arXiv subjects

B. Mishra

Publications and source records attributed to B. Mishra.

At least 37 records · Page 2Linked to original sources

arXiv2025

Accelerating behavior from dynamical system analysis parameters

We have performed the dynamical system analysis to obtain the critical point in which, the value of the geometric and dynamical parameters satisfy the late-time cosmic behavior of the Universe. At the outset, the modified Friedmann equations have been reformulated into a system of coupled differential equations to ensure that the minimal set of equations required for a second-order $f(Q)$ gravity. Then these equations are solved numerically to constrain the parameters with Markov Chain Monte Carlo (MCMC) techniques. Cosmic Chronometers (CC) and high-precision Pantheon$^+$ Type Ia Supernovae datasets are used to constrain the parameters. The evolution of key cosmological parameters indicates that the model exhibits quintessence-like behavior at present, with a tendency to converge towards the $Λ$CDM model at late-times. The dynamic system analysis provided the critical points that correspond to different phases of the Universe, which are analyzed in detail. The existence of a stable de Sitter attractor confirms the accelerating behavior of the model.

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arXiv2025

Exploring Wormhole Structures within the Framework of $f(R,L_{m})$ Gravity

In this work, we investigate wormhole geometries within the framework of $f(R,\mathcal{L}_{m})$ gravity by considering a specific form of the model. From the corresponding field equations, the shape function is derived, and the traversability conditions are examined for suitable choices of the model parameters. The obtained shape function is shown to satisfy all the necessary requirements for a traversable wormhole, including the energy conditions. The geometric properties of the wormhole are analyzed in detail, and particular attention is given to the requirement that the proper radial distance $l(r)$ remains finite throughout the space-time, thereby ensuring the consistency of the geometry.

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arXiv2025

Effects of Matter Lagrangian in f(Q,T) Gravity: The Accelerating Cosmological Model

We investigate the logarithmic form of $f(Q,T)$ gravity with two different choices of matter Lagrangian such as: $\mathcal{L}_m = p$ and $\mathcal{L}_m = -ρ$. The parameters of the model has been constrained using Cosmic Chronometers (CC) in combination with DES-SN5YR and Pantheon$^+$ Type Ia supernova datasets. We have observed that the deceleration parameter shows a smooth transition from deceleration to acceleration phase and the effective equation of state parameter ($ω$) approaches to $-1$ at late times. The $Om(z)$ diagnostic exhibits a decreasing profile, confirming quintessence-like behavior, and the statefinder analysis demonstrates trajectories that remain near the $Λ$CDM fixed point but deviate into the quintessence region. The evolution of the density parameters satisfies the flatness condition, and the predicted age of the Universe lies within $t_0 \sim 13.7-14.3$ Gyr, consistent with CMB and stellar estimates. The findings indicate that the logarithmic model successfully reproduces the late-time accelerated expansion for both the choices of the matter Lagrangian.

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arXiv2025

Propagating Gravitational Waves in Teleparallel Gauss-Bonnet Gravity

Gravitational waves offer a key insight into the viability of classes of gravitational theories beyond general relativity. The observational constraints on their speed of propagation can provide strong constraints on generalized classes of broader gravitational frameworks. In this work, we reconsider the general class of Gauss-Bonnet theories in the context of teleparallel gravity, where the background geometry is expressed through torsion. We perform tensor perturbations on a flat FLRW background, and derive the gravitational wave propagation equation. We find that gravitational waves propagate at the speed of light in these classes of theories. We also derive the distance-duality relationship for radiation propagating in the gravitational wave and electromagnetic domains.

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arXiv2025

Exploring the Viability of $f(Q, T)$ Gravity: Constraining Parameters with Cosmological Observations

In this paper, we explore the model of $f(Q,T)$ gravity, an extension of symmetric teleparallel gravity where the nonmetricity scalar $Q$ is non-minimally coupled to the trace of the energy-momentum tensor $T$. To ensure general covariance and theoretical consistency, we adopt the covariant formulation of $f(Q, T)$ gravity, which allows a coordinate-independent treatment of the field equations and facilitates the correct identification of effective energy-momentum components. The model is developed as an alternative to the standard $Λ$CDM cosmological model and is analyzed using Cosmic Chronometer and Pantheon$^+$ supernovae datasets. Through Markov Chain Monte Carlo analysis, we constrain the model parameters $α$, $β$, and $H_0$, and compare the performance of the model with $Λ$CDM by evaluating statistical measures such as chi-square, Akaike information criterion (AIC), and Bayesian information criterion (BIC). The results show that the $f(Q, T)$ model effectively mimics $Λ$CDM while offering an alternative explanation based on modified gravity. We also examine cosmographic parameters like the deceleration parameter, confirming the transition of the Universe from deceleration to acceleration, and the violation of the strong energy condition, which aligns with observed late-time cosmic acceleration. Additionally, the model provides age estimates for the Universe that are consistent with current observations.

