arXiv subjects

Ana Lorenzo-Medina

Publications and source records attributed to Ana Lorenzo-Medina.

7 recordsLinked to original sources

arXiv2025

Seeking Spinning Subpopulations of Black Hole Binaries via Iterative Density Estimation

Attempts to understand the formation of binary black hole (BBH) systems detected via gravitational wave (GW) emission are affected by many unknowns and uncertainties, from both the observational and theoretical (astrophysical modelling) sides. Binary component spins have been proposed as a means to investigate formation channels, however obtaining clear inferences is challenging, given the apparently low magnitude of almost all merging BH spins and their high measurement uncertainties. Even for the effective aligned spin $χ_{\mathrm{eff}}$ which is more precisely measured than component spins, specific model assumptions have been required to identify any clear trends. Here, we reconstruct the joint component mass and $χ_{\mathrm{eff}}$ distribution of BBH mergers with minimal assumptions using the GWTC-3 catalog, using an iterative kernel density estimation (KDE)-based method. We reproduce some features seen in previous analyses, for instance a small but preferentially positive $χ_{\mathrm{eff}}$ for low-mass mergers; we also identify a possible subpopulation of higher-spin BBH with $|χ_{\mathrm{eff}}|$ up to $\sim\! 0.75$ for primary masses $m_1 \gtrsim 40\,M_\odot$, in addition to the bulk of the distribution with $|χ_{\mathrm{eff}}| \lesssim 0.2$. This finding is consistent with previous studies indicating a broader spin distribution at high mass, suggesting a distinct origin for the high-spin systems. We also identify a new potential trend of low-mass BBHs: the \emph{derivative} of $χ_{\mathrm{eff}}$ with respect to $m_1$ ($m_2$) is positive (negative) over the $10$--$15\,M_\odot$ range. This apparent structure may be related to} a previously reported anticorrelation between mass ratio and $χ_{\mathrm{eff}}$.

astro-ph.HE↗

arXiv2025

Identifying Proca-star mergers via consistent ultralight-boson mass estimates across gravitational-wave events

While black-hole and neutron-star mergers are the most plausible sources of current gravitational-wave observations, mergers of exotic compact objects may mimic these signals. Proca stars -- Bose-Einstein condensates of complex vector ultralight bosons -- have gained significant attention for their potential to replicate certain gravitational-wave events while yielding consistent estimates of the boson mass $μ_{B}$ forming the stars. Using a mixture model within a Bayesian framework, we demonstrate that consistent boson-mass estimates across events can be exploited to obtain conclusive evidence for the existence \cor{of} a number $n$ of Proca-star families characterized by respective boson masses $μ_{B}^{i}$, even if no individual event can be conclusively identified as such. Our method provides posterior distributions for $n$ and $μ_{B}^{i}$. Applying this framework to the high-mass events GW190521, GW190426\_190642 \cor{and} GW200220\_061928, we obtain a Bayes Factor ${\cal{B}}^{n=0}_{n=1}=2$ against the Proca-star hypothesis, primarily rooted in the limitation of current Proca-star merger \cor{signal models} to intrinsically weak head-on cases. We show that conclusive evidence $\log{\cal{B}}^{n=1}_{n=0} \geq 5$ could be achieved after 5 to 9 observations of similar event sets, at the $90\%$ credible level. Our framework provides a new way to detect exotic compact objects, somewhat using gravitational-wave detectors as particle detectors.

gr-qc↗

arXiv2025

Looking To The Horizon: Probing Evolution in the Black Hole Spectrum With Gravitational Wave Catalogs

The population of black holes observed via gravitational waves currently covers the local universe up to a redshift $z\lesssim 1$, for the most massive merging binaries, or $z\lesssim 0.25$ for low-mass BH binaries (BBH). Evolution of the BBH mass spectrum over cosmic time will be a significant probe of formation channels and environments. We demonstrate a reconstruction of the BBH merger rate, allowing for general dependence on binary masses and luminosity distance or redshift and accounting for selection effects, via iterative kernel density estimation (KDE) with optimized multidimensional bandwidths. Performing such reconstructions under a range of detailed assumptions, we see no significant evidence for the evolution of BBH masses with redshift, over the range where detected events are available. At most, possible trends towards increasing merger rate with redshift for primary masses $m_1\gtrsim 50\,M_\odot$, or towards decreasing merger rate with redshift for primary masses $m_1 \lesssim 40 M\odot$ may be supported. We compare these findings with previous investigations and caution against over-interpreting the current, sparse, data. Significantly upgraded detectors and/or facilities, and longer observing times, are required to harness any correlations of the BBH mass distribution with redshift.

