arXiv subjects

Miguel A. Sabogal

Publications and source records attributed to Miguel A. Sabogal.

14 recordsLinked to original sources

arXiv2026

Cosmological anatomy of interacting dark energy

Interacting dark energy (IDE) models, featuring interactions between dark matter (DM) and dark energy (DE), have received significant renewed interest. However, little attention has been devoted to understanding their genuine cosmological signatures, with comparisons against $Λ$CDM often carried out at fixed cosmological parameters. Considering the widely studied model with energy exchange rate proportional to the DE density, we carry out a three-level sequence of comparisons, starting from the naïve fixed-parameter comparison, then compensating for shifts in $θ_s$ and $z_{\text{eq}}$, and then removing effects due to the modified background. We show that fixing $θ_s$ and $z_{\text{eq}}$ leads to pre-recombination evolutions of the Weyl potential, photon monopole, and baryon velocity which are nearly identical to their $Λ$CDM counterparts, and hence virtually indistinguishable Cosmic Microwave Background (CMB) temperature power spectra. Comparing IDE to a non-interacting $w$CDM model with the same background, we find small scale-dependent signatures in CMB lensing. We find larger differences in the matter power spectrum, reflecting the different values of $Ω_m$ resulting from the different partition of the dark sector into DM and DE, with only percent-level differences remaining once we compare $Ω_m^2P_m(k)$, indicating the importance of high-fidelity determinations of $Ω_m$. Our controlled comparison strategy can be a powerful tool for a wide range of models beyond $Λ$CDM.

astro-ph.CO↗

arXiv2026

Hubble tension: the shape wall

The standard "no-go theorem" against late-time solutions to the Hubble tension is essentially a normalization wall, since Baryon Acoustic Oscillation (BAO) measurements constrain the product $H_0r_d$, with $r_d$ the sound horizon at baryon drag. However, late-time solutions (which keep $r_d$ fixed) are tightly constrained not only by the BAO normalization $H_0r_d$, but also by the shape of the expansion history, i.e. the dimensionless expansion rate $E(z) \equiv H(z)/H_0$. We show that, if $r_d$ and the acoustic angular scale $θ_s$ are fixed, an increase in $H_0$ needs to be matched by an equal fractional increase in the dimensionless distance integral $I \equiv \int dz/E(z)$: $δH_0/H_0 \simeq δI/I$. We use this to quantify the "shape wall" set by relative distance constraints on $E(z)$, which we reconstruct nonparametrically, using Gaussian Processes and the latest unanchored Type Ia Supernovae (SNeIa) and BAO data. In our most conservative analysis using PantheonPlus SNeIa and DESI DR2 BAO data, we find a maximum fractional increase in $H_0$ of $\lesssim 2\%$, falling well short of the $\gtrsim 8\%$ required to solve the tension. This shape wall holds even in the presence of early-time new physics, and limits the maximum increase in $H_0$ which can be contributed by late-time modifications to $E(z)$ at fixed $θ_s$. Therefore, late-time modifications, whether invoked alone or alongside early-time new physics, face not only the well-known normalization wall, but also a stringent percent-level shape wall.

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arXiv2026

Running into tension: primordial black holes from ultra-slow-roll inflation, spectral running, and the Hubble tension

Single-field ultra-slow-roll (USR) inflation is among the most studied mechanisms for primordial black hole (PBH) formation. When a non-stationary inflection point close to CMB scales is present, these models predict a negative spectral running ($α_s<0$), whose magnitude increases with the PBH mass. This is in tension with recent hints for positive running from Atacama Cosmology Telescope (ACT) Cosmic Microwave Background (CMB) data. However, inflationary parameters inferred from CMB data are sensitive to the assumed pre-recombination expansion history, which is precisely where new physics motivated by the Hubble tension should operate. Focusing on axion-like early dark energy (EDE) as a benchmark, we investigate the effect of such pre-recombination new physics on $α_s$, and hence on the viability of USR PBH models, in light of state-of-the-art CMB data from Planck, ACT, and the South Pole Telescope, together with Baryon Acoustic Oscillation data from DESI DR2. Our analysis therefore provides an updated set of constraints on $α_s$ and the running of the running $β_s$. For most dataset combinations, moving from $Λ$CDM to EDE increases the inferred $α_s$: once the acoustic angular scale $θ_s$ is fixed, EDE increases the diffusion-to-acoustic angular scale ratio $θ_d/θ_s$, and the shift in $α_s$ compensates this extra damping by increasing small-scale power. In this sense, tension calls for tension: taking the Hubble tension seriously as an indication for new physics strengthens the challenges faced by USR PBH models. More broadly, our analysis stresses that inflationary model selection using CMB-inferred inflationary parameters such as $n_s$ and $α_s$ may be premature, especially until the Hubble tension, and more generally the pre-recombination expansion history, is understood.

