arXiv subjects

Enrico Specogna

Publications and source records attributed to Enrico Specogna.

7 recordsLinked to original sources

arXiv2025

Slow-rolling down the curvature: a reassessment of the Planck constraints on $\phi^2$ inflation in a closed universe

We revisit the Cosmic Microwave Background (CMB) constraints on the spatial curvature of the Universe, assessing how they change when the curvature parameter and the primordial inflationary scalar spectrum are treated consistently within theoretically motivated frameworks. Instead of relying on the phenomenological parametrisation commonly used to capture curvature effects at the largest scales, we present a case study based on closed quadratic inflation, where the primordial spectrum is derived in full generality and in a gauge-invariant manner. Within this framework, we analyze both the $\texttt{plik}$ PR3 and $\texttt{CamSpec}$ PR4 Planck CMB likelihoods and find that the constraints on $\Omega_{\mathcal{K}}$ shift towards spatial flatness. In $\texttt{plik}$ the preference for $\Omega_{\mathcal{K}}<0$ decreases from $\gtrsim 3.5\sigma$ to $\sim 2.5\sigma$, while in $\texttt{CamSpec}$ it reduces to $\sim 2\sigma$. At large angular scales ($\ell < 10$), our model explains the low-$\ell$ power suppression anomaly, notably improving the fit to the quadrupole. However, the reduced preference for highly negative values of $\Omega_{\mathcal{K}}$ only partially accounts for the lensing anomaly at high multipoles, worsening the fit to the $\texttt{plik}$ spectrum at small scales. By contrast, in the $\texttt{CamSpec}$ PR4 spectrum, where the lensing anomaly is less pronounced, the model yields an overall improvement. Our analysis highlights a key conceptual point: closed-inflation models tie the curvature parameter to the inflationary dynamics and the primordial spectrum, enforcing consistency conditions that do not necessarily allow for the large deviations from flatness seen in phenomenological parametrisations. In the case of quadratic inflation, these restrictions reduce the apparent evidence for negative curvature reported by earlier analyses, while allowing for a mildly closed geometry.

astro-ph.CO↗

arXiv2025

Neutrino mass tension or suppressed growth rate of matter perturbations?

Assuming a minimal $\Lambda$CDM cosmology with three massive neutrinos, the joint analysis of Planck cosmic microwave background data, DESI baryon acoustic oscillations, and distance moduli measurements of Type Ia supernovae from the Pantheon+ sample sets an upper bound on the total neutrino mass, $\sum m_\nu \lesssim 0.06$-$0.07$ eV, that lies barely above the lower limit from oscillation experiments. These constraints are mainly driven by mild differences in the inferred values of the matter density parameter across different probes that can be alleviated by introducing additional background-level degrees of freedom (e.g., by dynamical dark energy models). However, in this work we explore an alternative possibility. Since both $\Omega_\mathrm{m}$ and massive neutrinos critically influence the growth of cosmic structures, we test whether the neutrino mass tension may originate from the way matter clusters, rather than from a breakdown of the $\Lambda$CDM expansion history. To this end, we introduce the growth index $\gamma$, which characterizes the rate at which matter perturbations grow. Deviations from the standard $\Lambda$CDM value ($\gamma \simeq 0.55$) can capture a broad class of models, including non-minimal dark sector physics and modified gravity. We show that allowing $\gamma$ to vary significantly relaxes the neutrino mass bounds to $\sum m_\nu \lesssim 0.13$-$0.2$ eV, removing any tension with terrestrial constraints without altering the inferred value of $\Omega_\mathrm{m}$. However, this comes at the cost of departing from standard growth predictions: to have $\sum m_\nu \gtrsim 0.06$ eV one needs $\gamma > 0.55$, and we find a consistent preference for $\gamma > 0.55$ at the level of $\sim 2\sigma$. This preference increases to $\sim 2.5$-$3\sigma$ when a physically motivated prior $\sum m_\nu \ge 0.06$ eV from oscillation experiments is imposed.

