arXiv subjects

Eleonora Di Valentino

Publications and source records attributed to Eleonora Di Valentino.

At least 109 records · Page 6Linked to original sources

arXiv2024

Testing $α$-attractor quintessential inflation against CMB and low-redshift data

Due to universality and attractor properties, $α$-attractor quintessential inflation establishes direct relations between inflationary observables such as the scalar tilt $n_s$ and the tensor-to-scalar ratio $r$, and late-time dark energy equation of state parameters $w_0$ and $w_a$. In this work, we examine three different physically motivated regimes, considering complete freedom in the parameter $α$, models inspired by supergravity where $α$ takes on values up to $α=7/3$, and Starobinsky inflation ($α=1$). We investigate the consistency and constraints imposed by Cosmic Microwave Background measurements from the Planck satellite, B-mode polarization data from the BICEP/Keck collaboration, and low-redshift observations. Additionally, we consider small-scale CMB measurements released by the Atacama Cosmology Telescope, which give results approaching the Harrison-Zel'dovich spectrum ($n_s \approx 1$). Here $α$-attractors lead to an improved fit over $Λ$CDM. For the large-scale CMB measurements, $α\gtrsim2$ models can provide equally good fits as $Λ$CDM.

astro-ph.CO↗

arXiv2024

Exploring the Growth Index $γ_L$: Insights from Different CMB Dataset Combinations and Approaches

In this study we investigate the growth index $γ_L$, which characterizes the growth of linear matter perturbations, while analysing different cosmological datasets. We compare the approaches implemented by two different patches of the cosmological solver CAMB: MGCAMB and CAMB_GammaPrime_Growth. In our analysis we uncover a deviation of the growth index from its expected $Λ$CDM value of $0.55$ when utilizing the Planck dataset, both in the MGCAMB case and in the CAMB_GammaPrime_Growth case, but in opposite directions. This deviation is accompanied by a change in the direction of correlations with derived cosmological parameters. However, the incorporation of CMB lensing data helps reconcile $γ_L$ with its $Λ$CDM value in both cases. Conversely, the alternative ground-based telescopes ACT and SPT consistently yield growth index values in agreement with $γ_L=0.55$. We conclude that the presence of the A$_{\mathrm{lens}}$ problem in the Planck dataset contributes to the observed deviations, underscoring the importance of additional datasets in resolving these discrepancies.

astro-ph.CO↗

arXiv2024

A new binning method to choose a standard set of Quasars

Although the Lambda Cold Dark Matter model is the most accredited cosmological model, information at intermediate redshifts (z) between type Ia Supernovae (z = 2.26) and the Cosmic Microwave Background (z = 1100) is crucial to validate this model further. Here, we present a detailed and reliable methodology for binning the quasars (QSO) data that allows the identification of a golden sample of QSOs to be used as standard candles. This procedure has the advantage of being very general. Thus, it can be applied to any astrophysical sources at cosmological distances. This methodology allows us to avoid the circularity problem since it involves a flux-flux relation and includes the analysis of removing selection biases and the redshift evolution. With this method, we have discovered a sample of 1253 quasars up to z = 7.54 with reduced intrinsic dispersion of the relation between Ultraviolet and X-ray fluxes, with $δ_{int} = 0.096\pm 0.003$ (56\% less than the original sample where $δ_{int} =0.22$). Once the luminosities are corrected for selection biases and redshift evolution, this `gold' sample allows us to determine the matter density parameter to be $Ω_M=0.240 \pm 0.064$. This value is aligned with the results of the $ΛCDM$ model obtained with SNe Ia.

