arXiv subjects

Simony Santos da Costa

Publications and source records attributed to Simony Santos da Costa.

11 recordsLinked to original sources

arXiv2026

Effective Neutrino Mass and Apparent Phantom Crossing

Recent cosmological constraints on the sum of neutrino masses have reached, and in some analyses fallen below, the minimum value implied by the normal mass ordering, suggesting a possible tension with neutrino-oscillation measurements. We investigate whether this discrepancy can be alleviated in a mass-varying-neutrino (MaVaN) cosmology in which a canonical pseudo-Nambu-Goldstone boson (pNGB) drives late-time cosmic acceleration and controls the masses of massive neutrinos through an exponential coupling. Using current cosmic microwave background, baryon acoustic oscillation, and type Ia supernova data, we reconstruct the neutrino-mass evolution and show that the cosmologically inferred effective neutrino mass can fall below the present-day normal-ordering floor while remaining consistent with oscillation constraints. The same interaction produces a distinctive late-time signature, with 96% of the posterior expansion histories exhibiting a crossing of the apparent phantom divide, $w_{\rm app}=-1$, at $z_{\rm cross}=0.90^{+0.28}_{-0.13}$ at 68% C.L. The underlying scalar field nevertheless remains canonical, with $w_ϕ\geq -1$. Our results therefore show that neutrino mass variation can simultaneously alleviate the apparent neutrino-mass tension and generate the phantom-crossing behavior favored by current cosmological data, without introducing a phantom field or violating the null energy condition.

astro-ph.CO↗

arXiv2026

Cosmological Constraints on Neutrino Masses in Quintessential Inflation

Quintessential inflation provides a unified description of the early and late accelerated phases of the Universe, linking the inflationary epoch to the present-day dark energy-dominated era through a single scalar degree of freedom. In this work, we explore the implications of this unification for cosmological constraints on the sum of neutrino masses. Focusing on the $α$-attractor scenario, we implement the model in a modified version of the Boltzmann solver CLASS to compute the relevant cosmological observables and perform a Bayesian parameter estimation analysis using data from the cosmic microwave background (CMB), baryon acoustic oscillations (BAOs), and Type Ia supernovae. The model naturally breaks the degeneracy between the dark energy equation of state and the total neutrino mass, yielding tight upper bounds of $\sum m_ν< 0.067$ eV for flat spatial geometry and $\sum m_ν< 0.116$ eV when curvature is included. We also provide forecasts for future probes, showing that the Simons Observatory, LiteBIRD, and Euclid configurations may reduce the uncertainty on $\sum m_ν$ by $\approx 9\%$, while the precision on the quintessential parameter $α_{QI}$ is improved by $\approx 72\%$. These results highlight the importance of consistently accounting for neutrino mass when assessing the viability of extensions to the standard cosmological model.

astro-ph.CO↗

arXiv2025

Neutrino cosmology after DESI: tightest mass upper limits, preference for the normal ordering, and tension with terrestrial observations

The recent DESI Baryon Acoustic Oscillation measurements have led to tight upper limits on the neutrino mass sum, potentially in tension with oscillation constraints requiring $\sum m_ν \gtrsim 0.06\,{\text{eV}}$. Under the physically motivated assumption of positive $\sum m_ν$, we study the extent to which these limits are tightened by adding other available cosmological probes, and robustly quantify the preference for the normal mass ordering over the inverted one, as well as the tension between cosmological and terrestrial data. Combining DESI data with Cosmic Microwave Background measurements and several late-time background probes, the tightest $2σ$ limit we find without including a local $H_0$ prior is $\sum m_ν<0.05\,{\text{eV}}$. This leads to a strong preference for the normal ordering, with Bayes factor relative to the inverted one of $46.5$. Depending on the dataset combination and tension metric adopted, we quantify the tension between cosmological and terrestrial observations as ranging between $2.5σ$ and $5σ$. These results are strenghtened when allowing for a time-varying dark energy component with equation of state lying in the physically motivated non-phantom regime, $w(z) \geq -1$, highlighting an interesting synergy between the nature of dark energy and laboratory probes of the mass ordering. If these tensions persist and cannot be attributed to systematics, either or both standard neutrino (particle) physics or the underlying cosmological model will have to be questioned.

astro-ph.CO↗

arXiv2024

Impact of DESI BAO Data on Inflationary Parameters: stability against late-time new physics

