arXiv subjects

Rodrigo von Marttens

Publications and source records attributed to Rodrigo von Marttens.

At least 19 recordsLinked to original sources

arXiv2026

Renormalization group corrections to $Λ$CDM model and observational consequences for $H_0$ tension

We explore the renormalization group-based extension of the $Λ$CDM model as a potential solution to the current cosmological tensions. In this approach, both the cosmological constant density and Newton's constant are allowed to vary with the energy scale, as a consequence of the remnant effects of massive quantum fields in the low-energy regime. The corresponding cosmological model is consistent with the principles of quantum field theory, based on the covariance of the vacuum effective action, and is characterized by an unique extra parameter $ν$. Our analysis yields a best-fit value of $ν= - (2.5 \pm 1.3)\times 10^{-4}$, placing the $Λ$CDM limit at the $2σ$ region of the $ν$ posterior. This narrow range is consistent with data from CMB (Planck), BAO (DESI), and SN Ia (DES Y5). Our result also alleviates the $H_0$ tension and is consistent with the previously established constraints from large-scale structure. In these kind of models, there is a link between cosmology and particle physics. Our results point to possibility of a new physics, characterized by a mass spectrum lying below the Planck scale but above the values typically associated with Grand Unified Theories (GUTs).

astro-ph.CO↗

arXiv2026

Standard Perturbation Theory for Interacting Dark Sector cosmologies I: Breakdown of Einstein de Sitter kernels

Interacting dark sector (IDS) models provide a commonly explored extension of the standard $Λ$CDM cosmology, allowing for non-gravitational energy--momentum exchange between cold dark matter (CDM) and dark energy (DE). Although such models can be constructed to reproduce the same background expansion history as $Λ$CDM, their impact on the growth of cosmic structures is fundamentally different and requires a careful treatment of cosmological perturbations. In this work, we develop the one-loop Standard Perturbation Theory (SPT) formalism for IDS cosmologies without invoking the Einstein--de~Sitter (EdS) approximation. We show that even weak dark sector interactions induce a non-trivial time dependence in the perturbative kernels, leading to a breakdown of the EdS approximation commonly assumed in $Λ$CDM analyses. By deriving and numerically solving the evolution equations for the second- and third-order kernels, we compute the corresponding one-loop corrections to the matter power spectrum and find that the resulting deviations can significantly exceed the percent level, even for small interaction strengths. Our results demonstrate that nonlinear corrections are systematically enhanced in IDS models and that neglecting the full time dependence of the kernels can lead to biased predictions on mildly nonlinear scales. These findings establish the necessity of a time-dependent perturbative treatment for IDS scenarios and provide a robust framework for precision tests using nonlinear large-scale structure (LSS) observables.

astro-ph.CO↗

arXiv2026

Dark Degeneracy in DESI DR2: Interacting or Evolving Dark Energy?

The standard $Λ$CDM model, despite its success, is challenged by persistent observational tensions in the Hubble constant ($H_0$) and the matter clustering amplitude ($S_8$), motivating the exploration of alternative cosmological scenarios. We investigate a dark energy model with a phenomenological interaction in the dark sector, constructed to be exactly degenerate at the background level with the Chevallier-Polarski-Linder (CPL) parameterization. This setup allows us to test whether models with identical expansion histories but distinct physical mechanisms can be distinguished by cosmological data. We perform a Bayesian analysis using a combination of recent datasets: DESI DR2 BAO measurements, DESY5 supernovae, and CMB data from Planck and ACT. We find that both the interacting model and the CPL model provide significantly better fits to the data than $Λ$CDM. Although indistinguishable in background observables, the interacting model predicts a distinct matter-sector evolution driven by a late-time sign change in the dark sector interaction at $z \approx 0.8$, corresponding to the $w=-1$ crossing in the CPL description. In this sense, the interacting picture may be considered more physical, since it avoids the problematic crossing by construction. The resulting decay of dark energy into dark matter lowers $S_8$, potentially alleviating the weak-lensing $S_8$ tension. At the same time, it predicts a sharp suppression of the growth rate $fσ_8(z)$ at $z \lesssim 0.8$, which is in tension with current measurements of structure formation. This indicates that the model may not simultaneously reconcile the expansion history and the observed growth of cosmic structure, highlighting the need for a more comprehensive analysis to fully assess its viability.

