arXiv subjects

Ujjal Debnath

Publications and source records attributed to Ujjal Debnath.

At least 37 records · Page 2Linked to original sources

arXiv2025

New Black Hole Solutions in f(P) Gravity and their Thermodynamic Nature

Black holes are the fascinating objects in the universe. They represent extreme deformations in spacetime geometry. Here, we construct f(P) gravity and the first example of static-spherically symmetric black hole solution in f(P) gravity and discuss their thermodynamics. Using the numerical approach and series solution, we discover the solution and demonstrate that it is a generalization of Schwarzschild. The solution is characterized by a single function that satisfies a nonlinear fourth order differential equation. Interestingly, we can analytically calculate the solution s specific heat, Wald entropy, and Hawking temperature as a function of horizon radius. After analyzing the specific heat, we discovered that the black hole is thermodynamically stable over a small horizon radius.

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arXiv2025

Observable Signatures of RN Black Holes with Dark Matter Halos via Strong Gravitational Lensing and Constraints from EHT Observations

We investigate the impact of dark matter halos on the gravitational lensing produced by electrically charged, spherically symmetric black holes in the strong-field regime. The study focuses on two dark matter models: the Universal Rotation Curve Model and the cold dark matter model. We derive the coefficients for the strong deflection limit and numerically analyze the deflection angle variations. Graphical representations of the results show that the strong deflection angle, $α_D$ , increases with the charge parameter $Q$ in the presence of a dark matter halo. We explore the astrophysical consequences for the supermassive black holes $M87^*$ and $SgrA^*$ , comparing the results with standard Reissner-Nordström and Schwarzschild black holes via strong gravitational lensing observations. Our findings suggest that charged black holes with dark matter halos can be differentiated from standard black holes. We constrain the charge parameter $Q$ using observational data from the Event Horizon Telescope Collaboration. For $M87^*$ , we find $0 \leq |Q| \leq 0.366M$ with the Universal Rotation Curve model and $0 \leq |Q| \leq 0.364M$ with the cold dark matter model. For $SgrA^*$ , the constraints are $0 \leq |Q| \leq 0.586M$ and $0 \leq |Q| \leq 0.584M$, respectively. These results suggest that charged black holes with dark matter halos satisfy the Event Horizon Telescope constraints, offering potential for future identification in observational campaigns.

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arXiv2024

Thermodynamics of Modified Chaplygin-Jacobi Gas and Modified Chaplygin-Abel Gas: Stability Analysis and Observational Constraints

This paper explores the thermodynamic properties and stability of two newly introduced gas models, namely the Modified Chaplygin-Jacobi gas and the Modified Chaplygin-Abel gas. To achieve this, we examine the behavior of relevant physical parameters to gain in depth information about the evolution of the universe. The specific heat formalism is employed to verify the applicability of the third law of thermodynamics. Furthermore, the equation of state for the thermal system is obtained by applying thermodynamic variables. The stability of the gas models is investigated within the framework of classical thermodynamics, focusing on adiabatic processes, specific heat capacities, and isothermal conditions. It is inferred that the proposed fluid configurations exhibit thermodynamic stability and undergo adiabatic expansion for suitable parameter choices. We then perform observational analysis using CC+BAO and Pantheon+SH0ES datasets to impose constraints on our model parameters using the Markov Chain Monte Carlo (MCMC) process.

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arXiv2024

Estimation of $H_0$ and $r_d$ in the $ω(z)$ Parameterization within Einstein and Horava-Lifshitz Gravity Using DESI-Y1 and SDSS-IV

We present a novel dynamical dark energy model within the frameworks of both Einstein gravity and Horava-Lifshitz gravity. Utilizing CDMMA parametrization of the dark energy equation of state $ω(z)$, we derive solutions to the field equations. By employing recent cosmological datasets, such as cosmic chronometer datasets, Type Ia Supernovae datasets, and Baryonic Oscillation datasets (DESI Y1 and SDSS-IV). We validate our model and determine optimal parameter values. Furthermore, we analyze the evolution of the Universe by showing the redshift dependence plots of key cosmological parameters through graphical representations. We also perform diagnostic analyses to compare our model with the standard model. Using the Akaike Information Criterion (AIC), we compare the three models and find that all of them are supported by the current data, making it impossible to discard any of them. Our model aligns well with recent observations and unveils intriguing features of the Universe, particularly the late-time behavior of the Universe.