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arXiv2026

Testing Scale-Dependent Suppression of Structure Growth in the Linear Regime

We investigate recent reports of a suppression in the growth rate of cosmic structures inferred from analyses of the $[fσ_8](z)$ dataset. To address this issue, we explore the hypothesis that the evolution of matter clustering is more accurately described within the framework of scale-dependent modified gravity. We perform a joint analysis of $[fσ_8](z)$, cosmic chronometer $H(z)$ measurements, luminosity distance data, and CMB observations using Markov Chain Monte Carlo techniques to constrain the parameters of a scale-dependent cosmological model and investigate its impact on the evolution of $[fσ_8](z)$. Our results indicate that the suppression of the growth rate of large-scale structures is more pronounced during the matter-dominated era than in the dark-energy-dominated epoch. We find evidence for scale-dependent growth at a statistical significance of $2.2\, σ$. In addition, we constrain the $S_8$ parameter and find it to be consistent with the value inferred from the CMB observations of the Planck Collaboration. Overall, our analysis shows that $k$-dependent growth models provide a viable explanation for the observed clustering of matter without exacerbating the current cosmological tensions.

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arXiv2026

High-redshift transverse BAO measurements with the SDSS quasar catalog

Transverse Baryon Acoustic Oscillation (BAO) measurements offer a robust geometric probe of the Universe expansion, presenting minimal dependence on fiducial cosmological models. In this work, we analyze the SDSS-DR16 quasar catalog to search for the 2D BAO signal in the unexplored redshift interval $1.5 \leq z \leq 2.0$. Performing a fine tomographic analysis in 50 thin disjoint redshift shells ($Δz = 0.01$), to suppress line-of-sight projection smearing, and incorporating a full analytical covariance matrix, we detect the acoustic peak in two uncorrelated redshift shells: $θ_{\rm BAO} = 1.911^{\circ} \pm 0.062^{\circ}$ and $θ_{\rm BAO} = 1.727^{\circ} \pm 0.081^{\circ}$ centered at $z_{\rm eff} = 1.725$ and $z_{\rm eff} = 1.775$, with statistical significances of $3.4\,σ$ and $3.0\,σ$, respectively. By introducing a dimensionless shift parameter $α$ in our empirical parameterization procedure, we then obtain two scaled angular diameter distances: $D_A/r_d = 11.00 \pm 0.36$ at $z_{\rm eff}=1.725$ and $D_A/r_d = 11.96 \pm 0.56$ at $z_{\rm eff}=1.775$. Incorporating these two novel data points into a literature compilation of 16 transverse BAO measurements, we perform a flat-$Λ$CDM parameter estimation, obtaining $Ω_{m,0} = 0.41 \pm 0.06$ and $h r_d = 99.3 \pm 2.0$ Mpc. Our measurements successfully bridge a significant observational gap at high redshift, which remain highly consistent with the constraints reported by the Planck and DESI collaborations, demonstrating the potential of quasar tomographic surveys for dynamical dark energy studies.