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arXiv2025

Late time behavior in $f(R,\mathcal{L}_{m})$ gravity through Gaussian reconstruction and dynamical stability

In this paper, we explore modified gravity in the framework of $f(R, \mathcal{L}_m)$ theories by reconstructing the function $f(\mathcal{L}_m)$, where $\mathcal{L}_m = ρ$ is the matter Lagrangian, under the assumption of a pressureless, matter-dominated Universe. Using a non-parametric Gaussian process reconstruction technique applied to Hubble data, we obtain two viable models of $f(\mathcal{L}_m)$ : (i) a power-law model $f_1(\mathcal{L}_m) = α\mathcal{L}_m^{b_1}$ with $b_1 \in [0.018, 0.025]$ and (ii) an exponential model $f_2(\mathcal{L}_m) = α\mathcal{L}_{m0} \left(1 - e^{-b_2 \sqrt{\mathcal{L}_m/\mathcal{L}_{m0}}} \right)$ with $b_2 \in [2.3, 3.0]$. We then fix the parameter values within these reconstructed ranges and analyze the corresponding dynamical systems within the matter-dominated epoch by constructing autonomous equations. Phase-space analysis reveals the presence of stable critical points in both models, suggesting viable cosmic evolution within their domains of validity. Both the models exhibit stable attractor solution at late time, reinforcing their viability in explaining the late time cosmic acceleration without explicitly invoking a cosmological constant. Our results indicate that $f(R, \mathcal{L}_m)$ gravity with data-driven matter-sector modifications can offer a compelling alternative description of cosmic dynamics during the matter-dominated era.

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arXiv2025

Late Time Phenomena in $f(T,\mathcal{T})$ Gravity Framework: Role of $H_0$ Priors

This study explored the behavior of the $f(T, \mathcal{T})$ cosmological model with the use of various data set combinations. We also compared the results for this model between the Pantheon+ (without SH0ES) and the Pantheon+\&SH0ES (with SH0ES) data sets. Additionally, we incorporated data from BAO along with $H_0$ priors. We observed that integrating SH0ES data points leads to a higher estimation of $H_0$ than Pantheon+ (without SH0ES). We perform an extensive MCMC analysis for each combination of data sets, providing constraints on the model parameters. We also computed the $χ^2_{min}$ value for each combination of data sets to evaluate the chosen model against the standard $Λ$CDM model. Our primary finding is that the various dataset combinations in the $f(T, \mathcal{T})$ model we examined relate to a range of Hubble constants, which could contribute to reducing the cosmic tension associated with this parameter. Additionally, we investigate the evolution of matter fluctuations by solving the density contrast evolution equation numerically. We calculate numerical solutions for the weighted growth rate $fσ_8$ using these findings. We plotted the cosmological background parameters to check the behavior of the $f(T, \mathcal{T})$ model in late-time. Based on the behavior of these background cosmological parameters, we conclude that our selected models reflect the late-time cosmic dynamics of the Universe.

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arXiv2025

The scalar-torsion gravity corrections in the first-order inflationary models

The corrections to the cosmological models induced by non-minimal coupling between scalar field and torsion are considered. To determine these corrections in explicit form, the power-law parametrization of these corrections are proposed. The estimates of possible influence of non-minimal coupling between scalar field and torsion on cosmological parameters for inflationary models implying linear relation between tensor-to-scalar ratio and spectral index of scalar perturbations are obtained. A procedure for verifying these inflationary models due to the observational constraints on the values of cosmological perturbation parameters is also considered.

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arXiv2025

Stable $f(Q)$ gravity model through non-trivial connection

This study effectively reconstructs a cosmological model utilizing covariant $f(Q)$ gravity within Connection-III and FLRW spacetime. The dynamic behavior of the reconstructed model is thoroughly analyzed using the Hubble parameter $H(z)$ and various observational datasets. Our robust findings demonstrate that the model displays quintessence behavior at the present epoch and converges to the $Λ$CDM model at late time. It is confirmed through comprehensive evaluations against energy conditions that the Null Energy Condition remains positive throughout cosmic evolution, and the Dominant Energy Condition is consistently satisfied. The Strong Energy Condition is initially fulfilled in the early Universe but violated in the late epoch. Moreover, scalar perturbations extensively assess stability, affirming the strength of the model with respect to the Hubble parameter. This research offers compelling insights into cosmic acceleration, suggesting that $f(Q)$ gravity can effectively displace the $Λ$CDM model and provides a convincing alternative explanation for the current accelerating expansion of the Universe without relying on the cosmological constant.

