arXiv subjects

José Antonio Nájera

Publications and source records attributed to José Antonio Nájera.

8 recordsLinked to original sources

arXiv2026

Constraints on the gravitational potential from DESI DR2 BAO and its implications for the local void scenario

We constrain the difference in gravitational potential between our location and sources at $z \gtrsim 0.3$ using datasets at those redshifts. Our motivation is that the Hubble tension might be caused by a local void, as suggested by galaxy number counts. This would increase the redshift through outflow and gravitational redshift (GR). Only the latter is important at high redshift, where a void contributes a fixed additional GR contribution of $z_0$ due to our location on a potential hill. This $z_0$ model has various subtle effects that were not previously considered, including a hotter CMB and reduced BAO scale $r_{\rm d}$. We test whether $z_0$ can have the previously expected value of 0.84%, which was based on fitting void parameters to galaxy number counts and local $H_0$ measurements. Combining BBN, CMB, BAO, and CC datasets at $z > 0.5$, we find that $z_0 = -0.4^{+0.8}_{-0.9}\%$, which rises to $-0.1 \pm 0.7\%$ when extending our analysis down to $z > 0.29$. Although the results prefer the standard value of $z_0 = 0$, the best-fitting model with $z_0 = 0.84\%$ fits the data almost as well as $Λ$CDM, with $Δχ^2 < 2$. We find that $Λ$CDM faces a $3.07σ$ BAO anomaly in the standard $(H_0 r_{\rm d}, Ω_{\rm m})$ parameter space, where different regions are preferred by BAO and non-BAO datasets from $z > 0.29$. Fixing $z_0 = 0.84\%$ reduces this to $2.79σ$. This suggests that a local void large enough to solve the Hubble tension cannot be ruled out by higher-redshift datasets despite its novel impacts on them.

astro-ph.CO↗

arXiv2026

The subtle statistics of the distance ladder: On the distance prior and selection effects

Statistical methodology is rarely considered significant in distance-ladder studies or a potential contributor to the Hubble tension. We suggest it should be, highlighting two appreciable issues. First, astronomical distances are inferred latent parameters, requiring a prior. We show that the (often implicit) uniform priors on distance moduli common to Bayesian distance-ladder analyses bias distances low due to objects being uniformly distributed in volume, which biases the Hubble constant high. Frequentist $χ^2$ methods are unbiased for volume- or redshift-limited samples only if the redshift uncertainty (including peculiar velocities) vanishes, though simulation-based calibration can correct the bias. Second, in a Bayesian framework, selection effects introduce additional posterior factors describing the probability of objects entering the sample under the model. These partly counteract the volume prior, depending on the nature of the selection. After detailed analytic and mock-based studies, we quantify the volume-prior effect in the CosmicFlows-4 and SH0ES samples. Both use frequentist methods, so the effect appears as a potential estimator bias rather than a missing prior. The implied Hubble constant shifts are significant but must not be applied na\"ıvely -- principled selection modelling is also required, as we investigate explicitly for CosmicFlows-4. Both effects should already be captured by the SH0ES pipeline's simulation-based bias corrections. Our work highlights the crucial need to model both distances and selection accurately, either directly in a Bayesian forward model, or via post-hoc simulation-based corrections with realistic source and selection distributions. Such modelling requires samples with known, homogeneous selection criteria, which future surveys should prioritise.

astro-ph.CO↗

arXiv2026

Comparing measures of the Hubble and BAO tensions in $Λ$CDM and possible solutions in $f(Q)$ gravity

We test whether $f(Q)$ symmetric teleparallel gravity theories can solve the Hubble tension consistently with DESI DR2 BAO. We consider three $f(Q)$ functional forms: logarithmic, exponential, and hyperbolic tangent. We extend these models by allowing a cosmological constant, and compare to phenomenological models with a flexible exponential, hyperbolic secant, and polynomial decay addition to the standard $Λ$CDM $H(z)$. We test these models against DESI DR2 BAO, CMB ($Planck$ 2018 + SPT-3G + ACT DR6), local $H_0$, and Cosmic Chronometer data. The logarithmic and hyperbolic tangent $f(Q)$ models do not provide an adequate solution, but the exponential model does. Furthermore, it slightly reduces the $(Ω_m, H_0 r_d)$ parameter space tension between CMB and BAO datasets to $2.56σ$, down from $2.65σ$ for $Λ$CDM. Although $Λ$CDM faces only $1.66σ$ tension in DESI data space, the $1σ$ higher tension in parameter space suggests a real anomaly. The models assisted by the cosmological constant perform slightly better still, at the cost of undermined theoretical motivation. They also perform poorly once local $H_0$ measurements are included. The phenomenological models fit all data reasonably well, yet the best-fitting models predict isotropically averaged BAO distances exceeding the DESI DR2 measurements at all redshifts. This highlights the difficulties of finding a theoretically motivated solution to the Hubble tension while remaining consistent with BAO data.

