arXiv subjects

B. Mishra

Publications and source records attributed to B. Mishra.

At least 19 recordsLinked to original sources

arXiv2026

Dark Matter Admixed Quark Stars: A Relativistic Two-Fluid Approach

In this paper, we examine the stellar properties of quark stars containing dark matter, focusing on both non-rotating and slowly rotating configurations. By employing a two-fluid framework, we formulate the generalized Tolman--Oppenheimer--Volkoff equations, treating dark matter and ordinary matter as independent perfect fluids that interact solely through gravitational forces. We model ordinary matter using the color-flavor-locked and the MIT bag model equation of state, while for dark matter, we apply a self-interacting bosonic condensate along with fermionic equation of state. By considering a dark matter fraction of $f_\x=5\%$ and varying the bag constant for ordinary matter, we investigate how dark matter accumulation affects global stellar features such as maximum gravitational mass, radius, and dimensionless tidal deformability. Further, we extend our analysis to first-order rotational effects, calculating the frame-dragging equation and the influence of moments of inertia on the two-fluid system. We also explore universal relations, particularly the connection between rotation and tidal effects, to understand how the inclusion of dark matter affects the relationship between rotational and the tidal deformability. Our findings indicate that a dark matter fraction of $f_\x=5\%$ can lead to notable deviations from the traditional single-fluid quark star characteristics in stellar radius, gravitational mass and tidal deformability. Moreover, the response to rotational and tidal forces remains consistent even in the inclusion of the dark matter component. Finally, we compare our theoretical results with current observational data from GW events and the NICER mission, thereby demonstrating that our developed two-fluid models are consistent with these observations.

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arXiv2026

Corrections to inflationary models induced by non-minimal coupling between scalar field and curvature

In this paper, we consider possible corrections to the characteristics of inflationary models based on a specific parametrization of the non-minimal coupling between the scalar field and curvature. At the inflationary stage, these corrections lead to a deformation of the scalar field potential and a corresponding deviation in the determination of the cosmological perturbation parameters. At the same time, it is shown that the proposed parametrization yields a description of the reheating stage dynamics completely analogous to the case of Einstein gravity with minimal coupling between the scalar field and curvature. For a model-independent analysis of inflationary corrections induced by a non-minimal coupling, a classification of inflationary scenarios based on the expansion in series of the dependence of the tensor-to-scalar ratio on the spectral index of scalar perturbations is considered. It is also shown that this approach allows for the inclusion of well-known inflationary models as special cases.

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arXiv2026

Einstein--Gauss--Bonnet Inflationary Cosmology in Phase-$\theta$ Formalism

A central challenge in testing inflationary scenarios with cosmic microwave background (CMB) data is to derive predictions for cosmological observables that remain accurate beyond the slow-roll regime, where the standard consistency relations are no longer applicable. We address this issue in the context of Einstein--Gauss--Bonnet (EGB) gravity by introducing a phase-$\theta$ parametrization of the inflationary dynamics. Within this framework, the background evolution and the coefficients governing scalar and tensor perturbations are expressed entirely in terms of a single monotonic phase variable and the Hubble parameter. This construction provides a closed, analytical mapping between the background parameters of a given model and the associated inflationary observables. A notable advantage of the proposed parametrization is that it remains regular throughout the inflationary epoch, including the end-of-inflation regime, in which the conventional slow-roll consistency relations no longer hold. As an illustrative application, we consider a Starobinsky-type potential supplemented by a linear coupling between the inflaton and the Gauss--Bonnet invariant. Using the proposed formalism, we demonstrate that the resulting predictions of the Starobinsky model are consistent with the most recent constraints from ACT DR6 and BICEP/Keck, explicitly incorporating the impact of the non-minimal Gauss--Bonnet coupling on the expected values of the cosmological perturbation parameters. Finally, we compute the corresponding relic stochastic gravitational-wave background and evaluate its detectability with current and forthcoming gravitational-wave observatories.

