arXiv subjects

Himanshu Chaudhary

Publications and source records attributed to Himanshu Chaudhary.

At least 19 recordsLinked to original sources

arXiv2026

Finding black hole spins efficiently during a numerical binary evolution

The dynamics of a binary black hole system depend on its masses and spins. For a binary at finite separation, it is not possible to define these quantities in an unambiguous way; however, there are several reasonable definitions that reduce to the expected values in the limit of infinite separation. Approximate Killing vector (AKV) spin is one of the spin definitions used in the numerical relativity code SpEC. AKV spin requires finding approximate Killing vectors on an apparent horizon, which reduces to a generalized eigenvalue problem of size $\mathcal{O}(L^2)$, and a direct solve has time complexity $\mathcal{O}(L^6)$, where $L$ is the highest spherical harmonic mode used to represent the apparent horizon. This scaling means that the cost of computing AKV spins increases rapidly as we simulate systems at higher resolutions, especially those with high spin or mass ratios. We describe a new algorithm for computing AKV spins that is much faster than the current algorithm.

gr-qc↗

arXiv2026

Constraints on the Modified Emergent Dark Energy Model Using DESI DR2 BAO

In this work, we investigate the modified emergent dark energy (MEDE) model using baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2), together with CMB information from the {\tt LoLLiPoP} (low-$\ell$) and {\tt HiLLiPoP} (high-$\ell$) likelihoods based on the latest Planck NPIPE PR4 release, Planck PR4 lensing, ACT DR6 lensing, and three Type Ia supernova samples (Pantheon$+$, DES-Dovekie, and Union3). We find that the MEDE model remains largely consistent with the standard $Λ$CDM cosmology. Although small departures from $Λ$CDM are allowed, the inclusion of SNe~Ia data drives the model parameters toward the standard cosmological scenario, with the parameter $α$ remaining consistent with $α=0$ at the $1σ$ level. The model does not significantly alleviate the $H_0$ or $S_8$ tensions: the inferred $H_0$ values remain below the SH0ES measurement, the sound horizon $r_d$ is nearly unchanged, and the predicted $S_8$ values remain close to those of $Λ$CDM. The reconstructed cosmological evolution closely follows the $Λ$CDM prediction, with deviations generally below the $0.5σ$ level. While the CMB + DESI DR2 dataset favors a full phantom regime, the inclusion of SNe~Ia shifts the evolution toward a full quintessence regime. Finally, although the $Δχ^2_{\rm MAP}$ and $Δ{\rm AIC}$ criteria indicate a marginally better fit than $Λ$CDM, the logarithmic Bayes factor provides only inconclusive evidence in favor of the MEDE model. Overall, the MEDE model remains compatible with current observations but does not exhibit the phantom-crossing behavior suggested by recent DESI DR2 analyses.

physics.gen-ph↗

arXiv2026

Conformal Killing Gravity: New Constraints from DESI DR2 BAO datasets

We investigate a geometric approach referred to as the Conformal Killing Gravity (CKG), in which the dark energy sector emerges naturally from the conformal Killing symmetry of the Robertson--Walker space-time. Within this framework, the divergence-free conformal Killing tensor behaves as an effective perfect fluid, giving rise to a dynamical dark-energy component whose density, pressure, and equation of state are uniquely determined by the underlying geometry, without introducing any empirical dark-energy parametrization. The resulting CKG model extends the standard $Λ$CDM cosmology through a single additional parameter while recovering the $Λ$CDM limit in the absence of the geometric contribution. We constrain the model using Planck PR4 (NPIPE) CMB temperature, polarization, and lensing observations, ACT DR6 CMB lensing, DESI DR2 baryon acoustic oscillation measurements, and the Pantheon$+$, DES-Dovekie, and Union3 Type Ia supernova compilations. The analysis shows that the CKG favors a quintessence-like dark-energy evolution with no evidence for phantom crossing, while the reconstructed equation of state rapidly approaches the cosmological constant at earlier cosmic times. Furthermore, the model predicts a future critical redshift in the range $-0.8 \lesssim z_c \lesssim -0.7$, indicating that the present cosmic expansion eventually reaches a turning point before the formal singular limit at $z=-1$. Since the geometric contribution modifies only the post-recombination expansion history, the sound horizon remains essentially unchanged and the model does not provide a complete solution to the $H_0$ tension. Our results demonstrate that the CKG provides a simple, physically motivated, and observationally favored framework for describing the late-time accelerated expansion of the Universe.