astro-ph.CO↗

arXiv2025

Consistencies and inconsistencies in redshift-independent distances

Redshift-independent distances underpin much of astrophysics, and there exists a plethora of methods to estimate them. However, the extent to which the distances they imply are consistent, while crucial for the integrity of the distance ladder, has been little explored. We construct a statistical framework to assess both internal (between measurements with the same method) and external (between-method) consistency by comparing differences between distances to their quoted statistical uncertainties in the NASA/IPAC Extragalactic Database of Distances (NED-D). 66 of the 76 indicators in NED-D are amenable to a consistency test by having at least two measurements to the same galaxy or at least one measurement to a galaxy also measured by another method. We find that only 12 of these methods produce self-consistent distances across literature determinations, of which 7 are also consistent with distances to the same galaxies measured by all other methods. The most consistent 6 methods (M-stars luminosity, Novae, Masers, Globular Cluster Fundamental Plane, O- and B-type Supergiants and BL Lac Luminosity) also give similar average distances to the mean of all indicators, while the 7th (Proper Motion) underestimates distances relative to the mean by 17.1%. We also investigate consistency of Cepheid distances in the SH0ES 2022 catalogue, finding no evidence for unaccounted-for systematics. Our NED-D results imply that considerable work remains to obtain reliable distances by a multitude of methods, a crucial endeavour for constructing a multiply cross-checked and fully robust distance ladder. We make our code publicly available.

astro-ph.CO↗

arXiv2024

Phantom scalar field cosmologies constrained by early cosmic measurements

In this work, we explore new constraints on phantom scalar field cosmologies with a scalar field employing early times catalogues related to CMB measurements, along with the local standard observables, like Supernovae Type Ia (SNIa), $H(z)$ measurements (Cosmic Clocks), and Baryon Acoustic Oscillations (BAO) baselines. In particular, we studied a tracker phantom field with hyperbolic polar coordinates that have been proposed in the literature. The main goal is to obtain precise cosmological constraints for $H_0$ and $σ_8$, in comparison to other constructions that present tension in early cosmological parameters. Our results show that phantom scalar field cosmologies have a reduced statistical tension on $H_0$ that it is less than 3$σ$ using model-independent CMB catalogues as SPT-3G+WMAP9 and ACTPol DR-4+WMAP9 baselines. This suggests these models using a different phantom potential might address the Hubble constant problem and reduce the systematics involved.

gr-qc↗

arXiv2023

Constraints on $f(Q)$ logarithmic model using gravitational wave standard sirens

In this paper, we study the constraints on the $f(Q)=Q/(8πG) - α\ln(Q/Q_0)$, symmetric teleparallel model using local measurements and gravitational wave mock standard sirens. Using observational local SNIa and BAO data and energy conditions, the logarithmic $f(Q)$ model is capable of explaining the cosmic late-time acceleration by geometrical means. This result suggests that the logarithmic symmetric teleparallel model could be a candidate to solve the cosmological constant problem. In the case of the simulated standard siren data, by using the performance of the future ET and LISA detectors, we expect to be able to measure the current Hubble constant $H_0$, and the matter content $Ω_m$, with a precision better than 1\% and 6\%, respectively. Furthermore, we explore the predicted $f(Q)$ logarithmic model deviation from the standard GR using ET and LISA mock standard sirens. The ratio $d_L^{\text{gw}}(z)/d_L^{\text{em}}(z)$, which quantifies the deviation from GR gives us a significant deviation higher than 13\% at $z=1$, and it continues growing to reach a deviation higher than 18\% in its median value. Future standard siren data will be able to quantify the strength of the deviation from GR and hence whether a cosmology like the one implied by this $f(Q)$ model is feasible.

gr-qc↗

arXiv2023

Comment on: "Questioning the $H_0$ tension via the look-back time"

Recently, it has been proposed that Hubble tension can be addressed in the $Λ$CDM model if the lookback time approach is considered on the redshift $z$ measured. From this interesting proposal, the lookback time evolution seems to match the observational values of the current Hubble parameter $H_0$ at any $z$. In this comment, we discuss that using a lookback time approach function $H_{0}^{(z)}$, does not address the $H_0$ tension issue completely. It has been studied that the growing tension among early-time and local measurements of $H_0$ are possible concealed sources of systematic error in observations or modifications (or extensions) to the standard $Λ$CDM model. Furthermore, we show that the age of the Universe is sensitive to both $Ω_m$ and $H_0$ in flat $Λ$CDM-like cosmological models.

gr-qc↗

arXiv2022

Effects of the matter Lagrangian degeneracy in $f(Q,T)$ gravity

In this paper, we investigated the theoretical and cosmological effects of the matter Lagrangian degeneracy in an extension of the Symmetric Teleparallel Equivalent of General Relativity, denoted as $f (Q, T )$ gravity. This degeneracy comes from the fact that both $\mathcal{L}_m = p$ and $\mathcal{L}_m = -ρ$ can give rise to the stress-energy tensor of a perfect fluid. The $f(Q,T)$ equations depend on the form of the matter Lagrangian and hence they also have a degeneracy that has influence on the density evolution of dust matter and radiation, on the form of the generalized Friedmann equations and also shows changes in the cosmological parameters confidence regions when performing Monte Carlo Markov Chains analyses. Our results suggest that since changing the matter Lagrangian causes different theoretical and cosmological results, future studies in $f(Q,T)$ gravity should consider both forms of the matter Lagrangians to account for the different mathematical and observational results.

gr-qc↗