arXiv subjects

Santosh V. Lohakare

Publications and source records attributed to Santosh V. Lohakare.

12 recordsLinked to original sources

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 $ω_{\rm eff}(z=0)\approx -0.664$ 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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arXiv2026

Cosmological implications of f(T, B) gravity: constraints from recent observations

In this work, we examine the theoretical framework of modified teleparallel gravity with the inclusion of the boundary term in the action and investigate its cosmological implications by considering the power-law model $f(T, B) = -T + α(-B)^β$, with the aim of addressing the late-time accelerated expansion and the dark energy. In this context, $T$ denotes the torsion scalar and $B$ represents the boundary term, whose presence allows for departures from standard teleparallel dynamics and provides a unified description that connects torsion and curvature-based formulations, reproducing $f(T)$ and $f(R)$ gravity in appropriate limits. The viability of the model is assessed by confronting its theoretical predictions with observational data while constraining the cosmological and model parameters through a Markov Chain Monte Carlo (MCMC) analysis using cosmic chronometers (CC), the Pantheon Plus sample (PPS), and the DESI baryon acoustic oscillation (BAO) Data Release 2 (DR2) datasets, and comparing its performance with the standard $Λ$CDM model. The Akaike Information Criterion (AIC) analysis shows that the combined CC+PPS dataset strongly favors the $f(T, B)$ model, suggesting an improved phenomenological fit to late-time observations relative to $Λ$CDM. Our result further shows an alleviation of H0 tensions, although a dedicated analysis is required to establish its full statistical significance. Furthermore, the background cosmological quantities indicate that the model exhibits a dynamical phantom-divide crossing while remaining consistent with late-time observations and yielding a viable expansion history and characteristic dark energy evolution.

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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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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 Cosmic Acceleration in Modified Gravity and Gauss-Bonnet Cosmology

This thesis focuses on late-time cosmic acceleration within modified theories of gravity, using various observational data sets and statistical analysis. The Universe is assumed to be spatially homogeneous and isotropic and is described by the Friedmann Lemaître Robertson Walker metric. The late-time acceleration of the Universe has posed a significant challenge to contemporary cosmology. General relativity addresses this by introducing the cosmological constant, forming the basis of the standard cosmological model ($Λ$CDM). However, this model has limitations, leading cosmologists to explore alternative explanations for late-time acceleration. These alternatives range from models involving a dynamic dark fluid known as dark energy, to large-scale modifications of gravitational interaction, known as modified gravity. The formulation of general relativity fundamentally changed our understanding of gravitation, redefining gravity as a manifestation of the curvature of spacetime rather than a force as described by Newton. Despite its success, general relativity has shown incompatibilities with observations, necessitating the introduction of dark matter and dark energy....

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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

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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arXiv2023

Observational constrained $F(R, \mathcal{G})$ gravity cosmological model and the dynamical system analysis

In this paper, we have analyzed the geometrical and dynamical parameters of $\mathcal{F}(R, \mathcal{G})=αR^2 \mathcal{G}^β$ cosmological model, ($R$, $\mathcal{G}$ being the Ricci scalar and Gauss-Bonnet invariant respectively), constraining the parameters through the cosmological data sets. It is exhibited that the model admits a viable radiation era, and early deceleration followed by late-time acceleration in the matter-dominated era. From the phase-space, portrait stability criterion has been analysed, restricting the parameter $β$, different from $β=-1$. Additionally, we have explored the stability of the model from the behavior of critical points and obtained the present value of the density parameter for matter-dominated and dark energy components, which are identical to those obtained through cosmological data sets.

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arXiv2023

Influence of three parameters on maximum mass and stability of strange star under linear $f(Q)-$action

This study simulates strange stars in $f(Q)$ gravity with an additional source under an electric field using gravitational decoupling and the complete Gravitational Decoupling (CGD) technique. By employing the Tolman ansatz and the MIT bag model equation of state (EOS), we explore bounded star configurations derived from the $θ_0^0 = ρ$ and $θ_1^1 = p_r$ sectors within the CGD formalism. Our models are subjected to physical viability tests, and we analyze the impact of anisotropy and the electric charge parameter $E_0$ as well as the coupling parameters $α$ and $β_1$. Comparisons are made with observational constraints, including GW190814, neutron stars PSR J1614-2230, PSR J1903+6620, Cen X-3 and LMC X-4. Notably, we achieve the presence of a lower "\textit{mass gap}" component by adjusting parameters $α$ and $β_1$. Our models exhibit well-behaved mass profiles, internal regularity, and stability, with the absence of gravitational collapse verified through the Buchdahl--Andréasson's limit. In addition, we present a detailed physical analysis based on three parameters, $α$ (decoupling strength), $β_1$ ($f(Q)$--coupling) and $Q$ (surface charge). This study provides insights into the behavior of compact objects in $f(Q)$ gravity and expands our understanding of strange star configurations within this framework.

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arXiv2022

Analyzing the geometrical and dynamical parameters of modified Teleparallel-Gauss-Bonnet model

To recreate the cosmological models, we employed the parametrization approach in modified teleparallel Gauss-Bonnet gravity. It has been interesting to apply the parametrization approach to investigate cosmological models. The real benefit of using this method is that the observational data may be incorporated to examine the cosmological models. Several cosmological parameters were examined, such as the Hubble parameter (H), the deceleration parameter (q), and the equation of state (EoS) parameter (w). The results obtained are consistent with recent cosmological findings in the conventional scenario. A transition scenario from a decelerating stage to an accelerating stage of cosmic evolution has been observed. The EoS parameter is also in the quintessence phase, which drives the accelerating expansion of the Universe. Also, we look at the violation of strong energy condition, which has become inevitable in the context of modified gravitational theory. Finally, we have performed the Om(z) diagnostic and also obtained the age of the Universe by using the data from the cosmological observations.

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arXiv2021

Cosmological model with time varying deceleration parameter in $F(R,G)$ gravity

In this paper, we study the dynamical behaviour of the Universe in the $F(R,G)$ theory of gravity, where $R$ and $G$ respectively denote the Ricci scalar and Gauss-Bonnet invariant. Our wide analysis encompasses the energy conditions, cosmographic parameters, $Om(z)$ diagnostic, stability and the viability of reconstructing the referred model through a scalar field formalism. The model obtained here shows the quintessence like behaviour at late times.

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