astro-ph.CO↗

arXiv2026

No preference for generalized emergent dark energy from current cosmological data

In this work, we revisit the generalized emergent dark energy model by confronting it with DESI DR2 baryon acoustic oscillation measurements, in combination with joint CMB data from ACT, SPT, and Planck, as well as Type Ia supernova samples including Pantheon$^+$, DES-Dovekie, and Union3. We find that the GEDE model remains compatible with the $Λ$CDM paradigm, with no statistically significant preference for deviations when all datasets are combined. In particular, the key model parameter $Δ$ is consistent with the $Λ$CDM value $Δ= 0$ within $2σ$ once SNe Ia data are included. Despite this overall agreement, the GEDE model does not exhibit the phantom crossing suggested by DESI DR2. Instead, the evolution of the dark energy equation of state $w(z)$ indicates that the model behaves either as a full phantom ($w < -1$) or quintessence ($w > -1$), depending on the dataset combination, without a clear transition across $w = -1$. When Pantheon$^+$ data are included, the model converges closely to $Λ$CDM with $w \simeq -1$. The GEDE model does not alleviate the existing cosmological tensions. The inferred values of $H_0$ remain in the range $67.9$-$69.8\ \mathrm{km,s^{-1},Mpc^{-1}}$, while the sound horizon $r_d$ and clustering parameter $S_8$ remain consistent with $Λ$CDM, failing to resolve the $H_0$ and $S_8$ tensions. Finally, both Gaussian significance levels ($<2σ$) and Bayesian evidence ($\ln B_{i,j} < 1$) indicate no statistically significant preference for GEDE over $Λ$CDM. We conclude that, although DESI DR2 hints at dynamical dark energy, the GEDE model remains observationally indistinguishable from $Λ$CDM and does not support the Quintom-B-type behavior suggested by DESI DR2.

astro-ph.CO↗

arXiv2026

Testing the Anton-Schmidt dark energy model with the DESI DR2 measurements

We present a comparative cosmological analysis of the Anton-Schmidt, $Λ$CDM, and CPL models using baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Data Release 2, combined with the Planck PR4 (NPIPE) CamSpec Cosmic Microwave Background likelihoods and three Type Ia supernova catalogues: Pantheon$+$, DES-Dovekie, and Union3. We use Markov Chain Monte Carlo analyses to constrain the parameters of the Anton-Schmidt model against each dataset combination. We find that the Anton-Schmidt model provides a good fit to current cosmological observations. The Anton-Schmidt model provides a good fit to the current cosmological observations but does not provide a significant alleviation of either the $H_0$ or the $S_8$ tensions. The Anton-Schmidt parameter is tightly constrained to $B \simeq -0.38$, indicating that the logarithmic correction becomes relevant only at late times. The Anton-Schmidt and CPL models predict quintessence-like present-day dark-energy equations of state and shows Quintom-B evolution, with their dark-energy equation-of-state parameters crossing the phantom divide at approximately $z \approx 0.5$. The characteristic density scale is constrained to be $ρ_\ast/ρ_{c,0}\sim4\text{--}5$, substantially smaller than the large density scales typically assumed in logotropic-inspired scenarios, indicating that the Anton-Schmidt correction mainly affects the late-time expansion history. Finally, Bayesian evidence shows moderate-to-strong preference for the Anton-Schmidt model over the $Λ$CDM model and strong-to-decisive preference over the CPL parametrization. Although the Anton-Schmidt model does not alleviate the current cosmological tensions, it emerges as a statistically favored dynamical dark-energy scenario whose cosmological implications deserve further tested with forthcoming Stage-IV large-scale structure observations.