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arXiv2024

Reconstructions of $f(\mathcal{P})$ and $f(\mathcal{Q})$ gravity models from $(m,n)$-type Barrow Holographic Dark Energy: Analysis and Observational Constraints

In this research, we have reconstructed the extended $f(\mathcal{P})$ cubic gravity and symmetric $f(\mathcal{Q})$ teleparallel gravity from the $(m,n)$-type Barrow Holographic Dark Energy (BHDE) model. We have derived the unknown functions $f(\mathcal{P})$ and $f(\mathcal{Q})$ in terms of $\mathcal{P}$ and $\mathcal{Q}$, assuming a flat, homogeneous, and isotropic universe. To constrain our model parameters, we employed cosmic chronometer datasets and Baryon Acoustic Oscillation datasets, utilizing Markov Chain Monte Carlo (MCMC) method. We analysed the behaviour and stability of each model throughout the universe's evolution by studying crucial parameters such as the deceleration parameter, equation of state (EoS) parameter $ω_{DE}$, density parameter $Ω(z)$ and the square of the speed of sound $v_s^2$. Additionally, we explored the cosmographic behaviour by plotting the jerk parameter, snap parameter, and lerk parameter against the redshift. Furthermore, we examined the $ω'_{DE}-ω_{DE}$ phase plane, the $(r,s^*)$, $(r,q)$ statefinder parameters, and the $Om(z)$ parameter offers profound revelations about the dynamics of the universe and the distinctive features of dark energy. Our analyses indicated that our model could produce a universe undergoing accelerated expansion with quintessence-type dark energy. These findings contribute to our understanding of the nature of dark energy and the evolution of the cosmos.

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arXiv2024

Study of Stable Dark Energy Stars in Hořava-Lifshitz gravity

We study the structure and basic physical properties of non-rotating dark energy stars in Ho$\Check{\text{r}}$ava-Lifshitz (HL) gravity. The interior of propsed stellar structure is made of isotropic matter obeys extended Chaplygin gas EoS. The structure equations representing the state of hydrostatic equilibrium i.e., generalize TOV equation in HL gravity is numerically solved by using chosen realistic EoS. Next, we investigate the deviation of physical features of dark energy stars in HL gravity as compared with general relativity (GR). Such investigation is depicted by varying a parameter $ω$, whereas for $ω\rightarrow \infty$ HL coincide with GR. As a results, we find that necessary features of our stellar structure are significantly affected by $ω$ in HL gravity specifically on the estimation of the maximum mass and corresponding predicted radius of the star. In conclusion, we can predict the existence of heavior massive dark energy stars in the context of HL gravity as compared with GR with not collapsing into a black hole. Moreover, we investigate the stability of our proposed stellar system. By integrating the modified perturbations equations in support of suitable boundary conditions at the center and the surface of the stellar object, we evaluate the frequencies and eigenfunctions corresponding to six lowest excited modes. Finally, we find that physically viable and stable dark energy stars can be successfully discussed in HL gravity by this study.

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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.

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arXiv2024

Observational Constraints on the Parameters of Hořava-Lifshitz Gravity

This study investigates the accelerated cosmic expansion within the Hořava-Lifshitz Model. To constrain the cosmological parameters of this model, we incorporate 17 Baryon Acoustic Oscillation points, 31 Cosmic Chronometer points, 40 Type Ia Supernovae points, 24 quasar Hubble diagram points, and 162 Gamma Ray Bursts points, along with the latest Hubble constant measurement (R22). We treat $r_{d}$ as a free parameter to extract $H_{0}$ and $r_{d}$ using late-time datasets, aiming for optimal fitting values in each model. Treating $r_{d}$ as free improves precision, reduces bias, and enhances dataset compatibility. The obtained values of $H_{0}$ and $r_{d}$ are compared to the $Λ$CDM model, showing consistency with previous estimates from Planck and SDSS studies. The Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) favor the Hořava-Lifshitz model, with the $Λ$CDM model having the lowest AIC. Additionally, we conduct $Δ$AIC and $Δ$BIC analyses to assess model preference.} Validation using the reduced $χ_{red}^{2}$ statistic indicates satisfactory fits for the Hořava-Lifshitz model, while recognizing $Λ$CDM as the preferred model. Extensions of the analysis warrant further investigation.