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arXiv2026

Physics-guided discovery of dynamical dark-energy equations of state through iterative AI reasoning

Phenomenological model building has traditionally relied on human reasoning: equations are proposed from theoretical intuition, analogy, or empirical convenience, and only then tested against data. Here we show that this cycle can be recast as an iterative AI reasoning process for dynamical dark energy. Our framework uses a large language model to propose equations of state together with cosmological rationales, grounded by retrieval from the dark-energy literature and refined through autonomous evaluation. Each candidate is embedded in a cosmological model, optimized against observations, and assessed using likelihood performance and theoretical consistency. An independent language-model critic scores the physical motivation, novelty, clarity, stability and implementation validity of both the equation and its rationale, allowing subsequent proposals to evolve jointly in mathematical structure and physical reasoning. Applied to cosmological data combinations including supernovae, baryon acoustic oscillations and Planck likelihoods, the framework identifies two parameterizations that, to the best of our knowledge, have not previously been explored and that are competitive with established forms. For Pantheon+ supernovae, DESI DR2 baryon acoustic oscillations and the full Planck 2018 temperature, polarization, and lensing likelihoods, the best AI-selected model attains larger Bayesian evidence than the traditional parameterizations considered here by more than one unit. These results show that AI-guided reasoning can complement physical model building by proposing and evaluating interpretable phenomenological parameterizations for dynamical dark energy.

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arXiv2026

Updated Cosmological Constraints from 2D BAO Measurements: A New Compilation and Comparison with DESI DR2

We investigate and update observational constraints on cosmological parameters within the $Λ$CDM and dynamical dark energy frameworks, using a new compilation of the transverse (or 2D) BAO data, measurements that provide a relatively model-independent estimate of the BAO angular scale at a given redshift. Firstly, we assess the consistency of this compilation with CMB-Planck data and recent BAO results from the DESI collaboration. After confirming minimal tension with CMB data, we perform a series of joint analyses combining CMB data with the 2D~BAO compilation, as well as with several recent Type Ia supernova (SNIa) samples. In all cases, we compare the constraining power of the 2D~BAO data with that of DESI~DR2 data (3D~BAO). Our results indicate that combining 2D~BAO with CMB and SNIa data provides observational constraints that are in agreement with those obtained using DESI~DR2 data. Although the precision of DESI~DR2 results remains higher, as expected due to the more accurate 3D measurements, the 2D~BAO compilation combined with other probes yields strong constraints. For example, in the $Λ$CDM context, we find (CMB + 2D~BAO): $H_0 = 68.16^{+0.41}_{-0.37} \,\,\, \text{km s}^{-1}\,\text{Mpc}^{-1}$ and $Σm_ν < 0.081~\mathrm{eV}$ (95\%~CL). These results are consistent with analogous analyses using DESI~DR2. Several other cases are investigated and discussed in the main text. Our results show that this new 2D~BAO compilation is robust and delivers meaningful cosmological constraints. Parameters from 2D~BAO alone agree with CMB-only results, with no significant tension. Overall, 2D and 3D BAO provide consistent and complementary information when combined with other probes.

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arXiv2025

Robust Evidence for Dynamical Dark Energy from DESI Galaxy-CMB Lensing Cross-Correlation and Geometric Probes

Recent analyses joining data from the Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations (BAO), and Type Ia Supernovae (SNIa) have provided strong evidence in favor of dynamical dark energy (DDE) over a simple cosmological constant. Motivated by these findings, we present new observational constraints on DDE based on the cross-correlation between DESI Luminous Red Galaxies (LRG) samples and CMB lensing ($\mathrm{CMB}_κ \times \mathrm{LRG}$), which effectively probes the impact of cosmological parameters on the growth of structure at the perturbative level. We demonstrate that, when combined with geometric measurements such as BAO and SNIa, this cross-correlation yields compelling statistical evidence for DDE exceeding $4σ$, including within simpler parametrizations such as the $w$CDM model. Remarkably, this evidence is independent of constraints from primary Planck CMB anisotropies data. These results highlight the robustness and potential of Galaxy-CMB lensing cross-correlation as a powerful observational probe of the dark sector, particularly when used in conjunction with geometric observables.