physics.gen-ph↗

arXiv2026

Equatorial Periodic Orbits and Gravitational Wave Phenomenology around Spherically-symmetric vacuum solution in Freund-Nambu scalar-tensor gravity

We investigate test particle dynamics and gravitational wave (GW) phenomenology in an exact spherically symmetric vacuum solution of Freund - Nambu scalar - tensor gravity. This framework generalizes the Janis - Newman - Winicour (JNW) naked singularity via a geometric non - linear coupling $q$ and a direct scalar - particle coupling $g_s$. We demonstrate that these parameters systematically modify the Innermost Stable Circular Orbit (ISCO) - which shifts inward for $g_s > 0$ - and the Marginally Bound Orbit (MBO). Furthermore, we classify bound periodic trajectories to isolate extreme zoom - whirl orbits exhibiting intense periapsis precession. By applying the Numerical Kludge method to Extreme Mass - Ratio Inspirals (EMRIs), we reveal that scalar - tensor corrections induce a macroscopic temporal dephasing in high - frequency GW bursts, even when the orbit's spatial topology is preserved. These unique phase shifts offer a robust diagnostic signature for future space-based observatories like LISA to probe the strong - field regime and constrain scalar - tensor extensions of general relativity.

gr-qc↗

arXiv2026

Evidence of dynamical dark energy found via the DESI DR2 Lyman$α$ forest

We present a comprehensive analysis of the cosmological implications of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) Lyman-$α$ forest baryon acoustic oscillation (BAO) measurements, combined with DESI DR2 galaxy BAO, Type Ia supernova samples (Pantheon$^+$, DES-Dovekie, and Union3), and the cosmic microwave background CamSpec likelihood. We consider several dark-energy parameterizations, including Chevallier-Polarski-Linder, logarithmic, exponential, Jassal-Bagla-Padmanabhan, Barboza-Alcaniz, and generalized emergent dark energy, as well as the $w$CDM model and non-flat extensions of $Λ$CDM and $w$CDM. Using the Metropolis-Hastings MCMC algorithm, we constrain cosmological parameters and compute Bayesian evidence with \texttt{MCEvidence}. We find that non-flat extensions remain consistent with spatial flatness, with $Ω_k \approx 0$. All parameterizations favor a dynamical dark-energy scenario with $w_0 > -1$, $w_a < 0$, and $w_0 + w_a < -1$, consistent with a Quintom-B behavior. A moderate preference for dynamical dark-energy models is found relative to $Λ$CDM, reaching up to $\sim3.10σ$ for Ly$α$ + CMB + galaxy BAO. When combined with SNe~Ia datasets, the deviations decrease to $\lesssim2σ$, corresponding to inconclusive preference. The Bayes factor ($\ln B_{ij}$) shows that model preference depends strongly on the dataset combination: $w$CDM and o$w$CDM exhibit moderate evidence for Ly$α$ + CMB + galaxy BAO, while most other models show weak or inconclusive evidence. With Pantheon$^{+}$ or DES-Dovekie, o$w$CDM shows strong evidence, whereas other models remain moderately favored.