astro-ph.CO↗

arXiv2024

Addressing the $r_{d}$ Tension using Late-Time Observational Measurements in a Novel deceleration Parametrization

This paper introduces a novel cosmological model aimed at probing the accelerated expansion of the late Universe through a unique parametrization of the deceleration parameter. We aim to constrain key cosmic parameters by integrating recent measurements of the Hubble parameter obtained from various observational methods, including cosmic chronometers, Type Ia Supernovae, Gamma-Ray Bursts (GRB), Quasars, and Baryon Acoustic Oscillations (BAO) from recent galaxy surveys. With a redshift range spanning $0.106 < z < 2.33$ and incorporating the latest Hubble constant measurement from Riess in 2022, our analysis yields optimal fit values for the Hubble parameter $H_{0}$ and sound horizon $r_{d}$. Notably, we uncover an inconsistency in $H_{0}$ values derived from late-time observational measurements, reflecting the well-known $H_{0}$ tension. In terms of $r_{d}$, while there is close agreement between Joint analysis and Joint analysis with R22, discrepancies arise upon gradual inclusion of BAO and BAO with R22 datasets. Our model demonstrates excellent fit to observed data and aligns well with the standard $Λ$CDM paradigm at higher redshifts. However, its most intriguing aspect lies in predicting a super-accelerated expansion in the distant future, in contrast to the de Sitter phase predicted by $Λ$CDM. Additionally, unique behaviors in the jerk parameter hint at novel dynamics beyond traditional cosmological models. Statefinder and $O_{m}$ Diagnostics tests were conducted, and comparison using the Akaike information criterion indicates neither model can be ruled out based on the latest observational measurements. These findings propose our cosmological model as a compelling alternative to $Λ$CDM, offering fresh insights into dark energy's nature and the cosmos' future.

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arXiv2024

Constraining Cosmological Parameters with Viscous Modified Chaplygin Gas and Generalized Cosmic Chaplygin Gas Models in Horava-Lifshitz Gravity: Utilizing Late-time Datasets

This study examines accelerated cosmic expansion using the Viscous Modified Chaplygin Gas (VMMG) and Generalized Cosmic Chaplygin Gas (GCCM) within Horava-Lifshitz gravity. Our aim is to constrain essential cosmological parameters, such as the Hubble Parameter ($H_{0}$) and Sound Horizon ($r_{d}$). We utilize late-time datasets: 17 Baryon Acoustic Oscillation observations, 33 Cosmic Chronometer measurements, 40 Type Ia Supernovae data points, 24 quasar Hubble diagram data points, and 162 Gamma Ray Bursts data points, along with the latest determination of the Hubble constant (R22). Treating $r_{d}$ as a free parameter offers several advantages, including mitigating bias, enhancing precision, and improving compatibility with various datasets. By introducing random correlations in the covariance matrix during simulation, errors are effectively reduced. Our estimated values of the Hubble constant ($H_0$) and $r_{d}$ consistently align with measurements from both the Planck and SDSS experiments. Cosmographic tests provide valuable insights into the dynamics of various cosmological models, enriching our understanding of cosmic evolution. Statefinder diagnostics offer deeper insights into cosmic expansion dynamics, aiding in distinguishing between cosmological frameworks. Furthermore, the $o_{m}$ diagnostic test reveals that at late times, VMMG falls into the phantom region, while GCCM falls into the quintessence region. The Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) support all models, indicating plausible explanations. Notably, the $Λ$CDM model emerges with the lowest AIC score, suggesting its relatively superior fit. Validation via the reduced $χ_{\text{red}}^{2}$ statistic confirms satisfactory fits across all models, reinforcing their credibility.

astro-ph.CO↗

arXiv2024

Gravitational Lensing of Dark Energy Models and $Λ$CDM Using Observational data in Loop Quantum Cosmology

