arXiv subjects

M. S. Barak

Publications and source records attributed to M. S. Barak.

12 recordsLinked to original sources

arXiv2026

Hu-Sawicki $f(R)$ Gravity in a Non-Flat Universe: Constraints from DESI-DR2, BBN, and Type Ia Supernovae

Late-time cosmic acceleration is conventionally ascribed to a cosmological constant, though $Λ$CDM continues to face several theoretical difficulties that keep alternative gravity models under active consideration. This work examines the Hu-Sawicki $f(R)$ model in a spatially non-flat background, with the modified-gravity parameter $b$ and the curvature density $Ω_k$ both treated as free parameters, constrained using DESI-DR2 BAO, BBN, and four Type Ia supernova compilations -- PantheonPlus, PantheonPlus+SH0ES, Union3, and DESY5yr. Across all four combinations, $H_0$ and $Ω_m$ stay close to their $Λ$CDM values, with a noticeable shift in $H_0$ appearing only for the SH0ES-calibrated dataset. The parameter $b$ departs from zero at better than $2σ$ in three of the four fits, most prominently for DESY5yr, whereas the SH0ES-calibrated combination alone prefers $b<0$. A strong positive correlation among $b$, $H_0$, and $Ω_k$ underlies this shift, suggesting that curvature signatures obtained under $Λ$CDM can be reabsorbed into the modified-gravity sector once this additional freedom is allowed. Statistical model comparison via AIC and BIC gives a mixed picture: AIC leans toward the Hu-Sawicki model in three of the four combinations, while BIC's heavier penalty on the extra parameter favors $Λ$CDM in most cases, and only DESY5yr is preferred under both criteria. These findings show that the Hu-Sawicki $f(R)$ scenario with unconstrained curvature is nonetheless a statistically feasible, if not obviously preferred, alternative to $Λ$CDM, and that curvature restrictions generated inside $Λ$CDM cannot be viewed as independent of the underlying gravity model.

gr-qc↗

arXiv2026

Testing a Sign-Switch Cosmological Model with Curvature through Latest Planck 2018, DESI DR2 and PantheonPlus\&SH0ES Observational Data

We investigate the spatial geometry of the Universe within the framework of a sign-switch dark energy scenario by extending the recently proposed $Λ_{\rm s}$CDM model to include a free curvature parameter $Ω_k$.In this framework, the effective cosmological constant undergoes a transition from a negative to a positive value at a characteristic redshift $z_{\dagger}$. Using the latest Planck 2018 cosmic microwave background (CMB) data, DESI DR2 baryon acoustic oscillation (BAO) measurements, and the PantheonPlus\&SH0ES Type Ia supernova sample, we derive joint constraints on the spatial curvature parameter $Ω_k$ and other cosmological parameters. We find that Planck data itself slightly favors a closed universe within both the $Λ_{\rm s}$CDM$+Ω_k$ and $Λ$CDM$+Ω_k$ frameworks, although spatial flatness remains well within the allowed uncertainties. When low-redshift probes were included, the curvature constraints were significantly tightened. In particular, the full Pk18+DR2+PP\&SH0ES dataset yields $Ω_k = 0.0001 \pm 0.0014$ for the $Λ_{\rm s}$CDM model, indicating a universe that is remarkably consistent with spatial flatness. We further analyzed the correlations between $Ω_k$, $H_0$, and $S_8$, finding that the inclusion of curvature and a sign-switch dark energy component helps stabilize cosmological parameter estimates while remaining compatible with current observational constraints. Model comparison using AIC and Bayesian evidence shows that the $Λ_{\rm s}$CDM model receives inconclusive/weak observational support relative to $Λ$CDM.

