arXiv subjects

Alberto Vecchio

Publications and source records attributed to Alberto Vecchio.

At least 19 recordsLinked to original sources

arXiv2026

LISA and the LISA Science Team

LISA, the Laser Interferometer Space Antenna, due to launch mid-2035, is a large class space mission by the European Space Agency (ESA). In partnership with NASA and ESA-member states, ESA is on track to launch what is expected to be the first space-based gravitational wave detector. By hosting detectors in space, one gains access to a lower frequency band of gravitational wave sources and, with them, a plethora of new science. To maximise this scientific gain, ESA and NASA selected 20 scientists for the LISA Science Team to carry out and/or lead the necessary actions leading up to LISA's launch. We give a short overview and update of the LISA mission, its science objectives and related waveforms, as well as the work of the LISA Science Team as of April 2026.

astro-ph.IM↗

arXiv2025

In situ substrate birefringence characterization in gravitational wave detectors using a heterodyne polarimetry method

High-quality test mass substrates play essential roles in laser interferometric gravitational wave detectors. Inhomogeneous birefringence distribution in test mass substrates, however, can degrade the sensitivity of the detector by introducing the optical loss and disturbing the interferometer controls. In this paper, we present a heterodyne polarimetry method that enables in situ birefringence characterizations, hence diagnosing the gravitational wave interferometer. We experimentally demonstrate the proposed method with a tabletop setup. We also discuss its applicability to current and future gravitational wave detectors and the detectable limit.

physics.ins-det↗

arXiv2025

Global time-frequency search for stellar-mass binary black holes in LISA

We present a complete pipeline for detecting and characterizing gravitational waves (GWs) produced by the inspiral of stellar-mass binary black holes in data from the Laser Interferometer Space Antenna (LISA). The analysis framework relies on an efficient time-frequency implementation of an adaptive semi-coherent detection statistic, which we show to be robust against non-stationary noise and the presence of gaps of varying duration and cadence. The search is able to detect signals with coherent signal-to-noise ratios as low as $\approx 11-14$ over the full parameter space of binary black holes with spins aligned to the orbital angular momentum and orbital eccentricity $\le 0.01$ when deployed on the 2-year-long LISA Data Challenge Yorsh. The search can be run within a day using $\approx 40$ GPUs. The techniques presented here have wider applications in GW astronomy, in particular the search for extreme-mass-ratio inspirals in LISA data.

gr-qc↗

arXiv2025

Identifying galactic binary systems of neutron stars and black holes with LISA

The Laser Interferometer Space Antenna (LISA) will detect $\sim 100$ galactic binary systems comprised of black holes and neutron stars. Distinguishing these binaries from the $\sim 10^4$ double white dwarfs detectable by LISA will be challenging. In the absence of any other information, the inferred component masses can be used to classify the nature of these objects. However, short-period galactic binaries $\sim 10^7$--$10^3\,\mathrm{yr}$ from coalescence produce a quasi-monochromatic signal which carries little information about their masses. We generate synthetic LISA data sets containing gravitational waves from Galactic binary black holes, binary neutron stars and black hole-neutron stars drawn from an astrophysically realistic population produced through the isolated binary evolution channel. We use a Bayesian inference pipeline to explore the accuracy with which the component masses can be measured. LISA will be able to infer component masses for $\approx 10\% - 50\%$ of the detected systems by measuring the orbital eccentricity, periapse precession frequency, and gravitational-wave induced frequency derivative. Typical fractional mass errors are $\approx 1\%$--$100\%$ (depending on the specific value of the source parameters) enabling the classification of the constituent objects as black holes or neutron stars. For these binaries, LISA will also be able to determine their 3-dimensional position in the Milky Way. LISA detections of these double compact objects will provide new insights to their astrophysical formation processes, the Galactic population, and the Milky Way's star formation history. However, for a significant fraction of the LISA-detected binaries the nature of their constituent objects may remain unclear.

astro-ph.HE↗

arXiv2024

The NANOGrav 15 Yr Data Set: Removing Pulsars One by One from the Pulsar Timing Array