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arXiv2024

Stability of $f(Q, B)$ Gravity via Dynamical System Approach: a Comprehensive Bayesian Statistical Analysis

In this work, we explore the cosmological stability of $f(Q, B)$ gravity using a dynamical system approach, where $Q$ denotes the nonmetricity scalar and $B$ represents the boundary term. We determine the model parameters of $f(Q, B)$ through Bayesian statistical analysis, employing Markov Chain Monte Carlo techniques. This analysis incorporates numerical solutions and observational data from cosmic chronometers, the extended Pantheon$^+$ data set, and baryonic acoustic oscillation measurements. Our findings reveal a stable critical point within the dynamical system of the model, corresponding to the de Sitter phase, which is consistent with current observations of the Universe dominated by dark energy and undergoing late-time accelerated expansion. Additionally, we utilize Center Manifold Theory to examine the stability of this critical point, providing deeper insights into the behavior of the model. The cosmological implications of $f(Q, B)$ gravity indicate a smooth transition in the deceleration parameters from deceleration to the acceleration phase, underscoring the potential of the model to describe the evolution of the Universe. Our results suggests that the $f(Q, B)$ model presents a viable alternative to the standard $Λ$CDM model, effectively capturing the observed acceleration of the Universe and offering a robust framework for explaining the dynamics of cosmic expansion.

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arXiv2024

On static and rotating decoupled black holes without inner horizons

Through gravitational decoupling using the extended minimal geometric deformation, a new family of static and rotating ``hairy'' black holes is provided. The background of these models is a generic Schwarzschild metric containing as special cases, the Schwarzschild, Schwarzschild-dS, Reissner-Nordstrom and Reissner-Nordstrom-dS black holes. Assuming the Kerr-Schild condition and a general equation of state, the unknown matter sector is solved given rise to black hole space-times without a Cauchy horizon, transforming the original time-like singularity of the Reissner-Nordstrom and Reissner-Nordstrom-dS black holes into a space-like singularity. This fact is preserved for the rotating version of all these solutions.

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arXiv2024

Dynamical system analysis in modified Galileon cosmology

In this paper, we have investigated the phase space analysis in modified Galileon cosmology, where the Galileon term is considered a coupled scalar field, $F(ϕ)$. We focus on the exponential type function of $F(ϕ)$ and the three well-motivated potential functions $V(ϕ)$. We obtain the critical points of the autonomous system, along with their stability conditions and cosmological properties. The critical points of the autonomous system describe different phases of the Universe. In the results of our analysis, we have found the scaling solution for critical points, which determine different evolutionary eras for the Universe. The dark-energy-dominated critical points show stable behavior and indicate the Universe's late-time cosmic acceleration phase. Further, the results are examined with the cosmological data sets of the Hubble rate $H(z)$ and the Supernovae Ia.

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arXiv2024

Cosmology in modified $f(\mathcal{G})$ gravity: a late time cosmic phenomena

In this work, we present a method for numerically solving the Friedmann equations of modified $f(\mathcal{G})$ gravity in the presence of pressureless matter. This method enables us to predict the redshift behaviour of the Hubble expansion rate. To evaluate the credibility of the model, we applied a Bayesian MCMC technique using late-time cosmic observations to impose limitations on the free parameters of the Gauss-Bonnet model. Our results suggest that the $f(\mathcal{G})$ model can reproduce the low-redshift behaviour of the standard Lambda cold dark matter ($Λ$CDM) model, but there are significant differences at high redshifts, leading to the absence of a standard matter-dominated epoch. We also examined the profiles of cosmographic parameters using the model parameter values from the standard range to verify the intermediate epochs. Our analysis shows that the highly promising $f(\mathcal{G})$ model is a feasible candidate for explaining the current epochs. We presented a dynamical system analysis framework to examine the stability of the model. Our study identified critical points depicting various phases of the Universe and explained the evolutionary epochs. We demonstrated that the model effectively captures the evolution of energy components over cosmic time, supporting its validity as an alternate explanation for the observed acceleration of the Universe.

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arXiv2024

Non-minimally coupled teleparallel scalar field reconstruction of matter bounce scenario

Teleparallel description of gravity theories where the gravity is mediated through the tetrad field and consequent torsion provide an alternative route to explain the late time cosmic speed up issue. Generalization of the teleparallel gravity theory with different functional forms of the torsion scalar $T$ leads to $f(T)$ gravity. The role of scalar field played in addressing issues in cosmology and astrophysics has developed an interest in the inclusion of a scalar field along with an interaction potential in the action. Such a generalized gravity theory is dubbed as $f(T,ϕ)$ theory. We have explored such a gravity theory to reconstruct the interaction potential of the scalar field required for an extended matter bounce scenario. The cosmological implications of the reconstructed scalar field potential are studied considering two viable and well known functional forms of $f(T,ϕ)$. The energy conditions of these model are discussed to assess the viability of the cosmological models.