astro-ph.CO↗

arXiv2026

Testing Exponential $f(R)$ Gravity with CMB, DESI-DR2, and Supernova Data

One of the most popular competitors to the CDM paradigm as an explanation for the late-time acceleration of the universe is the modification of general relativity (GR), with models such as $f(R)$ gravity among the main motivations. In this study, we consider an exponential $f(R)$ gravity model as a possible extensions of the GR. The extra scalar degrees of freedom and their effects on the cosmic expansion and structure formation are continuously considered in this scenario. By combining the PPS, BBN, CC, DESI-DR2, and CMB datasets, we imposed limitations on this model. We performed a detailed statistical analysis of the free model parameter $b$ together with the standard cosmological parameters. Our analysis yields values of $H_0$ that are slightly lower than those obtained in $Λ$CDM, indicating no significant relaxation of the $H_0$ tension. In contrast, the model predicts systematically higher values of $S_8$, leading to a moderate alleviation of the $S_8$ tension by up to $\sim 1.2σ$ when late-time datasets are included. Overall, these results demonstrate that although the considered $f(R)$ gravity model does not resolve all cosmological tensions simultaneously, it provides a consistent improvement in the description of large-scale structure formation.

gr-qc↗

arXiv2026

Alleviating the Hubble Tension with Logarithmic Dark Energy: Constraints on the $w_{log}$CDM Model

Observational constraints are considered on a $w_{log}$CDM model of the dark energy equation of state, $w_{d}(z) = w_{0} + w_{a}\left( \frac{\ln(2+z)}{1+z} - \ln 2 \right)$, using the most recent cosmological datasets including DESI Baryon Acoustic Oscillation (BAO) measurements, Big Bang Nucleosynthesis (BBN) priors, Cosmic Chronometer (CC) observations, and Pantheon Plus (PPS) Type Ia supernovae. From the combined DESI BAO+BBN+CC+PPS dataset, we obtain $H_0 = 71.02 \pm 0.66~\text{kms}^{-1}\text{Mpc}^{-1}$, $Ω_m = 0.2863 \pm 0.0080,$ $w_0 = -0.875 \pm 0.066,$ $w_a = -0.69^{+0.37}_{-0.32},$ at the 68\% and 95\% confidence levels, indicating a preference for phantom dark energy with mild evidence for temporal evolution. The Hubble constant obtained from our model is closer to the local SH0ES measurement than the standard $Λ$CDM prediction, partially easing the Hubble tension. We perform extensive parameter-space exploration revealing correlations between $w_0$, $w_a$, and $H_0$, showing that dynamical dark energy models can fit higher values of the Hubble constant. The reconstructed deceleration parameter $q(z)$ shows the transition from deceleration to acceleration at $z \sim 0.6$--$0.7$, while the equation-of-state reconstruction remains consistent with a cosmological constant across the observed redshift range. A model comparison using information criteria indicates that the $w_{log}$CDM model remains statistically competitive with $Λ$CDM.

physics.gen-ph↗

arXiv2026

Observational Constraints and Geometric Diagnostics of Barboza-Alcaniz and Logarithmic Dark Energy Parametrizations

This study investigates and compares two prominent two-dimensional dark energy (DE) parameterizations: Barboza-Alcaniz (BA) and Logarithmic forms by comparing them with a comprehensive set of observational data comprising Type Ia Supernovae (SNe Ia) from the Pantheon compilation, Baryon Acoustic Oscillations (DESI BAO), and Cosmic Chronometers (CC). The primary objective was to explore the constraining power and cosmological implications of each parameterization in light of the current data. After formulating the theoretical framework and background equations governing cosmic expansion, we employ Markov Chain Monte Carlo (MCMC) techniques using the emcee Python package to constrain the free parameters of each model. The best-fit values for parameters $ω_0$, $ω_a$, and $H_0$ were extracted for each model using individual and combined datasets. The results include confidence contours at the levels $1σ$ and $2σ$. Our findings demonstrate that both parameterizations are consistent with observational data, with logarithmic parameterization showing slightly better constraints in terms of parameter evolution. Furthermore, we employed a statefinder diagnostic to analyze the geometric behavior of the models, providing an effective distinction between the two DE scenarios. This study contributes to a deeper understanding of DE evolution and its constraints in light of current cosmological data.