Evidence has emerged for a stochastic signal correlated among 67 pulsars within the 15-year pulsar-timing data set compiled by the NANOGrav collaboration. Similar signals have been found in data from the European, Indian, Parkes, and Chinese PTAs. This signal has been interpreted as indicative of the presence of a nanohertz stochastic gravitational wave background. To explore the internal consistency of this result we investigate how the recovered signal strength changes as we remove the pulsars one by one from the data set. We calculate the signal strength using the (noise-marginalized) optimal statistic, a frequentist metric designed to measure correlated excess power in the residuals of the arrival times of the radio pulses. We identify several features emerging from this analysis that were initially unexpected. The significance of these features, however, can only be assessed by comparing the real data to synthetic data sets. After conducting identical analyses on simulated data sets, we do not find anything inconsistent with the presence of a stochastic gravitational wave background in the NANOGrav 15-year data. The methodologies developed here can offer additional tools for application to future, more sensitive data sets. While this analysis provides an internal consistency check of the NANOGrav results, it does not eliminate the necessity for additional investigations that could identify potential systematics or uncover unmodeled physical phenomena in the data.

astro-ph.HE↗

arXiv2024

Premerger observation and characterization of massive black hole binaries

We demonstrate an end-to-end technique for observing and characterizing massive black hole binary signals before they merge with the LISA space-based gravitational-wave observatory. Our method uses a zero-latency whitening filter, originally designed for rapidly observing compact binary mergers in ground-based observatories, to be able to observe signals with no additional latency due to filter length. We show that with minimal computational cost, we are able to reliably observe signals as early as 14 days premerger as long as the signal has accrued a signal-to-noise ratio of at least 8 in the LISA data. We also demonstrate that this method can be used to characterize the source properties, providing early estimates of the source's merger time, chirp mass, and sky localization. Early observation and characterization of massive black holes is crucial to enable the possibility of rapid multimessenger observations, and to ensure that LISA can enter a protected operating period when the merger signal arrives.

hep-ex↗

arXiv2024

Which is which? Identification of the two compact objects in gravitational-wave binaries

Compact objects observed in gravitational-wave astronomy so far always come in pairs and never individually. Identifying the two components of a binary system is a delicate operation that is often taken for granted. The labeling procedure (i.e., which is object "1" and which is object "2") effectively acts as systematics, or, equivalently an unspecified prior, in gravitational-wave data inference. The common approach is to label the objects solely by their masses, on a sample-by-sample basis. We show that object identification can instead be tackled using the posterior distribution as a whole. We frame the problem in terms of constrained clustering -- a flavor of semi-supervised machine learning -- and find that unfolding the labeling systematics can significantly impact, and arguably improve, our interpretation of the data. In particular, the precision of black-hole spin measurements improves by up to 50%, multimodalities and tails tend to disappear, posteriors become closer to Gaussian distributions, and the identification of the nature of the object (i.e. black hole vs. neutron star) is facilitated. We estimate that about 10% of the LIGO/Virgo posterior samples are affected by this relabeling, i.e. they might have been attributed to the other compact object in the observed binaries.

gr-qc↗

arXiv2023

Precision tracking of massive black hole spin evolution with LISA

The Laser Interferometer Space Antenna (LISA) will play a vital role in constraining the origin and evolution of massive black holes throughout the Universe. In this study we use a waveform model (IMRPhenomXPHM) that includes both precession and higher multipoles, and full Bayesian inference to explore the accuracy to which LISA can constrain the binary parameters. We demonstrate that LISA will be able to track the evolution of the spins -- magnitude and orientation -- to percent accuracy, providing crucial information on the dynamics and evolution of massive black hole binaries and the galactic environment in which the merger takes place. Such accurate spin-tracking further allows LISA to measure the recoil velocity of the remnant black hole to better than $100\,\mathrm{km}\,\mathrm{s}^{-1}$ (90\% credibility) and its direction to a few degrees, which provides additional important astrophysical information on the post-merger association. Using a systematic suite of binaries, we showcase that the component masses will be measurable at the sub-percent level, the sky area can be constrained to within $\Delta \Omega_{90} \approx 0.01 \, \rm{deg}^2$, and the binary redshift to less than $0.01$.

gr-qc↗

arXiv2023

Implications of pulsar timing array observations for LISA detections of massive black hole binaries