astro-ph.CO↗

arXiv2025

Total and dark mass from observations of galaxy centers with Machine Learning

The galaxy total mass inside the effective radius encode important information on the dark matter and galaxy evolution model. Total "central" masses can be inferred via galaxy dynamics or with gravitational lensing, but these methods have limitations. We propose a novel approach, based on Random Forest, to make predictions on the total and dark matter content of galaxies using simple observables from imaging and spectroscopic surveys. We use catalogs of multi-band photometry, sizes, stellar mass, kinematic "measurements" (features) and dark matter (targets) of simulated galaxies, from Illustris-TNG100 hydrodynamical simulation, to train a Mass Estimate machine Learning Algorithm (Mela). We separate the simulated sample in passive early-type galaxies (ETGs), both "normal" and "dwarf", and active late-type galaxies (LTGs) and show that the mass estimator can accurately predict the galaxy dark masses inside the effective radius in all samples. We finally test the mass estimator against the central mass estimates of a series of low redshift (z$\leq$0.1) datasets, including SPIDER, MaNGA/DynPop and SAMI dwarf galaxies, derived with standard dynamical methods based on Jeans equations. Dynamical masses are reproduced within 0.30 dex ($\sim2σ$), with a limited fraction of outliers and almost no bias. This is independent of the sophistication of the kinematical data collected (fiber vs. 3D spectroscopy) and the dynamical analysis adopted (radial vs. axisymmetric Jeans equations, virial theorem). This makes Mela a powerful alternative to predict the mass of galaxies of massive stage-IV surveys' datasets.

astro-ph.GA↗

arXiv2025

The miniJPAS and J-NEP surveys: Machine learning for star-galaxy separation

We present a supervised machine learning classification of sources from the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) Pathfinder datasets: miniJPAS and J-NEP. Leveraging crossmatches with spectroscopic and photometric catalogs, we construct a robust labeled dataset comprising 14594 sources classified into extended (galaxies) and point-like (stars and quasars) objects. We assess dataset representativeness using UMAP analysis, confirming broad and consistent coverage of feature space. An XGBoost classifier, with hyperparameters tuned using automated optimization, is trained using purely photometric data (60-band J-PAS magnitudes) and combined photometric and morphological features, with performance thoroughly evaluated via ROC and purity-completeness metrics. Incorporating morphology significantly improves classification, outperforming the baseline classifications available in the catalogs. Permutation importance analysis reveals morphological parameters, particularly concentration, normalized peak surface brightness, and PSF, alongside photometric features around 4000 and 6900 A, as crucial for accurate classifications. We release a value-added catalog with our models for star-galaxy classification, enhancing the utility of miniJPAS and J-NEP for subsequent cosmological and astrophysical analyses.

astro-ph.IM↗

arXiv2025

Reconstructing the redshift evolution of Type Ia supernovae absolute magnitude

This work investigates a potential time dependence of the absolute magnitude of Type Ia Supernovae (SN Ia). Employing the Gaussian Process approach, we obtain the SN Ia absolute magnitude and its derivative as a function of redshift. The data set considered in the analysis comprises measurements of apparent magnitude from SN Ia, Hubble rate from cosmic chronometers, and the ratio between angular and radial distances from Large-Scale Structure data (BAO and voids). Our findings reveal good compatibility between the reconstructed SN Ia absolute magnitudes and a constant value. However, the mean value obtained from the Gaussian Process reconstruction is $M=-19.456\pm 0.059$, which is $3.2σ$ apart from local measurements by Pantheon+SH0ES. This incompatibility may be directly associated to the $Λ$CDM model and local data, as it does not appear in either model-dependent or model-independent estimates of the absolute magnitude based on early universe data. Furthermore, we assess the implications of a variable $M$ within the context of modified gravity theories. Considering the local estimate of the absolute magnitude, we find $\sim3σ$ tension supporting departures from General Relativity in analyzing scenarios involving modified gravity theories with variations in Planck mass through Newton's constant.