In this work, I investigate the impact of Dark Energy Spectroscopic Instrument (DESI) Baryonic Acoustic Oscillations (BAO) data on cosmological parameters, focusing on the inflationary spectral index $n_s$, the amplitude of scalar perturbations $A_s$, and the matter density parameter $ω_m$. By examining different models of late-time new physics, the inflationary parameters were revealed to be stable when compared with the baseline dataset that used the earlier BAO data from the SDSS collaboration. When combined with Cosmic Microwave Background (CMB) and type Ia supernovae (SNeIa), DESI BAO data leads to a slight reduction in $ω_m$ (less than 2\%) and modest changes in $A_s$ and $n_s$, if compared with the same combination but using SDSS BAO data instead, suggesting a subtle shift in matter clustering. These effects may be attributed to a higher expansion rate from dynamical dark energy, changes in the recombination period, or modifications to the matter-radiation equality time. Further analyses of models with dynamical dark energy and free curvature show a consistent trend of reduced $ω_m$, accompanied by slight increases in both $n_s$ and $H_0$. The results emphasize the importance of the DESI BAO data in refining cosmological parameter estimates and highlight the stability of inflationary parameters across different late-time cosmological models.

astro-ph.CO↗

arXiv2024

Nonparametric late-time expansion history reconstruction and implications for the Hubble tension in light of recent DESI and type Ia supernovae data

We nonparametrically reconstruct the late-time expansion history in light of the latest Baryon Acoustic Oscillation (BAO) measurements from DESI combined with various Type Ia Supernovae (SNeIa) catalogs, using interpolation through piece-wise natural cubic splines, and a reconstruction procedure based on Gaussian Processes (GPs). Applied to DESI BAO and PantheonPlus SNeIa data, both methods indicate that deviations from a reference $Λ$CDM model in the $z \lesssim 2$ unnormalized expansion rate $E(z)$ are constrained to be $\lesssim 10\%$, but also consistently identify two features in $E(z)$: a bump at $z \sim 0.5$, and a depression at $z \sim 0.9$, which cannot be simultaneously captured by a $w_0w_a$CDM fit. These features, which are stable against assumptions regarding spatial curvature, interpolation knots, and GP kernel, disappear if one adopts the older SDSS BAO measurements in place of DESI, and decrease in significance when replacing the PantheonPlus catalog with the Union3 and DESY5 ones. We infer $c/(r_dH_0)=29.90 \pm 0.33$, with $r_d$ the sound horizon at baryon drag and $H_0$ the Hubble constant. Breaking the $r_d$-$H_0$ degeneracy with the SH0ES prior on $H_0$, the significance of the tension between our nonparametric determination of $r_d=136.20^{+2.20}_{-2.40}\,{\text{Mpc}}$ and the \textit{Planck} $Λ$CDM-based determination is at the $5σ$ level, slightly lower than the $6σ$ obtained when adopting the older SDSS dataset in place of DESI. This indicates the persistence at very high significance of the ``sound horizon tension'', reinforcing the need for pre-recombination new physics. If substantiated in forthcoming data releases, our results tentatively point to oscillatory/nonmonotonic features in the shape of the expansion rate at $z \lesssim 2$, of potential interest for dark energy model-building.

astro-ph.CO↗

arXiv2024

Multidimensionality of the Hubble tension: the roles of $Ω_m$ and $ω_c$

The Hubble tension is inherently multidimensional, and bears important implications for parameters beyond $H_0$. We discuss the key role of the matter density parameter $Ω_m$ and the physical cold dark matter density $ω_c$. We argue that once $Ω_m$ and the physical baryon density $ω_b$ are calibrated, through Baryon Acoustic Oscillations (BAO) and/or Type Ia Supernovae (SNeIa) for $Ω_m$, and via Big Bang Nucleosynthesis for $ω_b$, any model raising $H_0$ requires raising $ω_c$ and, under minimal assumptions, also the clustering parameter $S_8$. We explicitly verify that this behaviour holds when analyzing recent BAO and SNeIa data. We argue that a calibration of $Ω_m$ as reliable and model-independent as possible should be a priority in the Hubble tension discussion, and an interesting possibility in this sense could be represented by galaxy cluster gas mass fraction measurements.