physics.gen-ph↗

arXiv2026

Dynamical Dark Energy Signatures from a New Transition $Om(z)$ Parametrization in Flat FLRW Cosmology

We investigate a cosmic scenario using a new transition parameterization of the $Om(z)$ diagnostic, $Om(z) = \frac{z^l}{(1+z)^m}$, in the spatially flat Friedmann Lemaître Robertson-Walker (FLRW) framework. Using observational datasets such as Observational Hubble Data (OHD), Pantheon Plus (PP), and SH0ES, we analyze the evolution of the $Om(z)$ function to probe deviations from the standard $Λ$CDM model and constrain free parameter space {$H_0$, l, m } using Markov Chain Monte Carlo (MCMC) analysis with the emcee sampler. Our analysis reveals a clear transition in the slope of $Om(z)$ from negative to positive at transition redshift values $z_t \approx 1.41$, $0.65$, and $0.33$ for the OHD, OHD+PP, and OHD+PP$\&$SH0ES datasets, respectively. This behavior suggests a dynamical evolution of dark energy, indicating a transition from a quintessence-like phase to a phantom regime. From the combined OHD+PP$\&$SH0ES dataset, we obtain a best-fit value of the Hubble constant $ H_0 = 73.01 \pm 0.36 \, \mathrm{km\,s^{-1}\,Mpc^{-1}} $, which is consistent with the SH0ES calibration and supports the viability of our model. Additionally, our analysis indicates that the current age of the Universe is approximately $13 \sim 14$ Gyr from all available combinations of datasets, which is consistent with observational expectations. Further, we find that the deceleration-to-acceleration transition, which marks the beginning of cosmic acceleration, is inferred to occur within the redshift interval $z_t \in [0.5, 0.8]$, highlighting the emergence of dark energy as the dominant component in the Universe's recent expansion history. Our transition $Om(z)$ parameterization captured progressive cosmological changes and enabled seamless interpolation over cosmic epochs.

gr-qc↗

arXiv2026

Dynamical Oscillations in Dark Energy: Joint Constraints on the $w_{sin}$CDM Model from DESI, OHD, and Supernova Samples

In this study, we investigate the oscillatory dark energy model $w_{\sin}\mathrm{CDM}$ based on the DESI BAO data together with OHD, Pantheon Plus, and SH0ES measurements. We examine how the DESI data influence the dark energy equation-of-state plane $(w_0, w_a)$ within cosmological models that are free from Hubble tension and employ a Monte Carlo Markov Chain (MCMC) approach. Our findings indicate that although the parameter space still favors $w_a < 0$ and $w_0 > -1$ , the cosmological constant remains consistent with the DESI+OHD+PP combination at the $2σ$ level. We also observe that the best-fit Hubble constant $H_0$ is higher for the DESI+OHD+PP+SH0ES data combination, leading to a residual Hubble tension of less than $1σ$ to remain consistent with the SH0ES measurement. These results suggest that attempts to address the Hubble tension tend to reduce indication of DESI for the oscillatory dark energy model. Therefore, claims that the cosmological constant should be approached with greater caution, considering both the latest observational datasets and the existing cosmological tensions. We also obtained the present deceleration parameter and the effective equation-of-state value as $q_0 = -0.36$ and $w_{\mathrm{eff}} = -0.57$, respectively, for the DESI+OHD+PP+SH0ES dataset combination. Further analysis indicated a strong departure of $w_0$ from $w=-1$ at the $4σ$ level for the DR2+OHD+DES-5yr data combination. The inferred $Ω_{m}$ tended to shift toward higher values when supernova samples were included, indicating a systematic preference for larger $Ω_{m}$ in combinations involving supernova data.

physics.gen-ph↗

arXiv2025

Constraints on Spatial Curvature and Dark Energy Dynamics in the $w$CDM Model from DESI DR1 and DR2