This paper investigates the accelerated cosmic expansion in the late Universe by examining two dark energy models, viscous modified Chaplygin gas (VsMCG) and variable modified Chaplygin gas (VMCG), within loop quantum cosmology alongside the $Λ$CDM model. The objective is to constrain cosmic parameters using the $Λ$CDM model and 30 of the latest $H(z)$ measurements from cosmic chronometers (CC), including Type Ia Supernovae, Gamma-Ray Bursts (GRB), Quasars, and 24 uncorrelated baryon acoustic oscillations (BAO) measurements across a redshift range from 0.106 to 2.33. The latest Hubble constant measurement from Riess in 2022 is included to enhance constraints. In the $Λ$CDM, VsMCG, and VMCG frameworks, best-fit parameters for the Hubble parameter ($H_0$) and sound horizon ($r_d$) are obtained. The results highlight significant disparities between $H_0$ and $r_d$ values from late-time observational measurements, reflecting the known $H_0$ and $r_d$ tensions. The gravitational lensing optical depth of the two dark energy models is studied by plotting $\log(τ(z_l)/H_0^{-3} τ_N)$ vs $z_l$. The probability of finding gravitational lenses (optical depth) in both models increases with lens redshift $z_l$. The change in optical depth behavior for different parameter constraints is graphically analyzed. A joint analysis of VsMCG and VMCG with $Λ$CDM is conducted. While the models diverge in the early Universe, they are indistinguishable at low redshift. Using the Akaike information criteria, the analysis indicates that neither dark energy model can be

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arXiv2024

Polytropic stellar structure in 5$\mathcal{D}$ Einstein-Gauss-Bonnet gravity

Polytropic stars are useful tools for learning about stellar structure without the complexity of comprehensive stellar models. These models rely on a certain power-law correlation between the star's pressure and density. This paper proposes a polytropic star model to investigate some new features in the context of $5\mathcal{D}$ Einstein-Gauss-Bonnet (EGB) gravity using the Finch-Skea {\em ansatz} [{\em M. R. Finch and J. E. Skea, Classical and Quantum Gravity 6, 467 (1989)}]. Analytical results are better described by graphical representations of the physical parameters for various values of the Gauss-Bonnet coupling constant $α$. The solution for a specific compact object, EXO 1785-248, with radius $\mathfrak{R} = 8.849_{-0.04}^{+0.04}$ km and mass $\mathcal{M} = 1.3 \pm 0.02~\mathcal{M}_{\odot}$, is shown here. We analyze the essential physical attributes of the star, which reveal the influence of the coupling parameter $α$ on the values of the parameters. Ultimately, we conclude that our current model is realistic because it satisfies all the physical criteria for an acceptable model.

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arXiv2024

Shadow and strong gravitational lensing of new wormhole solutions supported by embedding Class-I condition

This study deals with the new class of embedded wormhole solutions in the background of general relativity. Two newly calculated wormhole solutions satisfy all the required properties. All the energy conditions are discussed through their validity regions for the different ranges of involved parameters. In maximum regions, all energy conditions are violated. We investigate the shadow and strong gravitational lensing by the wormhole throat for the two new wormhole models, namely Model-I and Model-II. The present paper considers the wormhole throat to act as a photon sphere. We first derive null geodesics using the Hamilton-Jacobi separation method to investigate the shadow and strong gravitational lensing caused by the wormhole throat. We then numerically obtain the radius of wormhole shadow, strong deflection angle, and various lensing observables by taking the example of supermassive black M87* and Sgr A* in the context of both Model-I and Model-II. Keeping all other parameters fixed, it is observed that the parameters $ζ_1$ and $ζ_2$ for Model-I; and $χ_1$ and $χ_2$ for Model-II have significant effects on the wormhole shadow and strong gravitational lensing phenomena. Our conclusion is that it is possible to detect relativistic images, such as Einstein rings, produced by wormholes with throat radii of $r_{th}=3M$. Additionally, current technology enables us to test hypotheses related to astrophysical wormholes.

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arXiv2024

The estimation of parameters of generalized cosmic Chaplygin gas and viscous modified Chaplygin gas and Accretions around Black Hole in the background of Einstein-Aether gravity

In this paper, we have investigated the phenomenon of accelerated cosmic expansion in the late universe and the mass accretion process of a 4-dimensional Einstein-Aether black hole. Starting with the basics of Einstein-Aether gravity theory, we have first considered the field equations and two eminent models of Chaplygin gas, viz. generalized cosmic Chaplygin gas model and viscous modified Chaplygin gas model. Then, we obtained the energy density and Hubble parameters equations for these models in terms of some dimensionless density parameters and some unknown parameters. After finding the required parameters, we proceeded with the mass accretion process. For both models, we obtained the equation of mass in terms of the redshift function and represented the change of mass of the black hole graphically with redshift. At the same time, we have made a graphical comparison between the above-mentioned models and the $Λ$CDM model of the universe. Eventually, we have concluded that the mass of a 4-dimensional black hole will increase along the universe's evolution in the backdrop of Einstein-Aether gravity.

