and phenomena like the Big Rip singularity. Employing the Friedmann-Robertson-Walker (FRW) metric and solving the modified field equations, we derive key cosmological parameters such as the Hubble constant and matter energy density parameter. These parameters are constrained through statistical analysis of observational data, yielding and from OHD, and and from SN Ia. The evolution of the equation of state (EoS) parameter, isotropic pressure, and energy density is also investigated. By considering energy conditions and stability criteria, the study highlights the viability of gravity as an alternative framework to General Relativity and models. Our findings affirm the model's compatibility with current observational evidence and its potential to the universe's past and future dynamics.

gr-qc↗

arXiv2025

Dark Energy and Cosmic Evolution: A Study in f (R, T) Gravity

In the context of f(R, T) gravity theory for the flat Friedmann Lemaitre Robertson Walker (FLRW) model, the accelerating expansion of the universe is investigated using a specific form of the emergent Hubble parameter. Datasets from H(z), Type Ia supernovae (SNIa), and Baryon Acoustic Oscillations (BAO) are used to constrain the model and identify the ideal parameter values in order to evaluate the statistical significance of f(R, T) gravity. The best-fit parameters are derived by solving the modified Friedmann equations through a MCMC analysis. These parameters are used to compute the equation of state, statefinders, energy conditions, and the (w-w) plane. Furthermore, the evolution of kinematic cosmographic parameters is examined. The findings provide significant behavior and features of dark energy models. Our comprehension of the dynamics and evolution of the universe is improved by this study, which also advances our understanding of dark energy and how it shapes the universe.

gr-qc↗

arXiv2024

Properties of interacting quark star in light of Rastall gravity

This study explores the properties of quark stars (QS) formulated with an interacting quark matter equation of state (EoS) within the framework of Rastall gravity, a modified theory of gravity. We derive the mass-radius relationships and calculate the maximum gravitational masses and their corresponding radii, comparing these results under both Rastall gravity and general relativity. Our analysis incorporates recent observational data, including the GW190425 event, to constrain the model parameters ($\barλ, η, B_{\rm eff}$). We also assess the stability of these quark stars by evaluating their static stability, adiabatic index, and sound velocity profiles, thus confirming their viability within the modified gravitational framework.

gr-qc↗

arXiv2024

Probing Dark Energy Properties in $f Q,C)$ Gravity with FLRW Cosmological Models

This study delves into the cosmological implications of the $f(Q,C)$ modified gravity framework within the context of the FLRW spacetime which offers a dynamic alternative to the standard $Λ$CDM cosmology. Here, we define the transit form of Hubble's parameter to explain several geometrical and physical aspects. The chosen parametric form of the Hubble parameter represents a smooth transition from the decelerating early universe to the accelerating present and late-time evolution. Employing observational datasets such as the Hubble parameter, Type Ia supernovae, Baryon Acoustic Oscillations (BAO), and Standard Candles (SC), we constrain the model parameters using the Markov Chain Monte Carlo (MCMC) method. The isotropic pressure, energy density, equation of state parameter, and energy conditions were analyzed to explore the physical viability of the $f(Q,C)$ framework. The results highlight the model's ability to replicate key cosmological behaviors, including the accelerated expansion driven by dark energy.

gr-qc↗

arXiv2024

Anisotropic quark stars in $f(R,L_m,T)$ gravity

We investigate the impact of $f(R,L_m,T)$ gravity on the internal structure of compact stars, expecting this theory to manifest prominently in the high-density cores of such stars. In this study, we begin by considering the algebraic function $f(R,L_m,T) = R + αT L_m$, where $α$ represents the matter-geometry coupling constant. We specifically choose the matter Lagrangian density $L_m= -ρ$ to explore compact stars with anisotropic pressure. To this end, we employ the MIT bag model as an equation of state. We then numerically solve the hydrostatic equilibrium equations to obtain mass-radius relations for quark stars, examining static stability criteria, the adiabatic index, and the speed of sound. Finally, we use recent astrophysical data to constrain the coupling parameter $α$, which may lead to either larger or smaller masses for quark stars compared to their counterparts in general relativity.