astro-ph.HE↗

arXiv2024

Omnipotent dark energy: A phenomenological answer to the Hubble tension

This paper introduces the class of omnipotent dark energy (DE) models characterized by nonmonotonic energy densities that are capable of attaining negative values with corresponding equation of state parameters featuring phantom divide line (PDL) crossings and singularities. These nontrivial features are phenomenologically motivated by findings of previous studies that reconstruct cosmological functions from observations, and the success of extensions of $Λ$CDM, whose actual or effective DE density is omnipotent, in alleviating the observational discordance within $Λ$CDM. As an example, we focus on one embodiment of omnipotent DE, viz., the DE parametrization introduced in Di Valentino et al. [Dark energy with phantom crossing and the H0 tension, Entropy 23, 404 (2021)] (DMS20). By updating and extending the datasets used in the original paper where it was introduced, we confirm the effectiveness of DMS20 in alleviating the observational discrepancies. Additionally, we uncover that its negative DE density feature, importance of which was not previously investigated, plays a crucial role in alleviating the tensions, along with the PDL crossing feature that the parametrization presupposes. In particular, we find that there is a positive correlation between the $H_0$ parameter and the scale ($a_p$) at which DE density transitions from negative to positive, in agreement with previous studies that incorporate this transition feature. For our full dataset, the model yields $H_0=70.05 \pm 0.64$ (68% CL) relaxing the $H_0$ tension with a preference of crossing to negative DE densities ($a_p>0$ at 99% CL), along with the constraint $a_m=0.922^{+0.041}_{-0.035}$ on the scale of the presupposed PDL crossing.

astro-ph.CO↗

arXiv2023

Tracking the Multifield Dynamics with Cosmological Data: A Monte Carlo approach

We introduce a numerical method specifically designed for investigating generic multifield models of inflation where a number of scalar fields $ϕ^K$ are minimally coupled to gravity and live in a field space with a non-trivial metric $G_{IJ}(ϕ^K)$. Our algorithm consists of three main parts. Firstly, we solve the field equations through the entire inflationary period, deriving predictions for observable quantities such as the spectrum of scalar perturbations, primordial gravitational waves, and isocurvature modes. We also incorporate the transfer matrix formalism to track the behavior of adiabatic and isocurvature modes on super-horizon scales and the transfer of entropy to scalar modes after the horizon crossing. Secondly, we interface our algorithm with Boltzmann integrator codes to compute the subsequent full cosmology, including the cosmic microwave background anisotropies and polarization angular power spectra. Finally, we develop a novel sampling algorithm able to efficiently explore a large volume of the parameter space and identify a sub-region where theoretical predictions agree with observations. In this way, sampling over the initial conditions of the fields and the free parameters of the models, we enable Monte Carlo analysis of multifield scenarios. We test all the features of our approach by analyzing a specific model and deriving constraints on its free parameters. Our methodology provides a robust framework for studying multifield inflation, opening new avenues for future research in the field.

astro-ph.CO↗

arXiv2023

On the dynamics of a dark sector coupling

Interacting dark energy models may play a crucial role in explaining several important observational issues in modern cosmology and also may provide a solution to current cosmological tensions. Since the phenomenology of the dark sector could be extremely rich, one should not restrict the interacting models to have a coupling parameter which is constant in cosmic time, rather allow for its dynamical behavior, as it is common practice in the literature when dealing with other dark energy properties, as the dark energy equation of state. We present here a compendium of the current cosmological constraints on a large variety of interacting models, investigating scenarios where the coupling parameter of the interaction function and the dark energy equation of state can be either constant or dynamical. For the most general schemes, in which both the coupling parameter of the interaction function and the dark energy equation of state are dynamical, we find $95\%$~CL evidence for a dark energy component at early times and slightly milder evidence for a dynamical dark coupling for the most complete observational data set exploited here, which includes CMB, BAO and Supernova Ia measurements. Interestingly, there are some cases where a dark energy component different from the cosmological constant case at early times together with a coupling different from zero today, can alleviate both the $H_0$ and $S_8$ tension for the full dataset combination considered here. Due to the energy exchange among the dark sectors, the current values of the matter energy density and of the clustering parameter $σ_8$ are shifted from their $Λ$CDM-like values. This fact makes future surveys, especially those focused on weak lensing measurements, unique tools to test the nature and the couplings of the dark energy sector.

astro-ph.CO↗

arXiv2023

Lensing impact on cosmic relics and tensions

Cosmological bounds on neutrinos and additional hypothetical light thermal relics, such as QCD axions, are currently among the most restrictive ones. These limits mainly rely on Cosmic Microwave Background temperature anisotropies. Nonetheless, one of the largest cosmological signatures of thermal relics is that on gravitational lensing, due to their free streaming behavior before their non-relativistic period. We investigate late time only hot relic mass constraints, primarily based on recently released lensing data from the Atacama Cosmology Telescope, both alone and in combination with lensing data from the Planck Satellite. Additionally, we consider other local probes, such as Baryon Acoustic Oscillations measurements, shear-shear, galaxy-galaxy, and galaxy-shear correlation functions from the Dark Energy Survey, and distance moduli measurements from Type Ia Supernovae. The tightest bounds we find are $\sum m_ν<0.43$ eV and $m_a<1.1$ eV, both at $95\%$ CL. Interestingly, these limits are still much stronger than those found on e.g. laboratory neutrino mass searches, reassessing the robustness of the extraction of thermal relic properties via cosmological observations. In addition, when considering lensing-only data, the significance of the Hubble constant tension is considerably reduced, while the clustering parameter $σ_8$ controversy is completely absent.