astro-ph.CO↗

arXiv2026

Cosmological Tests of $f(R,G,T)$ Dark Energy Model in FRW Universe

This research article presents a new cosmological model formulated within the $f(R,G,T)$ framework, focusing on the observational signatures and parameter constraints of the model. The Markov Chain Monte Carlo (MCMC) technique is employed to effectively explore the parameter space using data from 36 Cosmic Chronometers and 1701 Pantheon Plus data points. A comparative analysis is conducted between the proposed $f(R,G,T)$ model and the widely accepted $Λ$CDM model, considering various cosmological parameters, such as Deceleration, Snap, and Jerk. By evaluating these parameters, valuable insights into the dynamics and evolution of the universe within the context of the new model are obtained. Diagnostic tests including Statefinder and Om Diagnostic are performed to further investigate the behavior and consistency of the $f(R,G,T)$ model. These tests provide deeper insights into the properties of the model and its compatibility with observational data. The model is subjected to statistical analysis using Information Criteria to rigorously assess its goodness of fit to the data. This analysis helps determine the level of agreement between the $f(R,G,T)$ model and the observational data, establishing the viability and reliability of the proposed cosmological framework. The results highlight the potential of the $f(R,G,T)$ framework in understanding the fundamental aspects of the universe's evolution and dynamics. The comparative analysis with the $Λ$CDM model, along with the comprehensive diagnostic tests performed, demonstrates the efficacy and validity of the $f(R,G,T)$ model in explaining observed cosmological phenomena. These findings contribute to the ongoing pursuit of accurate and comprehensive models that provide a deeper understanding of the nature of our universe.

gr-qc↗

arXiv2026

Evidence for evolving dark energy from DESI DR2 BAO and Pantheon$^+$, DES-Dovekie, and Union3

Evidences for evolving dark energy are shown using baryon acoustic oscillation measurements from the recent Dark Energy Spectroscopic Instrument Data Release 2 , combined with different Type Ia supernova datasets (Pantheon$^+$, DES-Dovekie, and Union3) and the CMB compressed likelihood. We examine several dark energy parameterizations, including the Logarithmic, Exponential, CPL, BA, JBP, Thawing, Mirage, and GEDE models. Analyzing the DESI DR2 measurements alone, we find that evidence for evolving dark energy is primarily driven by the LRG1-2 tracers, as their inclusion yields a preferred value of $w_0 > -1$. However, as each tracer provides only limited observables, this preference can result in an underconstrained and potentially unstable inference. Further, we find that each dark energy model predicts values in the $w_0 > -1$, $w_a < 0$ quadrant, a region characterized by the Quintom-B type dark energy scenario. The logarithmic bayes factor shows that, among all models, the Mirage model shows the inconclusive-to-moderate evidence across all dataset combinations. Consistently, the statistical significance remains modest, with $Nσ\sim 1.1$-$2.3$, and no model showing a robust preference for dynamical dark energy using late-time datasets alone. The evolution of $w(z)$ shows a phantom crossing around $z \sim 0.5$ in most dynamical dark energy models, and the evolution of $f_{\mathrm{DE}}(z)$ converges to $f_{\mathrm{DE}}(0) = 1$ in all dark energy models.

astro-ph.CO↗

arXiv2026

Probing departures from $Λ$CDM by late-time datasets

Observational data play a pivotal role in identifying cosmological models that are both theoretically consistent and empirically viable. In this work, we investigate the level of preference for dynamical dark energy over a cosmological constant using current late-time observational datasets, including Cosmic Chronometers , Baryon Acoustic Oscillations from DESI DR2, and different Type Ia supernova catalogs (Pantheon$^+$, DES-Dovekie, Union3). We analyze various dynamical dark energy models, including $ω$CDM, o$ω$CDM, $ω_0ω_a$CDM, Logarithmic, Exponential, JBP, BA, and GEDE. In most cases, the o$Λ$CDM and o$ω$CDM models favor an open Universe. For the o$ω$CDM, the inclusion of DES-Dovekie or Union3 data together with CC and DESI DR2 favors a nearly flat geometry. Using the CC + DESI DR2 dataset, the preference for dynamical dark energy lies between the $1$-$2σ$ level. When different supernova catalogs (DES-Dovekie or Union3) are included, the deviation from $Λ$CDM in the $ω$CDM, $ω_0ω_a$CDM, Logarithmic, JBP, BA, and GEDE models increases to the $2$-$2.74σ$ level, while the Pantheon$^{+}$ sample yields deviations below the $2σ$ level. We find consistent evidence for $ω_0 > -1$ and $ω_a < 0$ across all dark energy models, indicating a preference for dynamical dark energy characterized by a Quintom-B type scenario. The $Λ$CDM paradigm has long served as the standard framework of modern cosmology; however recent DESI DR2 results have exposed emerging tensions with the cosmological constant $Λ$, hinting at possible new physics in the dark energy sector. Even so, the currently available data are still not strong enough to definitively rule out the $Λ$CDM model.

