arXiv subjects

Tommaso Moretti

Publications and source records attributed to Tommaso Moretti.

5 recordsLinked to original sources

arXiv2026

Can cosmic voids ease the Hubble tension? Local expansion in $w_0w_a$CDM

We investigate the effect of local cosmic voids on low-redshift measurements of the Hubble rate in flat $w_0w_a$CDM cosmologies. Using a hydrodynamical model for isolated spherical inverse top-hat underdensities, we compute the void-induced Hubble shift as a function of redshift, enclosed density contrast $\delta_{\rm E}$ and cosmological parameters. We find that the effect is mainly controlled by the matter sector, through $\delta_{\rm E}$ and $\Omega_{\rm m,0}$, while dynamical dark energy gives only subdominant late-time corrections. For a Planck-calibrated $\Lambda$CDM background, matching the SH0ES value requires a present-day void with $\delta_{\rm E}(z=0)\simeq -0.44$, substantially deeper than the KBC-like local underdensity. A KBC-like void lowers the SH0ES-Planck discrepancy to about $2\sigma$, but is not deep enough to fully reconcile the two measurements. Allowing for dynamical dark energy, including regions motivated by recent DES and DESI analyses, changes this result only at the percent level. We also show that the reported redshift dependence of locally inferred $H_0$ values can be represented phenomenologically by an effective enclosed matter profile. This reconstruction should be interpreted as a consistency test of local-structure effects rather than as explanation for an evolving background value of $H_0$. Overall, local underdensities can affect low-redshift Hubble-rate inferences, but they do not resolve the Hubble tension within the spherical void setup considered here.

astro-ph.CO↗

arXiv2026

Cosmic voids evolution in modified gravity via hydrodynamics

We present a hydrodynamical description of isolated spherical voids in modified gravity (MG), extending the standard General Relativity (GR) and dynamical dark energy treatment by encoding gravity modifications into effective couplings that enter the Euler and Poisson equations. This yields a compact non-linear evolution equation for the Eulerian density contrast, controlled by a time- and density-dependent effective gravitational strength, and provides a direct map between model functions and void observables. We apply the framework to the luminal Galileon class of models, where derivative self-interactions generate Vainshtein screening and might lead to a breakdown of the physical branch in sufficiently underdense regions. Exploiting this feature, we apply the void-informed viability requirement that translates into bounds on the theory parameter space and, equivalently, on the minimum attainable void depth as a function of redshift. For viable parameters of a concrete model, we quantify the impact of MG on isolated void evolution, the Lagrangian to Eulerian mapping, and the shell-crossing threshold. Relative to GR, we find a clear hierarchy of MG effects, with ${\cal O}(10\%)$ modifications in the gravitational couplings, percent-level shifts in the void density evolution, and sub-percent deviations in both the mapping and the shell-crossing thresholds. Moreover, within the adopted parametrization, we show analytically that voids always lie in an unscreened regime on the physical branch. Overall, the formalism provides a self-consistent route to predict void dynamics and consistency constraints in a broad class of MG models.

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arXiv2026

How deep can a cosmic void be? Voids-informed theoretical bounds in Galileon gravity

We establish a void-based consistency test for Galileon scalar-tensor theories. We show that the previously reported unphysical breakdown of the predicted Newtonian force in certain Galileon models is controlled by a single condition linking non-linear void dynamics to the cosmic expansion history. This connection yields a redshift-dependent upper bound on the allowed depth of voids and promotes this requirement to a new viability condition, complementary to standard stability criteria. As an example, we apply this void-based criterion to a linear parameterization in the scale factor constrained by theoretical and observational bounds; we find that $\sim 60\%$ of the parameter space is excluded, with most problematic models failing by $z\lesssim 10$. These results position cosmic voids as sharp, complementary and theory-informed filters for viable modified gravity, enabling more informed priors and parameter-space choices in future cosmological inference.

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arXiv2025

A spherical hydrodynamical model of cosmic voids in {\Lambda}CDM and beyond

Cosmic voids have emerged as powerful probes for cosmology, providing complementary information on the large-scale structure of the universe. We present the first application of a hydrodynamical framework to model the evolution of cosmic voids. This approach offers a physically intuitive characterization of void dynamics and can naturally be applied to non-standard cosmologies. We derive the cosmology-dependent mapping that relates the linear (Lagrangian) and fully non-linear (Eulerian) evolution of the matter density contrast, a central component for accurate theoretical modeling of void statistics. Furthermore, we present a new method for determining the shell-crossing epoch across arbitrary cosmological backgrounds, thereby extending previous treatments restricted to the Einstein-de Sitter universe. Motivated by recent DESI results hinting at dynamical dark energy, we investigate void evolution in $ w_0w_a$CDM cosmologies by varying $ w_0$ and $w_a$. We also consider the impact of varying the matter density parameter, $ \Omega_{\mathrm{m},0}$. We find that the evolution of isolated, spherically symmetric cosmic voids is most sensitive to $ \Omega_{\mathrm{m},0} $ and $ w_0 $, which can alter the non-linear density contrast by up to 20-30%. Variations in $w_a$ have a smaller impact, but may still lead to measurable effects. We also show that the cosmology-dependent mapping between linear and non-linear density contrasts may provide a sensitive probe of dynamical dark energy in precision void analyses.

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arXiv2024

Breaking parity: the case of the trispectrum from chiral scalar-tensor theories of gravity

Recently, possible hints of parity violation have been observed in the connected galaxy four-point correlation function. Although the true origin of the signal from the analysis has been debated, should they have a physical origin, they might point to primordial non-Gaussianity and would be evidence of new physics. In this work, we examine the single-field slow-roll model of inflation within chiral scalar-tensor theories of modified gravity. These theories, treated here as new Lorentz-breaking theories, extend the Chern-Simons one by including parity-violating operators containing first and second derivatives of the non-minimally coupled scalar (inflaton) field. This model is capable of imprinting parity-violating signatures in late-time observables, such as the galaxy four-point correlation function. We perform an analysis of the graviton-mediated scalar trispectrum of the gauge-invariant curvature perturbation $\zeta(t,\mathbf{x})$ using one of the parity-violating operators of these theories as a case study. We estimate that for a set of parameters of the theory it is possible to produce a signal-to-noise ratio for the parity-violating part of the trispectrum of order one without introducing modifications to the single-field slow-roll setup. Even if the signal found in the analysis turns out to be spurious or if no parity violation is ever detected in the galaxy four-point correlation function, our analysis can be used to constrain the free parameters of these theories.

astro-ph.CO↗