astro-ph.CO↗

arXiv2023

Model-independent reconstruction of the Interacting Dark Energy Kernel: Binned and Gaussian process

The cosmological dark sector remains an enigma, offering numerous possibilities for exploration. One particularly intriguing option is the (non-minimal) interaction scenario between dark matter and dark energy. In this paper, to investigate this scenario, we have implemented Binned and Gaussian model-independent reconstructions for the interaction kernel alongside the equation of state; while using data from BAOs, Pantheon+ and Cosmic Chronometers. In addition to the reconstruction process, we conducted a model selection to analyze how our methodology performed against the standard $Λ$CDM model. The results revealed a slight indication, of at least 1$σ$ confidence level, for some oscillatory dynamics in the interaction kernel and, as a by-product, also in the DE and DM. A consequence of this outcome is the possibility of a sign change in the direction of the energy transfer between DE and DM and a possible transition from a negative DE energy density in early-times to a positive one at late-times. While our reconstructions provided a better fit to the data compared to the standard model, the Bayesian Evidence showed an intrinsic penalization due to the extra degrees of freedom. Nevertheless these reconstructions could be used as a basis for other physical models with lower complexity but similar behavior.

astro-ph.CO↗

arXiv2023

New insights on $ν$-DM Interactions

We revisit the possibility of using cosmological observations to constrain models that involve interactions between neutrinos and dark matter. We show that small-scale measurements of the cosmic microwave background with a few per cent accuracy are critical to uncover unique signatures from models with tiny couplings that would require a much higher sensitivity at lower multipoles, such as those probed by the Planck satellite. We analyze the high-multipole data released by the Atacama Cosmology Telescope, both independently and in combination with Planck and Baryon Acoustic Oscillation measurements, finding a compelling preference for a non-vanishing coupling, $\log_{10}u_{ν\textrm{DM}}=-5.20^{+1.2}_{-0.74}$ at 68% CL. This aligns with other CMB-independent probes, such as Lyman-$α$. We illustrate how this coupling could be accounted for in the presence of dark matter interactions with a sterile neutrino.

astro-ph.CO↗

arXiv2023

Impact of the damping tail on neutrino mass constraints

Model-independent mass limits assess the robustness of current cosmological measurements of the neutrino mass scale. Consistency between high-multipole and low-multiple Cosmic Microwave Background observations measuring such scale further valuate the constraining power of present data. We derive here up-to-date limits on neutrino masses and abundances exploiting either the Data Release 4 of the Atacama Cosmology Telescope (ACT) or the South Pole Telescope polarization measurements from SPT-3G, envisaging different non-minimal background cosmologies and marginalizing over them. By combining these high-$\ell$ observations with Supernova Ia, Baryon Acoustic Oscillations (BAO), Redshift Space Distortions (RSD) and a prior on the reionization optical depth from WMAP data, we find that the marginalized bounds are competitive with those from Planck analyses. We obtain $\sum m_ν<0.139$ eV and $N_{\textrm{eff}}= 2.82\pm 0.25$ in a dark energy quintessence scenario, both at $95\%$ CL. These limits translate into $\sum m_ν<0.20$ eV and $N_{\textrm{eff}}= 2.79^{+0.30}_{-0.28}$ after marginalizing over a plethora of well-motivated fiducial models. Our findings reassess both the strength and the reliability of cosmological neutrino mass constraints.

astro-ph.CO↗

arXiv2023

Inflationary Potential as seen from Different Angles: Model Compatibility from Multiple CMB Missions