Pulsar timing arrays (PTAs) and the Laser Interferometer Space Antenna (LISA) will open complementary observational windows on massive black-hole binaries (MBHBs), i.e., with masses in the range $\sim 10^6 - 10^{10}\,$ M$_{\odot}$. While PTAs may detect a stochastic gravitational-wave background from a population of MBHBs, during operation LISA will detect individual merging MBHBs. To demonstrate the profound interplay between LISA and PTAs, we estimate the number of MBHB mergers that one can expect to observe with LISA by extrapolating direct observational constraints on the MBHB merger rate inferred from PTA data. For this, we postulate that the common signal observed by PTAs (and consistent with the increased evidence recently reported) is an astrophysical background sourced by a single MBHB population. We then constrain the LISA detection rate, $\mathcal{R}$, in the mass-redshift space by combining our Bayesian-inferred merger rate with LISA's sensitivity to spin-aligned, inspiral-merger-ringdown waveforms. Using an astrophysically-informed formation model, we predict a 95$\%$ upper limit on the detection rate of $\mathcal{R} < 134\,{\rm yr}^{-1}$ for binaries with total masses in the range $10^7 - 10^8\,$ M$_{\odot}$. For higher masses, i.e., $>10^8\,$ M$_{\odot}$, we find $\mathcal{R} < 2\,(1)\,\mathrm{yr}^{-1}$ using an astrophysically-informed (agnostic) formation model, rising to $11\,(6)\,\mathrm{yr}^{-1}$ if the LISA sensitivity bandwidth extends down to $10^{-5}$ Hz. Forecasts of LISA science potential with PTA background measurements should improve as PTAs continue their search.

astro-ph.HE↗

arXiv2023

The International Pulsar Timing Array checklist for the detection of nanohertz gravitational waves

Pulsar timing arrays (PTAs) provide a way to detect gravitational waves at nanohertz frequencies. In this band, the most likely signals are stochastic, with a power spectrum that rises steeply at lower frequencies. Indeed, the observation of a common red noise process in pulsar-timing data suggests that the first credible detection of nanohertz-frequency gravitational waves could take place within the next few years. The detection process is complicated by the nature of the signals and the noise: the first observational claims will be statistical inferences drawn at the threshold of detectability. To demonstrate that gravitational waves are creating some of the noise in the pulsar-timing data sets, observations must exhibit the Hellings and Downs curve -- the angular correlation function associated with gravitational waves -- as well as demonstrating that there are no other reasonable explanations. To ensure that detection claims are credible, the International Pulsar Timing Array (IPTA) has a formal process to vet results prior to publication. This includes internal sharing of data and processing pipelines between different PTAs, enabling independent cross-checks and validation of results. To oversee and validate any detection claim, the IPTA has also created an eight-member Detection Committee (DC) which includes four independent external members. IPTA members will only publish their results after a formal review process has concluded. This document is the initial DC checklist, describing some of the conditions that should be fulfilled by a credible detection. At the present time none of the PTAs have a detection claim; therefore this document serves as a road map for the future.

astro-ph.IM↗

arXiv2022

On the LISA science performance in observations of short-lived signals from massive black hole binary coalescences

The observation of massive black hole binary systems is one of the main science objectives of the Laser Interferometer Space Antenna (LISA). The instrument's design requirements have recently been revised: they set a requirement at $0.1\,\mathrm{mHz}$, with no additional explicit requirements at lower frequencies. This has implications for observations of the short-lived signals produced by the coalescence of massive and high-redshift binaries. Here we consider the most pessimistic scenario: the (unlikely) case in which LISA has no sensitivity below $0.1\,\mathrm{mHz}$. We show that the presence of higher multipoles (beyond the dominant $\ell = |m| = 2$ mode) in the gravitational radiation from these systems, which will be detectable with a total signal-to-noise ratio $\sim 10^3$, allows LISA to retain the capability to accurately measure the physical parameters, the redshift, and to constrain the sky location. To illustrate this point, we consider a few select binaries in a total (redshifted) mass range of $4 \times10^6 - 4 \times 10^7\,M_\odot$ whose ($\ell = |m| = 2$) gravitational-wave signals last between $\approx 12$ hours and $\approx 20$ days in band. We model the emitted gravitational radiation using the highly accurate (spin-aligned) waveform approximant IMRPhenomXHM and carry out a fully coherent Bayesian analysis on the LISA noise-orthogonal time-delay-interferometry channels.