astro-ph.CO↗

arXiv2026

$Λ(t)$CDM Model: Cosmological Implications and Dynamical System Analysis

We investigated a time-varying cosmological constant model using recent BAO measurements from DESI DR2, combined with Type Ia supernova samples (Pantheon$^{+}$, DES-Dovekie, and Union3) and CMB shift parameters, to constrain the $Λ(t)$CDM model parameters via Markov Chain Monte Carlo analysis. We find that the interaction term $Q(z)$ shows a sign change for all dataset combinations by crossing $Q(z)=0$, depending on the choice of the dataset: at low redshift $Q(z)<0$, indicating vacuum energy decaying into dark matter, while at high redshift $Q(z)>0$, corresponding to dark matter decaying into vacuum energy. The dynamical system analysis found three critical points, namely $P_1,P_2$, and $P_3$ respectively. The resulting critical points, determined by the underlying cosmological parameters, correspond to distinct epochs in cosmic evolution. Depending on the parameter combinations, these points characterize various cosmological phases, ranging from an accelerated stiff matter-dominated era to late-time accelerated expansion. The stability of each critical point is analyzed using linear stability theory, with the relevant physical constraints on the cosmological parameters duly incorporated throughout the analysis. For each dataset combinations, the $Λ(t)$CDM model predicts that $ω_0 > -1$, showing a preference for dynamical dark energy over the cosmological constant scenario with $ω_0 = -1$. Consequently, the model exhibits a transition phase in the range $N \equiv \log a(t) \approx -0.51$ to $-0.48$ and predicts $q_0$ in the range $-0.54$ to $-0.52$, with the precise transition point depending on the choice of dataset. Finally, the Bayesian evidence shows strong support for the $Λ(t)$CDM model over $Λ$CDM

gr-qc↗

arXiv2025

Relativistic accretion process onto rotating black holes in Einstein-Euler-Heisenberg nonlinear electrodynamic gravity

In this study, we uncover the accretion dynamics and oscillatory behavior around rotating black holes within the EEH nonlinear electrodynamic framework by analyzing both the motion of test particles and numerically solving the general relativistic hydrodynamic equations. Using EEH geometry, we compute the structure of circular motion, the effective potential and force, and we evaluate the orbital, radial, and vertical epicyclic frequencies together with the Lense-Thirring and periastron precession rates. Our calculations show that, compared to the Kerr model, the charge parameter $Q$ and the spin parameter $a$ significantly modify the strong gravitational field and shift the characteristic frequencies. We then model the dynamical structure formed by matter accreting toward the EEH black hole through the BHL mechanism, finding that the parameter $Q$ increases the amount of infalling matter and strengthens shock-cone instabilities near the horizon, while farther from the black hole it suppresses accretion and reduces turbulence. Time-series analysis of the accretion rate reveals robust QPOs, whose low-frequency components arise from the precession of the shock cone, while high-frequency components appear as a consequence of strong-field instabilities modified by $Q$ and $a$. A systematic parameter-space exploration identifies the regions where EEH corrections maximize QPO activity, indicating that nonlinear electrodynamics can leave observable imprints on accretion flows and may be testable with QPO and horizon-scale observations.

gr-qc↗

arXiv2025

Is Dark Energy Dynamical in the DESI Era? A Critical Review

We investigate whether the recent DESI DR2 measurements provide or not evidences for dynamical dark energy by exploring the $ω_0ω_a$CDM model and its extensions with free $\sum m_ν$ and $N_{\mathrm{eff}}$. Using a comprehensive MCMC analysis with a wide range of cosmological datasets including DESI~DR2 BAO and Ly$α$ data, CMB compressed likelihoods, BBN, cosmic chronometers, and multiple Type~Ia supernova compilations, we assess the statistical preference for departures from $Λ$CDM.