astro-ph.CO↗

arXiv2025

The catalogue of virtual early-type galaxies from IllustrisTNG: validation and real observation consistency

Early-type galaxies (ETGs) are reference systems to understand galaxy formation and evolution processes. The physics of their formation and internal dynamics are codified in well-known scaling relations. In this context, cosmological hydrodynamical simulations play an important role in probing the physical origins of scaling relations by providing a controlled environment to study the formation and evolution of galaxies, linking their internal dynamics to underlying physical processes, and testing the robustness of observational inference methods. In this work, we present the closest-to-reality sample of ETGs from the IllustrisTNG100-1 simulation, dubbed "virtual-ETGs", based on an observational-like algorithm that combines standard projected and three-dimensional galaxy structural parameters. We extract 2D photometric information by projecting the galaxies' light into three planes and modelling them via Sérsic profiles. Aperture velocity dispersions, corrected for softened central dynamics, are calculated along the line-of-sight orthogonal to the photometric projection plane. Central mass density profiles assume a power-law model, while 3D masses remain unmodified from the IllustrisTNG catalogue. The final catalogue includes $10121$ galaxies at redshifts $z \leq 0.1$. By comparing the virtual properties with observations, we find that the virtual-ETG scaling relations (e.g., size-mass, size-central surface brightness, and Faber-Jackson), central density slopes, and scaling relations among total density slopes and galaxy structural parameters are generally consistent with observations. We make the virtual-ETG publicly available for galaxy formation studies and plan to use this sample as a training set for machine learning tools to infer galaxy properties in future imaging and spectroscopic surveys.

astro-ph.GA↗

arXiv2025

Scale-dependent and background-preserving gravity from an action: cosmological tests

We investigate the observational implications of a gravitational model wherein the gravitational constant $G$ and the cosmological constant $Λ$ exhibit scale-dependent behavior at the perturbative level, while preserving the General Relativity (GR) field equations at the background. This model is motivated by the potential influence of large-scale (infrared) Renormalization Group (RG) corrections to gravity and is constructed upon an effective action incorporating a scale definition via Lagrange multipliers. We explore the effects of these modifications during the recombination epoch with particular focus on their impact on the structure of acoustic oscillations. Additionally, we perform a comprehensive parameter fitting analysis using data from the Cosmic Microwave background (CMB), type Ia Supernovae (SN Ia), Baryon Acoustic Oscilations (BAO) and Redshift Space Distortions (RSD). Our results indicate that the RG corrections here considered are consistent with the main predictions of the $Λ$CDM model, and they slightly increase the uncertainties in the parameter estimations. Such small differences cannot be used to dismiss the current cosmological tensions. Although previous results indicated that this model is more flexible than $Λ$CDM regarding RSD data, potentially alleviating tensions, this advantage becomes negligible with the current extended data set. The framework maintains its theoretical consistency and foundation; however, unless further generalized, it cannot effectively address current cosmological issues.

gr-qc↗

arXiv2025

Interacting dark sector with quadratic coupling: theoretical and observational viability