In this study, we investigate the $w$CDM dynamical dark energy model with spatial curvature utilizing the recently released DESI Collaboration data (DR1 and DR2) in conjunction with other observational probes such as BBN, Observational Hubble Data (OHD), and Pantheon Plus (PP). Our investigation attempts to discover which DESI dataset gives a better match to the $w$CDM framework and assess the impact of spatial curvature on cosmological constraints. We find that the cosmic curvature parameter, $Ω_k$, disfavors the cosmological constant for the DR2+BBN and DR2+BBN+OHD data combinations. However, the deviation from the cosmological constant remains below the $1σ$ level, indicating a mild preference for a open universe. In contrast, when using the DR1 based combinations namely DR1+BBN and DR1+BBN+OHD-the deviation from the cosmological constant increases to approximately $1.2σ$, suggesting a slightly stronger indication of a open geometry. Also, the best-fit values of the Hubble constant ($H_0$) obtained from the DR1+BBN+OHD+PP and DR2+BBN+OHD+PP combinations within the dynamical dark energy model are consistent with the results reported by the Planck Collaboration. Our findings provide constraints on the dark energy EoS parameter $ w_{\mathrm{}0}$, reveal a mild but notable deviation from the vacuum energy ($w = -1$) scenario at a significance level $1.8σ$ from DR2+BBN+OHD+PP and $0.5σ$ from DR1+BBN+OHD+PP, both favoring the quintessence region of dark energy. Furthermore, the key physical distance measures $D_H$, $D_V$, and $D_M$ show better consistency with our model when analyzed with the DR2 data.

astro-ph.CO↗

arXiv2025

Beyond $Λ$CDM: Exploring a Dynamical Cosmological Constant Framework Consistent with Late-Time Observations

In this work, we investigate a cosmological scenario with a time-dependent cosmological constant $Λ$(t) within the spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) framework. Here we study a power-law $Λ(t)$CDM model characterized by a dynamic cosmological constant expressed as a function of the Hubble parameter and its derivative $Λ(t)$ $=α(\dot H+H^{2})+λH^2+4πGρη.$ Using recent observational datasets (DESI BAO, OHD, and PP\&SH0ES), we constrain the model's free parameters $(H_{0},α,λ,η)$ and analyze their impact on key cosmological quantities. A Markov chain Monte Carlo (MCMC) analysis of the best-fit value of $H_{0}=71.9\pm 0.23$ km/s/Mpc from PP\&SH0ES analysis only, which substantially alleviates the existing tension between early and late-time determinations of the Hubble constant, reducing it to $\sim1.5σ$. The reconstructed $Om$ diagnostic exhibits a negative slope, indicating a dynamic dark energy behavior with quintessence-like characteristics ($ω>-1$). These results suggest that the proposed $Λ(t)$ model provides a viable alternative to the standard $Λ$CDM paradigm to explain the late-time acceleration of the universe. Our findings show that this model alleviates the Hubble tension more effectively than the standard $Λ$CDM . The model also demonstrates compatibility with late-time Hubble parameter observations and offers a compelling framework to address the limitations of $Λ$CDM.