astro-ph.CO↗

arXiv2025

Probing Generalized Emergent Dark Energy with DESI DR2

As an update on the initial findings of DESI, the new results provide the first hint of potential deviations from a cosmological constant ($ω=-1$), which, if confirmed with significance $>(2-4)σ$, would challenge the validity of $Λ$ within the $Λ$CDM model. We explore the Generalized Emergent Dark Energy (GEDE) model using recent BAO measurements from DESI DR2, Type Ia supernova compilations, and CMB distance priors. Employing nested sampling, we constrain the parameter $Δ$, which characterizes deviations from $Λ$CDM. Our analysis shows that with CMB+DESI DR2 alone, GEDE tends to prefer positive values of $Δ$. However, when different SNe Ia calibrations are included, the model favors negative values of $Δ$, corresponding to an earlier injection of dark energy. The Marginalized constraints on $ω(z)$ further shows that GEDE sharply emerges but then asymptotes to $ω=-1$ without crossing it. At $z \sim 1$ data, GEDE provides a better fit than $Λ$CDM, while at $z \lesssim 0.5$ the data favor $ω> -1$, bringing the model deviate from $Λ$CDM. Bayesian model comparison shows weak support for GEDE with CMB+DESI DR2 ($\ln BF=1.96$), moderate with PP ($\ln BF=2.65$), weak-to-moderate with Union3 ($\ln BF=2.34$), and weak with DES-SN5Y ($\ln BF=1.44$). Overall, GEDE is consistent with current data and mildly favored when SNe Ia are included, making it a viable extension of $Λ$CDM that merits further investigation with future high precision measurements.

astro-ph.CO↗

arXiv2025

Compact Objects in 4D Einstein Gauss Bonnet Gravity A Data Based Perspective

Cosmic evolution is the most sensational topic among researchers of modern cosmology. This article explores cosmic evolution in 4D Einstein Gauss Bonnet gravity, focusing on mass accretion of compact objects (black holes and wormholes) by dark energy. Three DE models CPL, JBP, and BA parameterizations are studied within 4D EGB gravity, with their Hubble parameters derived and compared against observational data (Cosmic Chronometers, Type Ia Supernovae, and Baryon Acoustic Oscillations). Bayesian analysis favors the CPL and BA models, with CPL providing the best fit. For black holes, mass accretion of CPL and JBP DE shows transitions between quintessence and phantom eras, while BA and $Λ$CDM strictly exhibit quintessence-like behavior, driving cosmic acceleration. In contrast, wormholes exhibit the opposite trend, favoring a phantom-dominated era for the BA and $Λ$CDM models. The study highlights the dynamic nature of DE in 4D EGB gravity and its role in cosmic expansion.

gr-qc↗

arXiv2025

Schrödinger-type $f(Q,T)$ gravity-nonmetricity driven cosmological evolution from inflation to the late Universe

We consider an $f(Q, T)$ gravity theory with a Schrödinger type vectorial non-metricity. In the presence of such a non-metricity, the length of vectors is preserved under autoparallel transport. We obtain the field equations assuming a vanishing total scalar curvature, implemented by a Lagrange multiplier, and investigate their cosmological implications. To do this, we derive the generalized Friedmann equations which now have terms involving the non-metricity and the Lagrange multiplier. Then, we consider two distinct cosmological applications of the model. First of all, by adopting distinct forms of these two basic variables and investigate the possibility of the existence of warm inflationary scenarios within the framework of these models. In particular, we consider the case that the non-metricity is described by a constant vector, and we show that with this assumption we recover standard general relativity. The scenario in which the Lagrange multiplier is a constant is also investigated, and we show that radiation can be created during the very early phases of expansion. The amount of radiation peaks at a certain time after which, there is a transition from an accelerating inflationary phase to a decelerating one. Moreover, we perform a detailed comparison of the predictions of the considered Schrödinger type cosmology with a set of observational data for the Hubble function, including Cosmic Chronometers, Type Ia Supernovae, and Baryon Acoustic Oscillations, using a Markov Chain Monte Carlo (MCMC) analysis, by adopting a simple linear form for the Lagrange density. The model predictions are also compared with the results of the $Λ$CDM standard paradigm. Our results indicate that the Schrödinger $f(Q,T)$ type theory can give a good description of the observational data for both the very early and the late Universe.

gr-qc↗

arXiv2025

Is the $Λ$CDM Model in Crisis?