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arXiv2026

Non-Metricity Corrections Approach to Alleviate $H _0$ Tension: The Logarithmic and Nonlinear $f(Q)$ Models

The persistent discrepancy between early-time and late-Universe measurements of the Hubble constant commonly known as the $H_0$ tension remains one of the most pressing open questions in modern cosmology. In this work, we explore whether modifications to the gravitational sector, specifically within the framework of symmetric teleparallel gravity, can offer a viable pathway toward alleviating this tension. We consider two functional forms of $f(Q)$ gravity: a logarithmic model and a nonlinear saturation model, both of which introduce geometric corrections to the standard expansion history without invoking a cosmological constant. Constraining these models through a Bayesian MCMC analysis against a comprehensive suite of observational data, including cosmic chronometers, Type Ia supernova compilations (Pantheon, Pantheon$+$SH0ES, and DES SN5YR), and BAO measurements from SDSS and DESI, we find that both models remain statistically competitive with $\Lambda$CDM. The logarithmic model, in particular, consistently infers intermediate values of $H_0$ between the \textit{Planck} and SH0ES benchmarks across all dataset combinations, and carries lower AIC and BIC penalties, establishing it as the more promising candidate for partially easing the $H_0$ tension within a modified gravity framework.

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arXiv2026

Late-Time Cosmic Acceleration in Ricci-Gauss-Bonnet Gravity via Gradient Descent Optimization

We study the late-time evolution of the Universe within the f(R,G) gravity framework, where R is the Ricci scalar and G is the Gauss-Bonnet term. To make the model tractable, we propose a parametrization scheme and determine its parameters using Gradient Descent, with constraints coming from the latest Cosmic Chronometer (CC) and Pantheon+ supernova data. Key cosmological indicators, namely the deceleration parameter q and the equation-of-state parameter w, show a clear transition from past deceleration to the present accelerated expansion. Interestingly, the equation-of-state parameter w remains above the phantom divide, indicating quintessence-like behavior consistent with current observations. Energy-condition analysis further supports this framework: the strong energy condition is violated, consistent with models allowing cosmic acceleration, whereas both the weak and null energy conditions remain satisfied. To test consistency, we also apply the Om(z) diagnostic, which distinguishes this model from the standard cosmological constant scenario and indicates a quintessence-dominated future evolution. Using the best-fit values, we estimate the age of the Universe, obtaining good agreement with independent astrophysical measurements. Overall, the results suggest that f(R,G) gravity provides a viable and self-consistent explanation for late-time cosmic acceleration when constrained using the combined CC and Pantheon+ datasets.

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arXiv2026

Cosmological Parameters in $f(T)$ Gravity: Theoretical and Observational Analysis

The $f(T)$ gravity is one of the extensions of teleparallel equivalent of general relativity, in which more general functions of the torsion scalar $T$ can be described. With the proposed functional form of $f(T) = \alpha T - \beta u^{-n} + \gamma u^m$, where $u = (-T/6)$, we have analyzed the cosmological parameters using dynamical system analysis and cosmological datasets. The dynamical behavior of this model is analyzed with phase-space analysis by transforming the cosmological equations into an autonomous system. Critical points are identified, and their stability conditions examined, enabling the classifications of the early and late-time evolutionary phases of the Universe. The stability conditions are further demonstrated by phase-portrait diagrams that highlight transitions between radiation, matter, and dark-energy-dominated epochs. Then we used the Markov Chain Monte Carlo statistical technique to constrain the model parameters with the recent observational dataset, such as DESI DR2 BAO, and its combination with the Hubble and Pantheon+SH0ES data. The best-fit values for the model parameters were obtained by data analysis, $m \equiv 0.91^{+0.07}_{-0.09}$ and $n \equiv 0.69^{+0.09}_{-0.08}$, and are well within the stability range obtained ($m<1\land n>-1$) through dynamical system analysis. The combined theoretical and observational analysis shows that the proposed $f(T)$ gravity model successfully reproduces the observed cosmic expansion history of the Universe.

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arXiv2026

Accelerating Cosmological Model with Scalar Field in $f(R,\mathcal{L}_{m})$ Gravity

In this work, we investigate the cosmological dynamics of $f(R,\mathcal{L}_m)$ gravity using two complementary scenarios: without a scalar field and with a minimally coupled generalized scalar field. For the case without a scalar field, we consider a functional form with linear and exponential dependence on the matter Lagrangian and perform a dynamical system analysis. The resulting autonomous system admits a matter-dominated saddle configuration and a de Sitter attractor . Due to the non-hyperbolic nature of the critical curves, Center Manifold Theory (CMT) is employed to establish the local asymptotic stability of the de Sitter solution. We then extend the framework by including a minimally coupled generalized scalar field with an exponential self-interacting potential. The extended autonomous system also contains a matter-dominated saddle point and a stable dark-energy-dominated attractor corresponding to a late-time de Sitter phase. The stability of the attractor is confirmed through CMT, and the evolution of the cosmological parameters demonstrates a smooth transition from a matter-dominated decelerating era to accelerated. Also, in the absence of the scalar field, the matter-dominated configuration associated with a vanishing nonlinear contribution remains stable, whereas the inclusion of the scalar field transforms the matter era into a saddle configuration, thereby enabling the Universe to naturally evolve toward the late-time accelerated attractor. In both scenarios, the exponential power term equal to $-1$ corresponds to a late-time de Sitter phase. These results show that both scenarios lead to late-time cosmic acceleration, while the inclusion of the scalar field provides an additional dynamical mechanism for realizing a stable dark-energy-dominated Universe without invoking a cosmological constant.