gr-qc↗

arXiv2024

Probing Dark Energy Properties with Barrow Holographic Model in f(Q, C) Gravity

Understanding the accelerating expansion of the universe remains one of the foremost challenges in modern cosmology. This study investigates Barrow Holographic Dark Energy (BHDE), a model inspired by quantum gravitational corrections, within the framework of $f(Q,C)$ gravity. This extension of symmetric teleparallel gravity incorporates the non-metricity scalar $Q$ and the boundary term $C$, enabling a deeper exploration of cosmic dynamics without relying on a cosmological constant or exotic matter. The BHDE model is analyzed under a flat Friedmann-Robertson-Walker (FRW) metric, focusing on key cosmological parameters such as energy density, isotropic pressure, the equation of state (EoS) parameter, stability conditions and the energy conditions. The results demonstrate that the EoS parameter transitions from matter-like behavior ($z > 0$) to negative values at $z = 0$, indicating the dominance of dark energy and its role in the universe's accelerated expansion. As $z$ approaches $-1$, the EoS parameter asymptotically converges to $-1$, aligning with the $Λ$CDM model. This work underscores the potential of the BHDE model in $f(Q,C)$ gravity as a comprehensive framework for studying cosmic acceleration. By incorporating Barrow entropy and addressing the interplay between non-metricity and boundary terms, the model provides a dynamic approach to explaining dark energy.

gr-qc↗

arXiv2024

Properties of white dwarf with anisotropic pressure in Rainbow gravity

We investigate the properties of anisotropic white dwarf stars within the rainbow gravity adopting for matter content the Chandrasekhar model based on an ideal Fermi gas at zero temperature. We study in detail the effects of the anisotropic factor on stellar mass and radius, the speed of sound, and the relativistic adiabatic index in both radial and tangential directions. We find that causality is never violated, whereas the stability criterion based on the relativistic adiabatic index is not met when the objects are characterized by a positive anisotropic factor close to the Chandrasekhar limit. We present this significant observation here for the first time, to the best of our knowledge.

gr-qc↗

arXiv2024

Accretion Phenomena of Different Kinds of Chaplygin Gas Models onto Kehagias-Sfetsos Black Hole in Horava-Lifshitz Gravity Scenario

In the Horava Lifshitz gravity scenario, we have described the mass accretion process of a 4 dimensional Kehagias Sfetsos black hole caused by some candidates of dark energy in detail. Firstly, we have obtained the equation of mass for the black hole with respect to the cosmic scale parameter a in the Horava Lifshitz gravity framework. Then, one by one, we have considered dark energies like Generalized Cosmic Chaplygin gas, Variable Modified Chaplygin gas, New Variable Modified Chaplygin gas, Modified Chaplygin Jacobi gas, and Modified Chaplygin Abel gas, respectively, and established their equation of mass in terms of the redshift function z. In addition, we have presented the results with graphical representations of the mass and redshift functions. Finally, we came to the conclusion that, due to the accretion of all of the dark energy candidates mentioned above, the mass of a 4-dimensional Kehagias-Sfetsos Black Hole will increase gradually in correspondence to the evolution of the universe.

gr-qc↗

arXiv2024

Five-dimensional compact stars in Einstein-Gauss-Bonnet gravity

Within the framework of Einstein-Gauss-Bonnet theory in five-dimensional spacetime ($5D$ EGB), we derive the hydrostatic equilibrium equations and solve them numerically to obtain neutron stars for both isotropic and anisotropic distribution of matter. The mass-radius relations are obtained for SLy equation of state, which describes both the solid crust and the liquid core of neutron stars, and for a wide range of the Gauss-Bonnet coupling parameter $α$. More specifically, we find that the contribution of the Gauss-Bonnet term leads to substantial deviations from Einstein gravity. We also discuss that after a certain value of $α$, the theory admits higher maximum masses compared with general relativity, however, the causality condition is violated in the high-mass region. Finally, our results are compared with the recent observations data on mass-radius diagram.

gr-qc↗

arXiv2024

Exploring Phase Space Trajectories in $Λ$CDM Cosmology with f(G) Gravity Modifications