Models proposing a non-gravitational interaction between dark energy (DE) and dark matter (CDM) have been extensively studied as alternatives to the standard cosmological model. A common approach to describing the DE-CDM coupling assumes it to be linearly proportional to the dark energy density. In this work, we consider the model with interaction term $Q=3Hγ{ρ_{x}^{2}}/{(ρ_{c}+ρ_{x})}$. We show that for positive values of $γ$ this model predicts a future violation of the Weak Energy Condition (WEC) for the dark matter component, and for a specific range of negative values of $γ$ the CDM energy density can be negative in the past. We perform a parameter selection analysis for this model using data from Type Ia supernovae from the Pantheon sample, $H(z)$ measurements from the Cosmic Chronometers sample, Baryon Acoustic Oscillations from the DESI survey, and Cosmic Microwave Background data from the Planck combined with the Hubble constant $H_0$ prior. Imposing a prior to ensure that the WEC is not violated, our model is consistent with $Λ$CDM in 2$σ$ C.L., yet exhibits a preference for smaller values of $σ_8$, alleviating the $σ_8$ tension between the CMB results from Planck 2018 and the weak gravitational lensing observations from the KiDS-1000 cosmic shear survey.

astro-ph.CO↗

arXiv2025

Dark energy and cosmic acceleration

The discovery that we live in an accelerating universe changed drastically the paradigm of physics and introduced the concept of \textit{dark energy}. In this work, we present a brief historical description of the main events related to the discovery of cosmic acceleration and the basic elements of theoretical and observational aspects of dark energy. Regarding the historical perspective, we outline some of the key milestones for tracing the journey from Einstein's proposal of the cosmological constant to the type Ia supernovae results. Conversely, on the theoretical/observational side, we begin by analyzing cosmic acceleration within the context of the standard cosmological model, i.e., in terms of the cosmological constant. In this case, we show how a positive cosmological constant drives accelerated expansion and discuss the main observational aspects, such as updated results and current cosmological tensions. We also explore alternative descriptions of dark energy, encompassing dynamic and interacting dark energy models.

astro-ph.CO↗

arXiv2024

CMB constraints on inflection-point inflation with a pseudo-scalar dark matter

In this work, we investigate the physical aspects of the inflection-point inflation scenario and assess its observational viability in light of current Cosmic Microwave Background (CMB) data. The model we consider encapsulates the inflaton with a pseudo-scalar (the dark matter candidate) in a complex neutral scalar singlet. The cosmological constraints on the parameters of inflation derived at a high energy scale are translated to a low energy scale by running these parameters. Ensuring the entire Lagrangian to be invariant under a $Z_3$ symmetry with the adequate transformation of the fields, the imaginary part of the singlet decouples from the other scalars of the model. We then investigate if the observational viability of inflation is also compatible with this pseudo-scalar being the dark matter component.We show that the CMB constraints on the inflationary parameters assure that the pseudo-scalar is stable and provides the correct relic dark matter abundance only when the pseudo-scalar is thermally produced.

astro-ph.CO↗

arXiv2024

Assessing the dark degeneracy through the gas mass fraction data

It is well-known that Einstein's equations constrain only the total energy-momentum tensor of the cosmic substratum, without specifying the characteristics of its individual constituents. Consequently, cosmological models featuring distinct decompositions within the dark sector, while sharing identical values for the sum of dark components' energy-momentum tensor, remain indistinguishable when assessed through observables based on distance measurements. Notably, it has been already demonstrated that cosmological models with dynamical descriptions of dark energy, characterized by a time-dependent equation of state (EoS), can always be mapped into a model featuring a decaying vacuum ($w=-1$) coupled with dark matter. We explore the possibility of breaking this degeneracy by using measurements of the gas mass fraction observed in massive and relaxed galaxy clusters. This data is particularly interesting for this purpose because it isolates the matter contribution, possibly allowing the degeneracy breaking. We study the particular case of the $w$CDM model with its interactive counterpart. We compare the results obtained from both descriptions with a non-parametric analysis obtained through Gaussian Process. Even though the degeneracy may be broken from the theoretical point of view, we find that current gas mass fraction data seems to be insufficient for a final conclusion about which approach is favored, even when combined with SNIa, BAO and CMB.