astro-ph.CO↗

arXiv2025

Updated Constraints on Omnipotent Dark Energy: A Comprehensive Analysis with CMB and BAO Data

In this work, we present updated observational constraints on the parameter space of the DMS20 dark energy model, a member of the omnipotent dark energy (ODE) class. Our analysis combines multiple CMB datasets - including measurements from the Planck satellite (PL18), the South Pole Telescope (SPT), and the Wilkinson Microwave Anisotropy Probe (WMAP) - with Type Ia supernova data from the Pantheon$+$ catalog (PP), and baryon acoustic oscillation (BAO) measurements from the DESI and SDSS surveys. We find that certain data combinations, such as SPT+WMAP+BAO and PL18+BAO, can reduce the significance of the $H_0$ tension below $1\sigma$, but with considerably large uncertainties. However, the inclusion of PP data restores the tension in $H_0$. To provide a comprehensive view of the ODE phenomenology, we also investigate the evolution of its energy density, emphasizing its dynamical behavior at low redshifts. Our results generically exhibit multiple phantom divide line crossings in a single expansion history; if confirmed, this points beyond the simplest minimally coupled canonical single-field quintessence/phantom descriptions and motivates more general dark-sector realizations.

gr-qc↗

arXiv2024

Planck-PR4 anisotropy spectra show (better) consistency with General Relativity

We present the results from a series of analyses on two parametric tests of gravity that modify the growth of linear, sub-horizon matter perturbations in the $\Lambda$CDM model. The first test, known as the $(\mu,\Sigma)$ framework, modifies the Poisson and lensing equations from General Relativity (GR). The second test introduces the growth index $\gamma$, which directly affects the time evolution of matter density perturbations. Our study is motivated by results from the analysis of the Planck-PR3 2018 spectra, which indicate a preference for $\Sigma_0 \neq 0$ and $\gamma_0 > 0.55$, both of which deviate from the $\Lambda$CDM predictions at a significance level of $\sim 2.5\sigma$. To clarify the nature of these anomalous results and understand how the lensing anomaly fits into the picture, we analyze the most recent Planck-PR4 spectra extracted from the updated \texttt{NPIPE} maps. Overall, the Planck-PR4 data show better consistency with GR. The updated likelihood \texttt{Camspec} provides constraints on $\Sigma_0$ and $\gamma_0$ that are consistent with GR within $1.5\sigma$ and $2\sigma$, respectively. The updated likelihoods \texttt{HiLLiPoP} and \texttt{LoLLiPoP} show even closer agreement, with all parameter values consistent with a $\Lambda$CDM cosmology within $1\sigma$. This enhanced consistency is closely correlated with the lensing anomaly. Across the different likelihoods, the tendency of $\Sigma_0$ and $\gamma_0$ to drift towards non-standard values matches the observed preference for $A_L > 1$, both of which are significantly reduced or disappear within the Planck-PR4 data.

astro-ph.CO↗

arXiv2024

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

Due to universality and attractor properties, $\alpha$-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 $\alpha$, models inspired by supergravity where $\alpha$ takes on values up to $\alpha=7/3$, and Starobinsky inflation ($\alpha=1$). 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 $\alpha$-attractors lead to an improved fit over $\Lambda$CDM. For the large-scale CMB measurements, $\alpha\gtrsim2$ models can provide equally good fits as $\Lambda$CDM.

astro-ph.CO↗

arXiv2023

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 $\Lambda$CDM, whose actual or effective DE density is omnipotent, in alleviating the observational discordance within $\Lambda$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

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

In this study we investigate the growth index $\gamma_L$, 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 $\Lambda$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 $\gamma_L$ with its $\Lambda$CDM value in both cases. Conversely, the alternative ground-based telescopes ACT and SPT consistently yield growth index values in agreement with $\gamma_L=0.55$. 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↗