gr-qc↗

arXiv2022

Identifying LISA verification binaries among the Galactic population of double white dwarfs

Double white dwarfs (DWDs) will be the most numerous gravitational-wave (GW) sources for the Laser Interferometer Space Antenna (LISA). Most of the Galactic DWDs will be unresolved and will superpose to form a confusion noise foreground, the dominant LISA noise source around $\sim 0.5\mathrm{-}3\,\mathrm{mHz}$. A small fraction of these sources will stand out from the background and be individually detectable. Uniquely among GW sources, a handful of these binaries will be known in advance from electromagnetic (EM) observations and will be guaranteed sources of detectable GWs in the LISA band; these are known as verification binaries (VBs). High-cadence photometric surveys are continuously discovering new VB systems, and their number will continue to grow ahead of the launch of LISA. We analyse, in a fully Bayesian framework, all the currently known VB candidates with the latest design requirements for the LISA mission and find that 25 of the considered sources can be detected within a $4\,\mathrm{yr}$ observation time. We explore what can be expected from GW observations, both alone and in combination with EM observations, and estimate the VB's time to detection in the early months of LISA operations. We also show how VBs can be analysed in the case where their GW signals compete with many other unknown binary signals (both resolved and unresolved) from a realistic Galactic population of DWDs.

astro-ph.SR↗

arXiv2022

The last three years: multiband gravitational-wave observations of stellar-mass binary black holes

Understanding the formation and evolution of the stellar-mass binary black holes discovered by LIGO and Virgo is a challenge that spans many areas of astrophysics, from stellar evolution, dynamics and accretion disks, to possible exotic early universe processes. Over the final years of their lives, stellar-mass binaries radiate gravitational waves that are first observable by space-based detectors (such as LISA) and then ground-based instruments (such as LIGO, Virgo and the next generation observatories Cosmic Explorer and the Einstein Telescope). Using state-of-the-art waveform models and parameter-estimation pipelines for both ground- and space-based observations, we show that (the expected handful of) these multiband observations will allow at least percent-level measurements of all 17 parameters that describe the binary, the possible identification of a likely host galaxy, and the forewarning of the merger days in advance allowing telescopes at multiple wavelengths to search for any electromagnetic signature associated to it. Multiband sources will therefore be a gold mine for astrophysics, but we also show that they could be less useful as laboratories for fundamental tests of general relativity than has been previously suggested.

astro-ph.HE↗

arXiv2021

Bayesian parameter estimation of stellar-mass black-hole binaries with LISA

We present a Bayesian parameter-estimation pipeline to measure the properties of inspiralling stellar-mass black hole binaries with LISA. Our strategy (i) is based on the coherent analysis of the three noise-orthogonal LISA data streams, (ii) employs accurate and computationally efficient post-Newtonian waveforms accounting for both spin-precession and orbital eccentricity, and (iii) relies on a nested sampling algorithm for the computation of model evidences and posterior probability density functions of the full 17 parameters describing a binary. We demonstrate the performance of this approach by analyzing the LISA Data Challenge (LDC-1) dataset, consisting of 66 quasi-circular, spin-aligned binaries with signal-to-noise ratios ranging from 3 to 14 and times to merger ranging from 3000 to 2 years. We recover 22 binaries with signal-to-noise ratio higher than 8. Their chirp masses are typically measured to better than $0.02 M_\odot$ at $90\%$ confidence, while the sky-location accuracy ranges from 1 to 100 square degrees. The mass ratio and the spin parameters can only be constrained for sources that merge during the mission lifetime. In addition, we report on the successful recovery of an eccentric, spin-precessing source at signal-to-noise ratio 15 for which we can measure an eccentricity of $3\times 10^{-3}$.

astro-ph.HE↗

arXiv2021

Ultra-low frequency gravitational waves from cosmological and astrophysical processes