astro-ph.CO↗

arXiv2024

Gauge invariant quantum backreaction in U(1) axion inflation

We evaluate the quantum backreaction due to a gauge field coupled to a pseudo-scalar field driving a slow-roll inflationary stage, the so-called axion inflation. The backreaction is evaluated for the first time using a gauge invariant approach, going to second order in perturbation theory, and taking into consideration inflaton fluctuations as well as scalar perturbations of the metric. Within our gauge-invariant, but observer-dependent approach, we naturally consider as physical observers the ones comoving with the inflaton field. Considering the effective expansion rate consequent to the gauge field's backreaction, we observe that the backreaction effect becomes significant quite rapidly, moving the system out of the perturbative regime and into what is often referred to as the strong backreaction regime. This behavior also applies to the parameter that dictates the production of the gauge fields. The space-time backreaction is mainly due to the helicity contribution within the region of validity of the perturbative regime. As a final result, we see that the evaluated backreaction goes in the direction of prolonging the inflationary period more compared to the scenarios previously studied.

gr-qc↗

arXiv2022

Constraining non-minimally coupled $β$-exponential inflation with CMB data

The $β$-exponential inflation is driven by a class of primordial potentials, derived in the framework of braneworld scenarios, that generalizes the well-known power law inflation. In this paper we update previous constraints on the minimal coupled $β$-exponential model [1] and extend the results also deriving the equations for the non-minimal coupled scenario. The predictions of both models are tested in light of the latest temperature and polarization maps of the Cosmic Microwave Background and clustering data. We also compare the predictions of these models with the standard $Λ$CDM cosmology using the Deviance Information Criterion (DIC), and find that the observational data show a moderate preference for the non-minimally coupled $β$-exponential inflationary model.

astro-ph.CO↗

arXiv2018

Observational constraints on Gauss-Bonnet cosmology

We analyze a fully geometric approach to dark energy in the framework of $F(R,{\cal G})$ theories of gravity, where $R$ is the Ricci curvature scalar and ${\cal G}$ is the Gauss-Bonnet topological invariant. The latter invariant naturally exhausts, together with $R$, the whole curvature content related to curvature invariants coming from the Riemann tensor. In particular, we study a class of $F(R, {\cal G})$ models with power law solutions and find that, depending on the value of the geometrical parameter, a shift in the anisotropy peaks position of the temperature power spectrum is produced, as well as an increasing in the matter power spectrum amplitude. This fact could be extremely relevant to fix the form of the $F(R, {\cal G})$ model. We also perform a MCMC analysis using both Cosmic Microwave Background data by the Planck (2015) release and the Joint Light-Curve Analysis of the SNLS-SDSS collaborative effort, combined with the current local measurements of the Hubble value, $H_0$, and galaxy data from the Sloan Digital Sky Survey (BOSS CMASS DR11). We show that such a model can describe the CMB data with slightly high $H_0$ values, and the prediction on the amplitude matter spectrum value is proved to be in accordance with the observed matter distribution of the universe. At the same time, the value constrained for the geometric parameter implies a density evolution of such a components that is growing with time.

gr-qc↗

arXiv2018

Dynamical analysis on $f(R,\mathcal{G})$ cosmology

We use a dynamical system approach to study the cosmological viability of $f(R,\mathcal{G})$ gravity theories. The method consists of formulating the evolution equations as an autonomous system of ODEs, using suitable variables. The formalism is applied to a class of models in which $f(R,\mathcal{G})\propto R^{n}\mathcal{G}^{1-n}$ and its solutions and corresponding stability are analysed in detail. New accelerating solutions that can be attractors in the phase space are found. We also find that this class of models does not exhibit a matter-dominated epoch, a solution which is inconsistent with current cosmological observations.

gr-qc↗

arXiv2017

A Bayesian analysis of inflationary primordial spectrum models using Planck data

The current available CMB data show an anomalously low value of the CMB temperature fluctuations at large angular scales (l < 40). This lack of power is not explained by the minimal LCDM model, and one of the possible mechanisms explored in the literature to address this problem is the presence of features in the primordial power spectrum (PPS) motivated by the early universe physics. In this paper, we analyse a set of cutoff inflationary PPS models using a Bayesian model comparison approach in light of the latest Cosmic Microwave Background (CMB) data from the Planck Collaboration. Our results show that the standard power-law parameterisation is preferred over all models considered in the analysis, which motivates the search for alternative explanations for the observed lack of power in the CMB anisotropy spectrum.

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