gr-qc↗

arXiv2025

Investigating the $w$CDM Model with Latest DESI BAO Observations

In this study, we explore the impact of various combinations of CMB-independent datasets, including the recent DESI BAO measurements, on the equation of state (EoS) of dark energy and other cosmological parameters within the framework of the dynamical dark energy model ($w$CDM). Assuming a constant EoS parameter for dark energy, we derive constraints on the free parameters of the model using observational datasets such as DESI BAO, BBN, Observational Hubble Data (OHD), and Pantheon Plus (SN$^+$) $\&$ SH0ES. Our analysis examines the deviations of the $w$CDM model from the standard $Λ$CDM scenario and assesses its implications for cosmological tensions, particularly the $H_0$ tension [$\text{km} \text{s}^{-1} \text{Mpc}^{-1}$]. We find that the combination of DESI BAO + BBN + OHD + SN$^+$ (DESI BAO + BBN + OHD + SN$^+$ \&SH0ES) datasets provides constraints on $w_{\mathrm{de}0}$, suggesting a possible deviation from the cosmological constant scenario at a significance level of $1.6σ$ ($1.4σ$), respectively. Furthermore, we observe an inverse correlation between $w_{\text{de0}}$ and $H_0$, which highlights the role of dark energy dynamics in resolving the tension $H_0$ by approximately $2.1σ(0.8σ)$ from DESI BAO + BBN + OHD (DESI BAO + BBN + OHD + SN$^+$ \&SH0ES) datasets, respectively. Our findings offer valuable insights into the nature of dark energy and its influence on the cosmic expansion history, with implications for future observational efforts. We utilize the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) to evaluate our model's performance. The results indicate that the $w$CDM model demonstrates superior effectiveness.

astro-ph.CO↗

arXiv2025

Cosmological Implications of a New Creation Field in Hoyle-Narlikar Gravity with Bulk Viscous Fluid

In this study, we present a comprehensive investigation of the Narlikar gravity model with bulk viscous fluid by the new foam of creation field $C(t) = t + \int α(1 - a)dt + c_1$, based on the Hoyle-Narlikar's creation-field theory, using a joint analysis of Observational Hubble Data (OHD) and the Pantheon supernova (PP) compilation. Our analysis reveals that the creation field coupling constant $(f)$ is always positive within the Narlikar gravity model from OHD+PP data sets. The best-fit estimates yield $ H_0 = 71.2 \pm 2.1 \text{km s}^{-1}\text{Mpc}^{-1}$ and $ξ_0 = 0.23$, quoted at the $1 σ$ level. The Narlikar gravity model predicts a transition redshift of $z_t \approx 0.63$ marking the onset of late-time cosmic acceleration, with the corresponding age of the Universe estimated as $13.50\pm1.80 Gyr$. Interestingly, the inferred higher value of $H_0$, relative to SH0ES determinations, suggests a possible alleviation of the $\sim 4.1σ$ Hubble tension. Furthermore, we assess the stability of the model and demonstrate that the late-time acceleration can be consistently explained through the energy conditions. This model retains dynamical flexibility while ensuring analytical tractability and provides a promising framework to investigate the cosmological implications of Hoyle-Narlikar gravity, particularly regarding late-time acceleration and the evolution of dark energy.

gr-qc↗

arXiv2025

Testing $f(T)$ Gravity with Cosmological Observations: Confronting the Hubble Tension and Implications for the Late-Time Universe

In recent years, modifications to General Relativity (GR) have been explored to address cosmological observations, particularly in the context of late-time cosmic acceleration. Among these, modifications based on the Teleparallel Equivalent of General Relativity (TEGR), particularly $f(T)$ gravity, have gained significant attention. In this work, we investigate the scalar perturbations in $f(T)$ gravity, focusing on how these perturbations modify the Poisson and lensing equations and how they impact cosmological observables. By incorporating observational data from cosmic chromatometers, Big Bang nucleosynthesis, the DESI BAO survey, and Type Ia Supernovae (SNe Ia), we derive constraints on the parameters of the $f(T)$ power-law model. Our results suggest that $f(T)$ gravity can effectively alleviate some of the tensions observed in the standard $Λ$CDM model, including the Hubble constant ($H_0$) discrepancy. Furthermore, the evolution of the supernova luminosity and its dependence on the gravitational constant are considered to refine the measurement of cosmological parameters. The model's ability to address the $H_0$ tension is critically examined, and we find that $f(T)$ gravity offers a viable alternative to the standard model. The work concludes by comparing the fits of the $f(T)$ gravity model to the $Λ$CDM model using various information criteria, revealing key insights into the viability of modified gravity in contemporary cosmology.

astro-ph.CO↗