astro-ph.CO↗

arXiv2022

One-parameter dynamical dark-energy from the generalized Chaplygin gas

The fact that Einstein's equations connect the space-time geometry to the total matter content of the cosmic substratum, but not to individual contributions of the matter species, can be translated into a degeneracy in the cosmological dark sector. Such degeneracy makes it impossible to distinguish cases where dark energy (DE) interacts with dark matter (DM) from a dynamical non-interacting scenario using observational data based only on time or distance measurements. In this paper, based on the non-adiabatic generalized Chaplygin gas (gCg) model, we derive and study some cosmological consequences of a varying one-parameter dynamical DE parameterization, which does not allow phantom crossing. We perform a parameter selection using the most recent public available data, such as the data from Planck 2018, eBOSS DR16, Pantheon and KiDS-1000. We find that current observations provide strong constraints on the model parameters, leading to values very close to the $Λ$CDM cosmology, at the same time that the well-known $σ_8$ tension is reduced from $\sim 3σ$ to $\sim 1σ$ level.

astro-ph.CO↗

arXiv2021

A Test of the Standard Cosmological Model with Geometry and Growth

We perform a general test of the $Λ{\rm CDM}$ and $w {\rm CDM}$ cosmological models by comparing constraints on the geometry of the expansion history to those on the growth of structure. Specifically, we split the total matter energy density, $Ω_M$, and (for $w {\rm CDM}$) dark energy equation of state, $w$, into two parameters each: one that captures the geometry, and another that captures the growth. We constrain our split models using current cosmological data, including type Ia supernovae, baryon acoustic oscillations, redshift space distortions, gravitational lensing, and cosmic microwave background (CMB) anisotropies. We focus on two tasks: (i) constraining deviations from the standard model, captured by the parameters $ΔΩ_M \equiv Ω_M^{\rm grow}-Ω_M^{\rm geom}$ and $Δw \equiv w^{\rm grow}-w^{\rm geom}$, and (ii) investigating whether the $S_8$ tension between the CMB and weak lensing can be translated into a tension between geometry and growth, i.e. $ΔΩ_M \neq 0$, $Δw \neq 0$. In both the split $Λ{\rm CDM}$ and $w {\rm CDM}$ cases, our results from combining all data are consistent with $ΔΩ_M = 0$ and $Δw = 0$. If we omit BAO/RSD data and constrain the split $w {\rm CDM}$ cosmology, we find the data prefers $Δw<0$ at $3.6σ$ significance and $ΔΩ_M>0$ at $4.2σ$ evidence. We also find that for both CMB and weak lensing, $ΔΩ_M$ and $S_8$ are correlated, with CMB showing a slightly stronger correlation. The general broadening of the contours in our extended model does alleviate the $S_8$ tension, but the allowed nonzero values of $ΔΩ_M$ do not encompass the $S_8$ values that would point toward a mismatch between geometry and growth as the origin of the tension.

astro-ph.CO↗

arXiv2021

Inferring galaxy dark halo properties from visible matter with Machine Learning

Next-generation surveys will provide photometric and spectroscopic data of millions to billions of galaxies with unprecedented precision. This offers a unique chance to improve our understanding of the galaxy evolution and the unresolved nature of dark matter (DM). At galaxy scales, the density distribution of DM is strongly affected by the astrophysical feedback processes, which are difficult to fully account for in classical techniques to derive mass models. In this work, we explore the capability of supervised learning algorithms to predict the DM content of galaxies from luminous observational-like parameters, using the public catalog of the TNG100 simulation. In particular, we use Photometric, Structural and Kinematic parameters to predict the total DM mass, DM half-mass radius, DM mass inside one and two stellar half-mass radii. We adopt the coefficient of determination, $R^2$, as a reference metric to evaluate the accuracy of these predictions. We find that the Photometric features alone are able to predict the total DM mass with fair accuracy, while Structural and Photometric features together are more effective to determine the DM inside the stellar half mass radius, and the DM within twice the stellar half mass radius. However, using all observational quantities together (Photometry, Structural and Kinematics) incredibly improves the overall accuracy for all DM quantities. This first test shows that Machine Learning tools are promising approaches to derive predictions of the DM in real galaxies. The next steps will be to improve observational realism of the training sets, by closely select samples which accurately reproduce the typical observed luminous scaling relations. The trained pipelines will be suitable for real galaxy data collected from the next-generation surveys like Rubin/LSST, Euclid, CSST, 4MOST, DESI, to derive, e.g., the properties of their central DM fractions.