gr-qc↗

arXiv2025

Self-consistent treatment of thermal effects in neutron-star post-mergers: observational implications for third-generation gravitational-wave detectors

We assess the impact of accurate, self-consistent modelling of thermal effects in neutron-star merger remnants in the context of third-generation gravitational-wave detectors. This is done through the usage, in Bayesian model selection experiments, of numerical-relativity simulations of binary neutron star (BNS) mergers modelled through: a) nuclear, finite-temperature (or ``tabulated'') equations of state (EoSs), and b) their simplifed piecewise (or ``hybrid'') representation. These cover four different EoSs, namely SLy4, DD2, HShen and LS220. Our analyses make direct use of the Newman-Penrose scalar $ψ_4$ outputted by numerical simulations. Considering a detector network formed by three Cosmic Explorers, we show that differences in the gravitational-wave emission predicted by the two models are detectable with a natural logarithmic Bayes Factor $\log{\cal{B}}\geq 5$ at average distances of $d_L \simeq 50$Mpc, reaching $d_L \simeq 100$Mpc for source inclinations $ι\leq 0.8$, regardless of the EoS. This impact is most pronounced for the HShen EoS. For low inclinations, only the DD2 EoS prevents the detectability of such modelling differences at $d_L \simeq 150$Mpc. Our results suggest that the usage a self-consistent treatment of thermal effects is crucial for third-generation gravitational wave detectors.

gr-qc↗

arXiv2025

A physically modelled selection function for compact binary mergers in the LIGO-Virgo O3 run and beyond

Despite the observation of nearly 100 compact binary coalescence (CBC) events up to the end of the Advanced gravitational-wave (GW) detectors' third observing run (O3), there remain fundamental open questions regarding their astrophysical formation mechanisms and environments. Population analysis should yield insights into these questions, but requires careful control of uncertainties and biases. GW observations have a strong selection bias: this is due first to the dependence of the signal amplitude on the source's (intrinsic and extrinsic) parameters, and second to the complicated nature of detector noise and of current detection methods. In this work, we introduce a new physically-motivated model of the sensitivity of GW searches for CBC events, aimed at enhancing the accuracy and efficiency of population reconstructions. In contrast to current methods which rely on re-weighting simulated signals (injections) via importance sampling, we model the probability of detection of binary black hole (BBH) mergers as a smooth, analytic function of source masses, orbit-aligned spins, and distance, fitted to accurately match injection results. The estimate can thus be used for population models whose signal distribution over parameter space differs significantly from the injection distribution. Our method has already been used in population studies such as reconstructing the BBH merger rate dependence on redshift.

gr-qc↗

arXiv2024

Numerical relativity surrogate models for exotic compact objects: the case of head-on mergers of equal-mass Proca stars

We present several high-accuracy surrogate models for gravitational-wave signals from equal-mass head-on mergers of Proca stars, computed through the Newman-Penrose scalar $ψ_4$. We also discuss the current state of the model extensions to mergers of Proca stars with different masses, and the particular challenges that these present. The models are divided in two main categories: two-stage and monolithic. In the two-stage models, a dimensional reduction algorithm is applied to embed the data in a reduced feature space, which is then interpolated in terms of the physical parameters. For the monolithic models, a single neural network is trained to predict the waveform from the input physical parameter. Our model displays mismatches below $10^{-3}$ with respect to the original numerical waveforms. Finally, we demonstrate the usage of our model in full Bayesian parameter inference through the accurate recovery of numerical relativity signals injected in zero-noise, together with the analysis of GW190521. For the latter, we observe excellent agreement with existing results that make use of full numerical relativity.

gr-qc↗

arXiv2024

Evidence for the evolution of black hole mass function with redshift

We investigate the joint primary mass, mass ratio, and redshift observed distribution of astrophysical black holes using the gravitational wave events detected by the LIGO-Virgo-KAGRA collaboration and included in the third gravitational wave transient catalogue. We reconstruct this distribution using Bayesian non-parametric methods, which are data-driven models able to infer arbitrary probability densities under minimal mathematical assumptions. We find evidence for the evolution with redshift of both the primary mass and mass ratio distribution: our analysis shows the presence of two distinct sub-populations in the primary mass - redshift plane, with the lighter population, $\lesssim$ 20 $M_\odot$, disappearing at higher redshifts, $z > 0.4$. The mass ratio distribution shows no support for symmetric binaries. The observed population of coalescing binary black holes evolves with look-back time, suggesting a trend in metallicity with redshift and/or the presence of multiple, redshift-dependent formation channels.

astro-ph.HE↗