We present strong evidence for dynamical dark energy that challenges the standard $Λ$CDM model. Several dark energy scenarios are explored, including $ω_0ω_a$CDM, logarithmic, exponential, JBP, and BA parameterizations, along with non-flat cosmologies allowing for spatial curvature ($Ω_k \neq 0$). Our analysis supports a flat Universe with $Ω_k \approx 0$. Using MCMC techniques, we constrain these models with observational data from DESI~DR2 baryon acoustic oscillations, Type~Ia supernovae, and compressed CMB likelihoods. The results provide strong statistical evidence that $ω\neq -1$, favoring dynamical dark-energy behavior consistent with a Quintom-B scenario ($ω_0 > -1$, $ω_a < 0$, and $ω_0 + ω_a < -1$). We also derive upper bounds on the total neutrino mass, $\sum m_ν$, using CMB + DESI~DR2 data: $\sum m_ν< 0.066~\mathrm{eV}$ for $Λ$CDM and $\sum m_ν< 0.075~\mathrm{eV}$ for $ω$CDM. In the non-flat extensions, o$Λ$CDM and o$ω$CDM, the limits relax to $\sum m_ν< 0.263~\mathrm{eV}$ and $\sum m_ν< 0.520~\mathrm{eV}$, respectively. For the other models $ω_0ω_a$CDM, logarithmic, exponential, JBP, BA, and GEDE the constraints range between $<0.043$ and $<0.127~\mathrm{eV}$. The effective number of relativistic species remains consistent with the standard value, $N_{\mathrm{eff}} = 3.044$, across all models. Bayesian evidence further shows that combining DES-SN5Y or Union3 supernova samples with CMB + DESI~DR2 produces measurable deviations from $Λ$CDM. Although no model reaches the $5σ$ significance threshold, several exhibit tensions exceeding $3σ$, suggesting emerging cracks in the cosmological constant paradigm.

gr-qc↗

arXiv2025

Observational tests of the conformal osculating Barthel-Kropina cosmological model

We consider detailed cosmological tests of dark energy models obtained from the general conformal transformation of the Kropina metric, representing an $(α,β)$-type Finslerian geometry. In particular, we restrict our analysis to the osculating Barthel Kropina geometry. The Kropina metric function is defined as the ratio of the square of a Riemannian metric $α$ and of the one-form $β$. In this framework, we also consider the role of the conformal transformations of the metric, which allows us to introduce a family of conformal Barthel-Kropina theories in an osculating geometry. The models obtained in this way are described by second-order field equations, in the presence of an effective scalar field induced by the conformal factor. The generalized Friedmann equations of the model are obtained by adopting for the Riemannian metric $α$ the Friedmann Lemaitre Robertson Walker representation. In order to close the cosmological field equations, we assume a specific relationship between the component of the one-form $β$ and the conformal factor. With this assumption, the cosmological evolution is determined by the initial conditions of the scalar field and a single free parameter $γ$ of the model. The conformal Barthel Kropina cosmological models are compared against several observational datasets, including Cosmic Chronometers, Type Ia Supernovae, and Baryon Acoustic Oscillations, using a Markov Chain Monte Carlo (MCMC) analysis, which allows the determination of $γ$. A comparison with the predictions of standard $Λ$CDM model is also performed. {Our results indicate that the conformal osculating Barthel Kropina model can be considered as a successful, and simple, alternative to standard cosmological models.

gr-qc↗