Gravitational waves (GWs) at ultra-low frequencies (${\lesssim 100\,\mathrm{nHz}}$) are key to understanding the assembly and evolution of astrophysical black hole (BH) binaries with masses $\sim 10^{6}-10^{9}\,M_\odot$ at low redshifts. These GWs also offer a unique window into a wide variety of cosmological processes. Pulsar timing arrays (PTAs) are beginning to measure this stochastic signal at $\sim 1-100\,\mathrm{nHz}$ and the combination of data from several arrays is expected to confirm a detection in the next few years. The dominant physical processes generating gravitational radiation at $\mathrm{nHz}$ frequencies are still uncertain. PTA observations alone are currently unable to distinguish a binary BH astrophysical foreground from a cosmological background due to, say, a first order phase transition at a temperature $\sim 1-100\,\mathrm{MeV}$ in a weakly-interacting dark sector. This letter explores the extent to which incorporating integrated bounds on the ultra-low frequency GW spectrum from any combination of cosmic microwave background, big bang nucleosynethesis or astrometric observations can help to break this degeneracy.

astro-ph.CO↗

arXiv2021

High mass but low spin: an exclusion region to rule out hierarchical black-hole mergers as a mechanism to populate the pair-instability mass gap

The occurrence of pair-instability supernovae is predicted to prevent the formation of black holes with masses $\gtrsim 50 M_\odot$. Recent gravitational-wave detections in this mass range require an explanation beyond that of standard stellar collapse. Current modeling strategies include the hierarchical assembly of previous generations of black-hole mergers as well as other mechanisms of astrophysical nature (lowered nuclear-reaction rates, envelope retention, stellar mergers, accretion, dredge-up episodes). In this paper, we point out the occurrence of an exclusion region that cannot be easily populated by hierarchical black-hole mergers. A future gravitational-wave detection of a black hole with mass $\gtrsim 50M_\odot$ and spin $\lesssim 0.2$ will indicate that the pair-instability mass gap is polluted in some other way. Such a putative outlier can be explained using hierarchical mergers only with considerable fine-tuning of both mass ratio and spins of the preceding black-hole merger -- an assumption that can then be cross-checked against the bulk of the gravitational-wave catalog.

astro-ph.HE↗

arXiv2020

Massive black hole binary systems and the NANOGrav 12.5 year results

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has recently reported evidence for the presence of a common stochastic signal across their array of pulsars. The origin of this signal is still unclear. One of the possibilities is that it is due to a stochastic gravitational wave background (SGWB) in the $\sim 1-10\,{\rm nHz}$ frequency region. Taking the NANOGrav observational result at face value, we show that this signal would be fully consistent with a SGWB produced by an unresolved population of in-spiralling massive black hole binaries (MBHBs) predicted by current theoretical models. Considering an astrophysically agnostic model we find that the MBHB merger rate is loosely constrained to the range $10^{-11} - 2$ $\mathrm{Mpc}^{-3}\,\mathrm{Gyr}^{-1}$. Including additional constraints from galaxy pairing fractions and MBH-bulge scaling relations, we find that the MBHB merger rate is $10^{-5} - 5\times10^{-4}$ $\mathrm{Mpc}^{-3}\,\mathrm{Gyr}^{-1}$, the MBHB merger time-scale is $\le 3\,\mathrm{Gyr}$ and the norm of the $M_\mathrm{BH}-M_\mathrm{bulge}$ relation $\ge 1.2\times 10^{8}\,M_\odot$ (all intervals quoted at 90\% confidence). Regardless of the astrophysical details of MBHB assembly, this result would imply that a sufficiently large population of massive black holes pair up, form binaries and merge within a Hubble time.

astro-ph.HE↗

arXiv2020

Constraining the lensing of binary neutron stars from their stochastic background

Gravitational wave (GW) transients from binary neutron star (BNS) coalescences can, in principle, be subject to gravitational lensing thereby increasing the amplitude and signal-to-noise ratio. We estimate the rate of lensed BNS events resolvable by LIGO and Virgo and find that it is constrained by the current non-detection of a stochastic GW background. Following closely the formalism we developed (10.1103/PhysRevLett.125.141102) in the context of binary black hole lensing, we show that at current sensitivities the fraction of BNS coalescences with lensing magnifications $\mu> 1.02$ is less than $\sim 7\times 10^{-8}$ and therefore such events should not be expected in the near future. We also make predictions for projected future sensitivities.

astro-ph.HE↗