astro-ph.GA↗

arXiv2021

A model-independent reconstruction of dark sector interactions

Relaxing the conventional assumption of a minimal coupling between the dark matter (DM) and dark energy (DE) fields introduces significant changes in the predicted evolution of the Universe. Therefore, testing such a possibility constitutes an essential task not only for cosmology but also for fundamental physics. In a previous communication [Phys. Rev. D99, 043521, 2019], we proposed a new null test for the $Λ$CDM model based on the time dependence of the ratio between the DM and DE energy densities which is also able to detect potential signatures of interaction between the dark components. In this work, we extend that analysis avoiding the $ Λ$CDM assumption and reconstruct the interaction in the dark sector in a fully model-independent way using data from type Ia supernovae, cosmic chronometers and baryonic acoustic oscillations. According to our analysis, the $Λ$CDM model is consistent with our model-independent approach at least at $3σ$ CL over the entire range of redshift studied. On the other hand, our analysis shows that the current background data do not allow us to rule out the existence of an interaction in the dark sector. Finally, we present a forecast for next-generation LSS surveys. In particular, we show that Euclid and SKA will be able to distinguish interacting models with about 4\% of precision at $z\approx 1$.

astro-ph.CO↗

arXiv2021

Testing the consistency between cosmological data: the impact of spatial curvature and the dark energy EoS

The results of joint analyses of available cosmological data have motivated an important debate about a possible detection of a non-zero spatial curvature. If confirmed, such a result would imply a change in our present understanding of cosmic evolution with important theoretical and observational consequences. In this paper we discuss the legitimacy of carrying out joint analyses with the currently available data sets and explore their implications for a non-flat universe and extensions of the standard cosmological model. We use a robust tension estimator to perform a quantitative analysis of the physical consistency between the latest data of Cosmic Microwave Background, type Ia supernovae, Baryonic Acoustic Oscillations and Cosmic Chronometers. We consider the flat and non-flat cases of the $Λ$CDM cosmology and of two dark energy models with a constant and varying dark energy EoS parameter. The present study allows us to better understand if possible inconsistencies between these data sets are significant enough to make the results of their joint analyses misleading, as well as the actual dependence of such results with the spatial curvature and dark energy parameterizations.

astro-ph.CO↗

arXiv2020

Dark degeneracy I: Dynamical or interacting dark energy?

We revisit the dark degeneracy that arises from the Einstein equations relating geometry to the total cosmic substratum but not resolving its individual components separately. We establish the explicit conditions for the dark degeneracy in the fluid description of the dark sector. At the background level, this degeneracy can be formally understood in terms of a unified dark sector Equation of State (EoS) that depends both on the dynamical nature of the dark energy (DE) as well as on its interaction with the pressureless dark matter. For linear perturbations, the degeneracy arises for specified DE pressure perturbations (or sound speed, equivalently) and DE anisotropic stress. Specializing to the degeneracy between non-interacting dynamical DE and interacting vacuum DE models, we perform a parameter estimation analysis for a range of dynamical DE parametrizations, where for illustration we explicitly break the degeneracy at the linear level by adopting a luminal sound speed for both scenarios. We conduct this analysis using cosmological background data alone and in combination with Planck measurements of the cosmic microwave background radiation. We find that although the overall phenomenology between the dynamical DE and interacting approaches is similar, there are some intriguing differences. In particular, there is an ambiguity in the strength of constraints on $Ω_{m0}$ and $σ_8$, which are considerably weakened for interacting vacuum DE, indicating that the dark degeneracy can change the significance of tensions in cosmological parameters inferred from different data sets.

astro-ph.CO↗