The cosmic microwave background (CMB) temperature and polarization anisotropies, as observed by independent astronomical missions such as WMAP, Planck, and most recently the Atacama Cosmology Telescope and the South Pole Telescope have played a vital role in accurately constraining cosmological theories and models, establishing cosmic inflation as the most widely accepted theory for describing the physics of the early Universe. However, the absence of a definitive detection of B-mode polarization and the emerging discrepancies among different CMB experiments present a challenge in determining which inflationary models best explain the observed data. In this work, we further explore this difficulty and conduct a case study by analyzing four well-known inflationary potentials in light of the latest CMB temperature and polarization anisotropy measurements and lensing data released by the Planck satellite and the Atacama Cosmology Telescope. Additionally, we incorporate B-modes polarization data from the BICEP/Keck Collaboration, as well as Baryon Acoustic Oscillations and Redshift Space Distortions measurements from BOSS DR12 and eBOSS DR16. We show that the most typical models such as Starobinsky and $α$-attractors are in disagreement with the Atacama Cosmology Telescope small-scale CMB measurements, particularly when combined with B-modes polarization data. On the other hand, these potentials are in perfect agreement with the Planck measurements at larger angular scales. This dichotomy makes it challenging to identify a single model or a group of models that can be universally considered as the preferred choice based on all available CMB observations.

astro-ph.CO↗

arXiv2023

Extended Analysis of Neutrino-Dark Matter Interactions with Small-Scale CMB Experiments

We explore an extension of the standard $Λ$CDM model by including an interaction between neutrinos and dark matter, and making use of the ground based telescope data of the Cosmic Microwave Background (CMB) from the Atacama Cosmology Telescope (ACT). An indication for a non-zero coupling between dark matter and neutrinos (both assuming a temperature independent and $T^2$ dependent cross-section) is obtained at the 1$σ$ level coming from the ACT CMB data alone and when combined with the Planck CMB and Baryon Acoustic Oscillations (BAO) measurements. This result is confirmed by both fixing the effective number of relativistic degrees of freedom in the early Universe to the Standard Model value of $N_{\rm eff}=3.044$, and allowing $N_{\rm eff}$ to be a free cosmological parameter. Furthermore, when performing a Bayesian model comparison, the interacting $ν$DM (+$N_{\rm eff}$) scenario is mostly preferred over a baseline $Λ$CDM (+$N_{\rm eff}$) cosmology. The preferred value is then used as a benchmark and the potential implications of dark matter's interaction with a sterile neutrino are discussed.

astro-ph.CO↗

arXiv2023

$Λ_{\rm s}$CDM model: A promising scenario for alleviation of cosmological tensions

We present a comprehensive analysis of the $Λ_{\rm s}$CDM model, which explores the recent conjecture suggesting a rapid transition of the Universe from anti-de Sitter vacua to de Sitter vacua (viz., the cosmological constant switches sign from negative to positive) at redshift ${z_\dagger\sim 2}$, inspired by the graduated dark energy (gDE) model. Our analysis shows that, predicting $z_\dagger\approx1.7$, $Λ_{\rm s}$CDM simultaneously addresses the major cosmological tensions of the standard $Λ$CDM model, viz., the Hubble constant $H_0$, the Type Ia Supernovae absolute magnitude $M_{\rm B}$, and the growth parameter $S_8$ tensions, along with other less significant tensions such as the BAO Lyman-$α$ discrepancy.

astro-ph.CO↗

arXiv2023

A Consistent View of Interacting Dark Energy from Multiple CMB Probes

We analyze a cosmological model featuring an interaction between dark energy and dark matter in light of the measurements of the Cosmic Microwave Background released by three independent experiments: the most recent data by the Planck satellite and the Atacama Cosmology Telescope, and WMAP (9-year data). We show that different combinations of the datasets provide similar results, always favoring an interacting dark sector with a $95\%$~CL significance in the majority of the cases. Remarkably, such a preference remains consistent when cross-checked through independent probes, while always yielding a value of the expansion rate $H_0$ consistent with the local distance ladder measurements. We investigate the source of this preference by scrutinizing the angular power spectra of temperature and polarization anisotropies as measured by different experiments.