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arXiv2025

Challenging $Λ$CDM: 5$σ$ Evidence for a Dynamical Dark Energy Late-Time Transition

Recently, there has been considerable debate regarding potential evidence for the dynamical nature of dark energy (DE), particularly in light of Baryon Acoustic Oscillations (BAO) measurements released by DESI survey. In this work, we propose an agnostic test that simultaneously constrains the dark energy (DE) equation of state (EoS) and probes the possibility of a transition between the quintessence and phantom regimes, or vice versa. Our initial approach is independent of physical priors, allowing the data to determine which behavior best fits the parameters. We then consider a minimally modified gravity theory known as VCDM, into which we can map our initial approximation, placing it within a theoretically stable framework. To this end, we incorporate the most up-to-date datasets available, including BAO measurements from DESI-DR2, Type Ia Supernovae from the PantheonPlus, DESY5, and Union3 samples, as well as Cosmic Microwave Background (CMB) data from Planck. Our analysis reveals strong and statistically significant evidence for a quintessence-phantom transition across various data combinations. \textit{The strongest evidence is found for Planck+DESI+DESY5, with a significance exceeding $\sim$5$σ$ in favor of a quintessence-phantom transition at $z_† = 0.493^{+0.063}_{-0.081}$}. Beyond this redshift, the EoS remains within the phantom regime, while for $z < z_†$, it favors the quintessence regime. Despite this strong indication, \textit{we find that such transitions do not resolve the $H_0$ tension}

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arXiv2025

New constraints on interacting dark energy from DESI DR2 BAO observations

In its second data release (DR2), the Dark Energy Spectroscopic Instrument (DESI) publicly released measurements of Baryon Acoustic Oscillations (BAO) from over 13.1 million galaxies and 1.6 million quasars, covering the redshift range $0.295 \leq z \leq 2.330$. In this work, we investigate the impact of this new dataset on dark sector interaction models, which are motivated by non-gravitational interactions between dark energy (DE) and dark matter (DM), commonly referred to as interacting dark energy models (IDE). We focus on two frameworks: the traditional IDE model and the recently proposed sign-switching Interacting model (S-IDE), aiming to derive new and robust constraints on both scenarios. After carefully selecting the sample for the joint analysis, ensuring compatibility among the data without significant tension, our main results indicate that both models can alleviate the $H_0$ tension, reducing it to moderate tension approximately $2.7σ$. The IDE model shows compatibility with the latest $S_8$ constraints from cosmic shear surveys, while the S-IDE model predicts lower values of $S_8$, which align with alternative perspectives on the $S_8$ tension. For the traditional IDE model, we derive new bounds for the coupling parameter, marking the strongest constraints to date through geometric measurements. This highlights the crucial role that supernova samples can play in refining these constraints. For the S-IDE model, we find mild evidence (over $2σ$) for a non-zero coupling, once the PantheonPlus dataset calibrated with Cepheid-based magnitude measurements is included in the analysis.

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arXiv2025

Sign Switching in Dark Sector Coupling Interactions as a Candidate for Resolving Cosmological Tensions

The $Λ$CDM model has successfully explained a wide range of cosmological observations, but is increasingly challenged by the emergence of cosmological tensions, particularly the Hubble Tension $H_0$ and the $S_8$ tension. The Hubble Tension, with a significance above 5$σ$, and the $S_8$ tension, showing a discrepancy of approximately 2-4$σ$, highlight inconsistencies between measurements of the local and early universe. This paper expands a well-established Interacting Dark Energy (IDE) phenomenological scenario, where dark matter (DM) can transfer energy to dark energy (DE) or vice versa, depending on the sign of the coupling parameter $ξ$. The novel feature consists in a transition mechanism which reverses the direction of the energy-momentum transfer after the redshift where the densities of the dark species are the same. We evaluate this model using a comprehensive set of recent observational data, including Baryon Acoustic Oscillations (BAO) from the DESI survey, Type Ia Supernovae from the PantheonPlus, DESY5 and Union3 samples, and Cosmic Microwave Background (CMB) data from Planck. Our analysis shows that this scenario can potentially relax both the $H_0$ and $S_8$ tensions simultaneously. We find the new model to be weakly preferred over $Λ$CDM by BAO-DESI data. However, we show that the IDE model features positive Bayesian evidence compared to $Λ$CDM only when Cepheid distance calibration in the SH0ES sample is used to calibrate SNIa data from PantheonPlus.

