arXiv subjects

Vasco Gennari

Publications and source records attributed to Vasco Gennari.

6 recordsLinked to original sources

arXiv2026

Spectral sirens cosmology from binary black holes populations with sharper mass features

Spectral-sirens inference enables the extraction of cosmological parameters from gravitational-wave data alone, without electromagnetic counterparts or galaxy catalogs. We introduce new parametric mass functions for the binary black hole population built as linear combination of truncated power-laws that capture significant structure across the mass spectrum. On analysing the latest gravitational-wave transient catalog, GWTC-4.0, we show that power-laws-only population models constrain the Hubble constant to $H_0 = 53.3^{+14.0}_{-10.8} ~\rm km \,s^{-1} \,Mpc^{-1}$ at $68\%$ confidence level. After probing the robustness of the results with respect to several modelling assumptions, we further test alternative cosmological models, establishing competitive constraints on modified gravitational-wave propagation, while bounds on the dark energy equation-of-state parameters remain uninformative. Projecting to the future O5 observing run with larger datasets at higher redshifts, we forecast substantial improvements in $H_0$ and modified propagation parameters. Our results highlight the strong interplay between the black hole mass distribution and inferred cosmology.

gr-qc↗

arXiv2026

Black hole spectroscopy: from theory to experiment

The "ringdown" radiation emitted by oscillating black holes has great scientific potential. By carefully predicting the frequencies and amplitudes of black hole quasinormal modes and comparing them with gravitational-wave data from compact binary mergers we can advance our understanding of the two-body problem in general relativity, verify the predictions of the theory in the regime of strong and dynamical gravitational fields, and search for physics beyond the Standard Model or new gravitational degrees of freedom. We summarize the state of the art in our understanding of black hole quasinormal modes in general relativity and modified gravity, their excitation, and the modeling of ringdown waveforms. We also review the status of LIGO-Virgo-KAGRA ringdown observations, data analysis techniques, and the bright prospects of the field in the era of LISA and next-generation ground-based gravitational-wave detectors.

gr-qc↗

arXiv2026

Emergent structure in the binary black hole mass distribution and implications for population-based cosmology

Gravitational waves provide a powerful probe of both the astrophysical processes driving black hole mergers and the dynamics of the Universe, but these measurements rely on accurately inferring the unknown underlying population. We perform an agnostic reconstruction of the primary mass distribution using B-splines, characterising the emergence of structure with increasing model complexity. Using the latest gravitational-wave transient catalog, GWTC-4.0, we identify multiple mass features and find evidence suggesting a logarithmic hierarchy in the population. We show that this structure directly impacts measurements of the Hubble constant, primarily through features at the population boundaries. Finally, we introduce an approach that isolates a subpopulation of low-mass events to mitigate modelling systematics, providing a promising path toward robust population-based cosmology with future datasets.

gr-qc↗

arXiv2025

Towards a few percent measurement of the Hubble constant with the current network of gravitational wave detectors without using electromagnetic information

Gravitational waves provide a novel and independent measurement of cosmological parameters, offering a promising avenue to address the Hubble tension alongside traditional electromagnetic observations. In the absence of electromagnetic counterparts or complete host galaxy catalogs, current measurements rely on population-based methods that statistically combine black hole merger events. Building on recent models that incorporate additional structure in the primary black hole mass distribution, using public data from the LIGO-Virgo-KAGRA (LVK) collaboration third observing run (O3), we obtain a 30% accuracy improvement on the measurement of the Hubble constant with respect to the result reported by LVK with the third GW transient catalog (GWTC-3). Employing a realistic simulation that includes full Bayesian single-event inference, we present forecasts for the upcoming LVK observational runs, O4 and O5. Using a three power-law mass model, we project a measurement of the Hubble constant with 20% accuracy at O4 sensitivity, improving to 2.7% accuracy at O5 sensitivity. Our findings demonstrate the potential for gravitational waves to provide a substantial contribution to solving the Hubble tension within the next decade of observations.

gr-qc↗

arXiv2025

Searching for additional structure and redshift evolution in the observed binary black hole population with a parametric time-dependent mass distribution

The population of the observed gravitational wave events encodes unique information on the formation and evolution of stellar-mass black holes, from the underlying astrophysical processes to the large-scale dynamics of the Universe. We use the ICAROGW analysis infrastructure to perform hierarchical Bayesian inference on the gravitational wave signals from the LIGO-Virgo-KAGRA third observing run, O3. Searching for additional structure and redshift evolution in the primary mass distribution, we explore the dependence of the mass spectrum reconstruction on different parametrizations and prior choices. For the stationary case, we find strong evidence (Bayes factor $B \simeq 180$) that the results obtained using a power-law model with a peak (Powerlaw-Gaussian)--the model preferred so far in the literature--are sensitive to prior bounds, affecting the resolvability of the $\sim 35 M_{\odot}$ peak. This behaviour is reproduced by simulated data, indicating a bimodal structure in the likelihood. Models with three mass features simultaneously capture a sharp $\sim 10M_{\odot}$ peak, a $\sim 35 M_{\odot}$ overdensity, and support for a $\sim 20 M_{\odot}$ overdensity preceded by a dip. Among these, a model with three power-law peaks (Powerlaw-Powerlaw-Powerlaw) is equally favored, in terms of evidence, over the Powerlaw-Gaussian model with wide priors. We find no statistical support for redshift evolution in the current data and provide constraints on the parameters governing this evolution, showing consistency with stationarity. We highlight possible limitations of the hierarchical Bayesian inference framework in reconstructing evolving features outside the detector horizon. Our work lays the foundations for a robust characterization of time-dependent population distributions, with significant implications for black hole astrophysics and gravitational wave cosmology.

gr-qc↗

arXiv2024

Searching for ringdown higher modes with a numerical relativity-informed post-merger model

Robust measurements of multiple black hole vibrational modes provide a unique opportunity to characterise gravity in extreme curvature and dynamical regimes, to better investigate the nature of compact objects and search for signs of new physics. We use a numerically-tuned quasicircular non-precessing ringdown model, $\texttt{TEOBPM}$, and the $\texttt{pyRing}$ analysis infrastructure to perform a time-domain spectroscopic analysis of the third catalog of transient gravitational-wave signals, GWTC-3, searching for higher angular modes. The $\texttt{TEOBPM}$ model effectively includes non-linearities in the early post-merger signal portion, and carries information about the progenitors parameters through time-dependent excitation amplitudes of the black hole quasinormal modes. Such a strategy allows us to accurately model the full post-merger emission, recovering higher signal-to-noise ratios compared to templates based on more agnostic superpositions of damped-sinusoids. We find weak evidence for the presence of $(l,m)=(3,3)$ [$(l,m)=(2,1)$] mode in several events, with the largest Bayes factor in favour of this mode being $\mathcal{B}\simeq 2.6$ [$\mathcal{B}\simeq 1.2$] within the peak time distribution support. For GW190521, we observe $\mathcal{B}\simeq 5.1$, but only for times outside the peak time support reconstructed using the highly accurate $\texttt{NRSur7dq4}$ model, indicating significant systematics affecting such putative detection. Allowing for deviations from general relativity under the assumption of the presence of two modes, we find tentative support for the Kerr "final state conjecture". Our work showcases a systematic methodology to robustly identify and characterise higher angular modes in ringdown-only signals, highlighting the significant impact of modelling assumptions and peak time uncertainty on spectroscopic measurements, at current signal-to-noise ratios.

gr-qc↗