astro-ph.CO↗

arXiv2023

IWDM: The fate of an interacting non-cold dark matter $-$ vacuum scenario

In most cosmological models, the equation of state of the dark matter is assumed to be zero, which means that the dark matter is pressure-less or cold. While this hypothesis is based on the abundance of cold dark matter in the universe, however, there is no compelling reason to assume that the equation of state of dark matter is exactly zero. A more general approach would be to allow for a range of values for the dark matter equation of state and use the observational data to determine which values are most likely. With the increasing accuracy of experimental data, we have chosen to explore the possibility of interacting non-cold dark matter $-$ vacuum scenario, where the equation of state of the dark matter is constant but can take different values within a specific range. Using the Cosmic Microwave Background (CMB) anisotropies and the CMB lensing reconstruction from the Planck legacy release, plus other non-CMB measurements, namely, the baryon acoustic oscillations distance measurements, and the Pantheon catalogue from Type Ia Supernovae, we have analyzed this scenario and found that a non-zero value for the dark matter equation of state is preferred with a confidence level of over 68\%. While this is not significant by itself, however, it does suggest that investigating the possibility of non-cold dark matter in the universe is worth exploring further to gain a better understanding of the nature of dark matter.

astro-ph.CO↗

arXiv2023

Exploring the $H_0$ tension and the evidence of dark sector interaction from 2D BAO measurements

We explore observational constraints on a cosmological model with an interaction between dark energy (DE) and dark matter (DM), using a compilation of 15 measurements of the 2D BAO (i.e., transversal) scale in combination with Planck-CMB data, to explore the parametric space of a class of interacting DE models. We find that 2D BAO measurements can generate different observational constraints compared to the traditional approach of studying the matter clustering in the 3D BAO measurements. Contrary to the observations for the $Λ$CDM and IDE models when analyzed with Planck-CMB + 3D BAO data, we note that Planck-CMB + 2D BAO data favor high values of the Hubble constant $H_0$. From the joint analysis with Planck-CMB + 2D BAO + Gaussian prior on $H_0$, we find $H_0 = 73.4 \pm 0.88$ km/s/Mpc. We conclude that the $H_0$ tension is solved in the IDE model with strong statistical evidence (more than 3$σ$) for the IDE cosmologies.

astro-ph.CO↗

arXiv2023

A novel model-marginalized cosmological bound on the QCD axion mass

We present model-marginalized limits on mixed hot dark matter scenarios, which consider both thermal neutrinos and thermal QCD axions. A novel aspect of our analyses is the inclusion of small-scale Cosmic Microwave Background (CMB) observations from the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT), together with those from the Planck satellite and Baryon Acoustic Oscillation (BAO) data. After marginalizing over a number of well-motivated non-minimal background cosmologies, the tightest $95\%$ CL upper bound we obtain is $0.21$ eV, both for $\sum m_ν$ and $m_{\rm a}$, from the combination of ACT, Planck and BAO measurements. Restricting the analyses to the standard $Λ$CDM picture, we find $\sum m_ν<0.16$ eV and $m_{\rm a}<0.18$ eV, both at $95\%$ CL. Interestingly, the best background cosmology is never found within the minimal $Λ$CDM plus hot relics, regardless of the data sets exploited in the analyses. The combination of Planck with either BAO, SPT or ACT prefers a universe with a non-zero value of the running in the primordial power spectrum with strong evidence. Small-scale CMB probes, both alone and combined with BAO, either prefer, with substantial evidence, non-flat universes (as in the case of SPT) or a model with a time varying dark energy component (as in the case of ACT).

astro-ph.CO↗

arXiv2023

Modified Gravity and Cosmology: An Update by the CANTATA Network

General Relativity and the $Λ$CDM framework are currently the standard lore and constitute the concordance paradigm. Nevertheless, long-standing open theoretical issues, as well as possible new observational ones arising from the explosive development of cosmology the last two decades, offer the motivation and lead a large amount of research to be devoted in constructing various extensions and modifications. All extended theories and scenarios are first examined under the light of theoretical consistency, and then are applied to various geometrical backgrounds, such as the cosmological and the spherical symmetric ones. Their predictions at both the background and perturbation levels, and concerning cosmology at early, intermediate and late times, are then confronted with the huge amount of observational data that astrophysics and cosmology are able to offer recently. Theories, scenarios and models that successfully and efficiently pass the above steps are classified as viable and are candidates for the description of Nature. This work is a Review of the recent developments in the fields of gravity and cosmology, presenting the state of the art, high-lighting the open problems, and outlining the directions of future research. Its realization was performed in the framework of the COST European Action ``Cosmology and Astrophysics Network for Theoretical Advances and Training Actions''.

gr-qc↗