In this work, the cosmic solutions, particularly the well-known $Λ$CDM model, are investigated in the framework of the Gauss-Bonnet gravity, where the gravitational action incorporates the Gauss-Bonnet invariant function. We utilize a specialized formulation of the deceleration parameter in terms of the Hubble parameter $H$, given by $q = -1 - \frac{\dot{H}}{H^2}$, to solve the field equations. To identify the appropriate model parameters, we align them to the most recent observational datasets, which include 31 data points from the Cosmic Chronometers, Pantheon+, and BAO datasets. The physical characteristics of the cosmographic parameters, such as pressure and energy density, that correlate to the limited values of the model parameters, are examined. The evolution of the deceleration parameter suggests a transition from a decelerated to an accelerated phase of the universe. Additionally, we examine the stability of the assumed model and provide an explanation for late-time acceleration using the energy conditions. The behavior of the equation of state parameter has been analyzed through dynamical variables by constraining various parameters in light of the recent observational data. This study has resulted in a quintessence-like evolution.

gr-qc↗

arXiv2024

Logamediate inflation on the Swiss-cheese brane with varying cosmological constant

The existence of Schwarzchild black holes in the structure of Swiss-cheese brane-world led to the conclusion that this specific brane-world scenario is more realistic than the FLRW branes. In this paper, we show that a Logamediate inflation on the Swiss-cheese brane with time-dependent cosmological constant $Λ(H)$ leads to a positive kinetic term and a negative potential with AdS minimum. The cosmic pressure $p$ is always positive but the energy density $ρ$ starts to get negative after a finite time. However, there is a time interval where they both are positive. Although this behavior of $ρ$ can be considered as a drawback of Swiss-cheese brane where positive energy dominates the present universe, it has been suggested that the presence of some source of negative energy could have played a significant role in early cosmic expansion. The model suffers from the eternal inflation problem which appears from the evolution of the first slow-roll parameter $ε$. Due to the existence of $ρ^2$ term, we have tested the new nonlinear energy conditions. The slow-roll parameters have been investigated and compared to Planck 15 results.

gr-qc↗

arXiv2024

Barrow Holographic Dark Energy in f (Q, T) gravity

In the present analysis, we explore a new version of dark energy called Barrow holographic dark energy within the framework modified gravity called $f(Q,T)$ gravity by adopting the simple homogeneous, isotropic, and spatially flat Friedmann-Robertson-Walker (FRW) model of the universe. Our goal is to understand how the universe evolved over time. To do this, we use parameterizetion of Hubble's parameter method. We then use a powerful tool called Monte Carlo Markov Chain to find the best values for the constants in our formula. We do this by comparing our formula to actual data from observations of the universe. Once we have the best values for the constants, we calculate other important parameters that describe the universe's evolution. These include: Deceleration parameter which measures how quickly the expansion is slowing down. We found $q_0 = -0.601^{+0.0131}_{-0.0131}$. Equation of state parameter to measures the properties of dark energy. We find $ω_0 = -0.7018^{+0.0101}_{-0.0101}$. We also study the stability and energy conditions along with the state-finder and $O_m(z)$-parameter of our model to ensure it's consistent with our understanding of the universe.

gr-qc↗

arXiv2024

Cosmography in $f(Q,T)$ gravity with the specific $H(z)$

The dynamics of perfect fluid as a source in the context of modified gravity, specifically $f(Q,T)$ gravity, are examined within the Friedmann-Lemaître-Robertson-Walker (FLRW) cosmological model. This gravity is a generic function of the non-metricity scalar $Q$ and its trace $T$. We investigate the characteristics of the derived cosmological model using a parameterized form of Hubble's parameter, $H(z) = H_0\left[Ω_{0m}(1+z)^3 + (1-Ω_{0m})\right]^{\frac{1}{2}}$ (Mahmood et al. Int. J. Geom. Methods Mod. Phys., https://doi.org/10.1142/S0219887824502049). Our examination reveals how physical parameters such as energy density, pressure, and the equation of state parameter, among others, in our model accurately describe the physical behavior of the cosmos. Furthermore, we explore the kinematic parameters in our model, which provide valuable insights into the cosmos's expansion history, including its acceleration, deceleration, and the evolution of its large-scale structure. By exploring these aspects, we gain a deeper understanding of the cosmos's dynamics and evolution within the context of modified gravity.

gr-qc↗