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arXiv2024

Teleparallel Gravity and Quintessence: The Role of Nonminimal Boundary Couplings

In this paper, we have outlined the development of an autonomous dynamical system within a general scalar-tensor gravity framework. This framework encompasses the overall structure of the non-minimally coupled scalar field functions for both the torsion scalar ($T$) and the boundary term ($B$). We have examined three well-motivated forms of potential functions and constrained the model parameters through dynamical system analysis. This analysis has played a crucial role in identifying cosmologically viable models. We have analysed the behaviour of dynamical parameters such as equation-of-state parameters for dark energy and the total, as well as all the standard density parameters for radiation, matter, and dark energy to assess their compatibility with current observational data. The phase space diagrams are presented to support the stability conditions of the corresponding critical points. The Universe is apparent in its late-time cosmic acceleration phase via the dark energy-dominated critical points. Additionally, we compare our findings with the most prevailing $Λ$CDM model. The outcomes are further inspected using the cosmological data sets of Supernovae Ia and the Hubble rate H(z).

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arXiv2024

Tracing cosmic evolution through Weyl-Type f(Q,T) gravity model: theoretical analysis and observational validation

We investigate the cosmic evolution of the Universe across different cosmological epochs in exponential Weyl-type $f(Q, T)$ gravity model. The theoretical analysis involves a detailed dynamical system approach, where we define dimensionless variables and derive a system of linear differential equations to identify critical points corresponding to the radiation, matter and de Siter phase. The findings show the transition from deceleration to acceleration phase, with stable and unstable critical points characterizing different phases of the evolution. In the second approach, we validate the theoretical predictions by using observational data from Cosmic Chronometers ($CC$) and $Pantheon^+$ datasets. We constrain the Hubble parameter and subsequently analysed the other cosmological and geometrical parameters. In this approach also, the transition from deceleration to acceleration has been confirmed, with the equation of state (EoS) parameter approaching $Λ$CDM at late times. The further validate this, we present the behaviour of state finder pair. We obtain the age of the Universe $13.81$ Gyr according to $CC$ data and $13.96$ Gyr with the $Pantheon^+$ dataset. The model behaviour in both the approaches shows strong agreement in the late-time behavior of the Universe. The evolutionary behaviour of Hubble parameter and distance modulus, reinforcing the reliability of the Weyl-type $f(Q, T)$ gravity model in describing the expansion history of Universe.

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arXiv2024

Matter Geometry Coupling and Casimir Wormhole Geometry

In this study, we investigate traversable wormhole solutions within the setup of $f(R,\mathcal{L}_{m})$ gravity, a modified theory of gravity where the gravitational action relies upon the matter Lagrangian $\mathcal{L}_{m}$ and the Ricci scalar $R$. In General Relativity (GR), stability issues in traversable wormholes necessitate the existence of exotic matter that violates the null energy condition (NEC). In contrast, we explore wormhole solutions that align with the criteria for Casimir wormholes, which do not necessarily require NEC violation. Our analysis demonstrates that in the context of $f(R,\mathcal{L}_{m})$ gravity, exotic matter can sustain these wormholes. We further examine the traversability conditions of the wormhole, considering both scenarios with and without the Generalized Uncertainty Principle (GUP) correction. Additionally, the stability of the wormhole is assessed based on equilibrium conditions. Our findings suggest that $f(R,\mathcal{L}_{m})$ gravity offers a viable framework for the existence of stable, traversable wormholes sustained by exotic matter, potentially expanding the landscape of viable wormhole solutions beyond the confines of GR.

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arXiv2024

Black Holes and Wormholes Beyond Classical General Relativity

In the paper, only Static Spherically Symmetric space-times in four dimensions are considered within modified gravity models. The non-singular static metrics, including black holes not admitting a de Sitter core in the center and traversable wormholes, are reconsidered within a class of higher-order $F(R)$, satisfying the constraints $F(0)=\frac{dF}{dR}(0)=0$. Furthermore, by making use of the so-called effective field theory formulation of gravity, the quantum corrections to Einstein-Hilbert's action due to higher-derivative terms related to curvature invariants are investigated. In particular, in the case of Einstein-Hilbert action plus cubic curvature Goroff-Sagnotti contribution, the second-order correction in the Goroff-Sagnotti coupling constant is computed. In general, it is shown that the effective metrics, namely Schwarzschild expression plus small quantum corrections, are related to black holes and not to traversable wormholes. In this framework, within the approximation considered, the resolution of singularity for $r=0$ is not accomplished. The related properties of these solutions are investigated.

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