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arXiv2024

Interacting Dark Energy after DESI Baryon Acoustic Oscillation measurements

We investigate the implications of the Baryon Acoustic Oscillations measurement released by the Dark Energy Spectroscopic Instrument (DESI) for Interacting Dark Energy (IDE) models characterized by an energy-momentum flow from Dark Matter to Dark Energy. By combining Planck-2018 and DESI data, we observe a preference for interactions, leading to a non-vanishing interaction rate $ξ=-0.32^{+0.18}_{-0.14}$, which results in a present-day expansion rate $H_0=70.8^{+1.4}_{-1.7}$ km/s/Mpc, reducing the tension with the value provided by the SH0ES collaboration to less than $\sim 1.3 σ$. The preference for interactions remains robust when including measurements of the expansion rate $H(z)$ obtained from the relative ages of massive, early-time, and passively-evolving galaxies, as well as when considering distance moduli measurements from Type-Ia Supernovae sourced from the Pantheon-plus catalog using the SH0ES Cepheid host distances as calibrators. Overall, the IDE framework provides an equally good, or better, explanation of both high- and low-redshift background observations compared to $Λ$CDM, while also yielding higher $H_0$ values that align more closely with the local distance ladder estimates. However, a limitation of the IDE model is that it predicts lower $Ω_{m}$ and higher $σ_{8}$ values, which may not be fully consistent with large-scale structure data at the perturbation level.

astro-ph.CO↗

arXiv2024

Quantifying the $S_8$ tension and evidence for interacting dark energy from redshift-space distortion measurements

In recent years, Cosmic Microwave Background (CMB) observations, Weak Lensing surveys, and $fσ_8(z)$ measurements from Redshift-Space Distortions (RSD) have revealed a significant ($\sim$3$-$5$σ$) discrepancy in the inferred value of the matter clustering parameter $S_8$. In this work, we investigate the implications of RSD for a cosmological framework postulating an interaction between Dark Energy (DE) and Dark Matter (DM). We explore scenarios where DM can transfer energy-momentum to DE or vice versa. The energy-momentum flow is characterized by the strength and the sign of the coupling parameter $ξ$. Our baseline analysis combines RSD measurements with the latest data from Baryon Acoustic Oscillations (BAO) observed by DESI, Type Ia Supernovae from the PantheonPlus sample, and CMB data from Planck. We demonstrate that RSD measurements provide significant additional information imposing new and strong upper bounds on possible interaction in the dark sector. Models with $ξ> 0$ can effectively alleviate the tension in $S_8$, presenting them as compelling alternatives.

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arXiv2024

Exploring new physics in the late Universe's expansion through non-parametric inference

In this study, we investigate deviations from the Planck-$Λ$CDM model in the late universe ($z \lesssim 2.5$) using the Gaussian Processes method, with minimal assumptions. Our goal is to understand where exploring new physics in the late universe is most relevant. We analyze recent Cosmic Chronometers (CC), Type Ia Supernovae (SN), and Baryon Acoustic Oscillations (BAO) data. By examining reconstructions of the dimensionless parameter $δ(z)$, which measures deviations of the Hubble parameter from the Planck-$Λ$CDM predictions, we identify intriguing features at low ($z \lesssim 0.5$) and high ($z \gtrsim 2$) redshifts. Deviations from the Planck-$Λ$CDM model were not significant between $0.5\lesssim z \lesssim2$. Using the combined CC+SN+BAO dataset, we gain insights into dark energy (DE) dynamics, resembling characteristics of omnipotent DE, extending beyond quintessence and phantom models. DE exhibits n-quintessence traits for $z\gtrsim2$, transitioning with a singularity around $z\sim2$ to usual phantom traits in $1\lesssim z\lesssim2$. DE characteristics differ between scenarios ($H_0$-SH0ES and $H_0$-$Λ$\&CMB), with $H_0$-SH0ES leaning towards phantom traits and $H_0$-$Λ$\&CMB towards quintessence. We suggest exploring new physics at $z\lesssim0.5$ and $1.5\lesssim z\lesssim2.5$, particularly around $z = 2$, to understand cosmological tensions such as $H_0$ and $S_8$.

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