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arXiv2024

The effects of the pole dark energy on gravitational waves

In this paper, we have studied the effects of pole dark energy on the evolution of gravitational waves. The background evolution of gravitational waves in a flat FRW universe is considered and its dynamics are studied in the presence of pole dark energy. Two different potential functions are considered for the study. Using the field equations, we formulated the perturbed equations governing the evolution of gravitational waves with respect to redshift z within the background of the FRW Universe. Subsequently, we delved into the characteristics of gravitational waves for the pole dark energy model and reached interesting results.

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arXiv2024

On the entropy corrected thermal features of black holes

In this work, we investigate the thermal properties of black holes using a new class of generalized entropy functions [K. Ourabah, Class. Quantum Grav., 41, 015010 (2024)]. At the fundamental level, these entropic forms are associated with alternative gravitational laws, within an entropic gravity framework. Our investigation revolves around three distinct entropy functions associated with the Yukawa Potential Correction, Non-local Gravity Correction, and Gradient Field Gravity Correction. Through comparative analysis, we study how such entropic constructs impact the thermodynamic behavior of black holes. For each case, we derive the stability thermodynamic conditions associated with the respective entropic constructs.

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arXiv2024

Cosmological Test of Dark Energy Parametrizations in Horava-Lifshitz Gravity

In this work, we assume the FRLW Universe which is filled with dark matter along with dark energy in the framework of Horava-Lifshitz (HL) gravity. The dark energy is considered as the Linear (Model I) and CPL (Model II) parametrizations of the equation of state parameter. For both models, we express the Hubble parameter $H(z)$ in terms of the model parameters and redshift $z$. To rigorously constrain the model, we have employed a comprehensive set of recent observational datasets including cosmic chronometers (CC), Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), Gamma-ray Burst (GRB), Quasar (Q) and Cosmic Microwave Background Radiation (CMB). Through the joint analysis of this diverse collection of datasets, we have achieved tighter constraints on the model's parameters. This, in turn, allows us to delve into both the physical and geometrical aspects of the model with greater precision. Furthermore, our analysis has enabled us to determine the present values of crucial cosmological parameters, including $H_{0}$, $Ω_{m0}$, $Ω_{k0}$ and $Ω_{\Lambda0}$. It's noteworthy that our results are consistent with recent findings from Planck 2018, underscoring the reliability and relevance of our models in the current cosmological context. We also conduct analysis of cosmographic parameters and apply statefinder and diagnostic tests to explore the evolution of the Universe. In addition, the AIC and BIC suggest that the $Λ$CDM model is the preferred model among all our considered models. Our investigation into the models has unveiled intriguing features of the late universe

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arXiv2024

Constraints on the parameters of modified Chaplygin-Jacobi and modified Chaplygin-Abel gases in $f(T)$ gravity

In this study, we investigate two dark energy models, MCJG and MCAG, in the context of $f(T)$ gravity within a non-flat FLRW Universe. Our analysis considers radiation, dark matter, and dark energy components. We compare the equation of state for MCJG and MCAG with $f(T)$ gravity. Using recent astronomical data (e.g., $H(z)$, type Ia supernovae, Gamma Ray Bursts, quasars, and BAO), we constrain the models' parameters and explore the Universe's behavior. The reduced Hubble parameter is expressed in terms of observable parameters like $Ω_{r0}$, $Ω_{m0}$, $Ω_{k0}$, $Ω_{CJ0}$, $Ω_{CA0}$, and $H_0$. We investigate cosmic evolution using deceleration, $\mathrm{Om}$, and statefinder diagnostics. Information criteria are employed to assess model viability, comparing against the standard $Λ$CDM model. Our objective is to deepen our understanding of dark energy, its relation to $f(T)$ gravity, and the mechanisms governing the accelerated expansion of the Universe.

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