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arXiv2026

Growth factor in teleparallel Gauss-Bonnet gravity

Teleparallel gravity offers a competing geometric framework on which to build cosmological models. The Gauss-Bonnet invariant captures key aspects of the underlying geometry that has been shown to be an interesting way to form cosmological models beyond $\Lambda$CDM cosmology. In this work, we explore three competing cosmological models in $F(T,T_G)$ cosmology in the context of their evolution of the growth of structure in the Universe. This is a core test of the viability of any cosmological model. In our work, we show how these models are qualitatively competitive with $\Lambda$CDM cosmology for certain ranges of model parameters. Interestingly, the models can arrive at the same level of growth as $\Lambda$CDM while producing possible deviations at intermediate scales.

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arXiv2026

Implications of Matter--Curvature Coupled Gravity on Chandrasekhar Mass Limit of White Dwarfs

We investigate white dwarfs in the framework of f(R,Lm) and f(R,Lm,T) gravity to explore the Chandrasekhar limit. We have considered two functional forms of f(R,Lm) and one functional form of f(R,Lm,T) gravity. Considering the matter Lagrangian Lm=p , we calculate modified TOV equations for each of the forms. By employing the fully degenerate electron gas equation of state in the modified ToV equations, we derive the mass-radius relation for each functional form of both f(R,Lm) and f(R,Lm,T) gravity. Our models imply modifications in the Chandrasekhar mass limit that deviate significantly from the GR and the Newtonian cases. In the f(R,Lm,T) gravity, the new mass limit of the white dwarf can reach up to 1.537M while in f(R,Lm,T) with the quadratic extension can reach up to 1.52M and with square-root exponential model extension up to 2.08M. Further, we analyze the static stability criterion, the gravitational redshift, and the adiabatic indices. For the power-law form of f(R,Lm) and the nonlinear form of f(R,Lm,T) gravity, significant variations are observed at higher densities rho_c>1010gcm^-3, while substantial changes are noted at much lower central densities in the case of square-root exponential model form of f(R,Lm) gravity. The higher-density configurations should be regarded as formal equilibrium solutions within the adopted Chandrasekhar EoS and not as fully realistic stable C-O WDs, since additional high-density microphysics has not been included. We also calculate compactness and gravitational redshift, which are much lower than those of NS and BH. The configuration satisfies the adiabatic stability criterion, which shows that all considered models yield Gamma > 4/3 throughout the interiors of WDs. Overall, our models provide a viable framework for the existence of superChandrasekhar mass limit, extending beyond the classical predictions in the Newtonian and/or GR cases.

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arXiv2026

Evolutionary Phase of Universe in $f(R,L_m,T)$ Gravity: The Dynamical System Analysis

In this paper, the dynamical system analysis has been performed to analyze the dynamical behavior of the Universe in $f(R,L_m,T)$ gravity with a scalar field. A well motivated potential function and the linear form of the functional $f(R,L_m,T)$ have been incorporated into the Friedmann equation, and the autonomous dynamical system has been framed by introducing dimensionless variables. The stability behavior of the critical points is obtained and analyzed based on their corresponding eigenvalues. Moreover, cosmological parameters such as the deceleration parameter and the dynamical parameters such as equation of state and density parameters are obtained using the dimensionless variables. It has been observed that the system provides critical points that describe different evolutionary phases of the Universe.

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arXiv2026

Hubble Tension and Dark Energy in Teleparallel Gauss-Bonnet Gravity: New Constraints from DESI BAO, Pantheon$^+$ and Hubble Data

We explore the cosmological dynamics of a teleparallel Gauss-Bonnet gravity model defined by the torsion scalar $T$ and the torsion-based Gauss-Bonnet invariant $T_{\mathcal{G}}$, deriving modified Friedmann equations for a flat FLRW Universe and corresponding linear scalar perturbation equations. Using a numerical approach, we solve these equations for pressureless matter, predicting the redshift evolution of the Hubble parameter $H(z)$. Using a Bayesian Markov chain Monte Carlo analysis based on late-time observations from Cosmic Chronometers, Pantheon$^+$ without SH0ES, and DESI BAO Data Release 1 and Data Release 2, we constrain the model parameters and show that this class of $f(T,T_\mathcal{G})$ cosmologies can mimic an effective dark-energy component without introducing an explicit cosmological constant. We further examine the scalar perturbation sector of the posterior-supported cosmological branch and find that the solutions considered in this work remain well-behaved within the adopted perturbative treatment. The model yields a present-day effective equation-of-state parameter in the range $\omega_{\rm eff}(z=0)\approx -0.664$ to $-0.693$, consistent with late-time observations, and shifts the inferred value of $H_0$ toward $69$--$71.5\ {\rm km\,s^{-1}\,Mpc^{-1}}$, suggesting a partial alleviation, though not a complete resolution, of the Hubble tension.

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arXiv2025

Reconstructing $f(T)$ Gravity From Hubble Parameterization Constraints

In this paper, we have presented the cosmological model of the Universe that represents late time cosmic acceleration in torsion based gravitational theory, the $f(T)$ gravity. A well motivated parametrization for the Hubble parameter has been introduced and the free parameters involved are constrained using the cosmological datasets. With the constrained values of the free parameters, other geometrical parameters such as deceleration parameter, jerk parameter, and snap parameter are analyzed and confronted with the prescribed value of the cosmological observations. In addition, the dynamical parameters are analyzed in some non-linear form of $f(T)$ and the energy conditions are also studied and confirmed with the violation of the strong energy condition. The obtained cosmological model provides late time phantom behavior of the Universe.

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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 $\Lambda$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 $\mathcal{L}_m = -\rho$. 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 ($\omega$) 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 $\Lambda$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

Gauge invariant perturbations of $F(T,T_G)$ Cosmology

The Gauss-Bonnet invariant connects foundational aspects of geometry with physical phenomena in a variety of ways. Teleparallel gravity offers a novel direction in which to use the Gauss-Bonnet invariant to go beyond standard cosmology. In this work, we explore the cosmological perturbations of teleparallel gravity generalized through the Gauss-Bonnet invariant. This is crucial in understanding the viability of these models beyond background analyses. We do this by taking a gauge invariant approach, which is followed by popular gauge choice examples. It is important to take this approach to understand the stability and healthiness of the underlying theory. We determine the equations of motion for all perturbative modes and offer a physical interpretation for the new contributions for each of the modes.

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arXiv2025

Logarithmic and Strong Coupling Models in Weyl-Type $f(Q,T)$ Gravity

In this paper, we have explored the cosmological implications of Weyl-type $f(Q,T)$ gravity, a modified gravitational theory formulated from Weyl geometry. The nonmetricity scalar $Q$ is coupled to the trace $T$ of the energy-momentum tensor. We analyze two models based on the logarithmic and strong coupling form of the function $f(Q,T)$. The corresponding field equations are then solved numerically after reformulating the system in terms of redshift. We used combined dataset from Cosmic Chronometers (CC), Pantheon$^+$ supernovae, and Baryon Acoustic Oscillations (BAO) and performed the Markov Chain Monte Carlo (MCMC) analysis to constrain the model parameters. Using the constrained parameters, the geometrical and dynamical aspects of the models are analyzed. The results successfully describe a transition from decelerated to accelerated expansion for both the models. The models mostly exhibit quintessence-like behavior and asymptotically approach the $\Lambda$CDM scenario at late times. The calculated age of the Universe from each model aligns with constraints from Planck and stellar age data. The violation of the strong energy condition and the satisfaction of null energy condition and dominant energy conditions are shown.

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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 $\mathcal{L}_m = \rho$ 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 $f_1(\mathcal{L}_m) = \alpha \mathcal{L}_m^{b_1}$ with $b_1 \in [0.018, 0.025]$ and (ii) an exponential model $f_2(\mathcal{L}_m) = \alpha \mathcal{L}_{m0} \left(1 - e^{-b_2 \sqrt{\mathcal{L}_m/\mathcal{L}_{m0}}} \right)$ 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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