arXiv subjects

Federico De Lillo

Publications and source records attributed to Federico De Lillo.

13 recordsLinked to original sources

arXiv2026

Popcorn in the sky: Identifying primordial black holes in the gravitational-wave background

Primordial black holes (PBHs) are possible sources of a gravitational-wave background (GWB), detectable with the next observing runs of LIGO--Virgo--KAGRA. In case of a detection, it will be crucial to distinguish the possible sources of this GWB. One under-explored possibility is to exploit the duty cycle that quantifies the number of sources present in the time domain signal, which can be very different depending on the nature and population of the sources. We compute the duty cycle for a realistic population of PBH binaries, isolating the shot-noise, popcorn and continuous contributions to the GWB. We identify the dependence of the duty cycle on the signal frequency, duration and amplitude as a crucial metric for distinguishing PBHs from other sources in the GWB and constraining PBH models. Our work motivates the development of specific analysis tools to extract these observables, in order to unlock new cosmological insights with upcoming GW data.

astro-ph.CO↗

arXiv2025

Impact of correlated magnetic noise on directional stochastic gravitational-wave background searches

One potential factor that could impede searches for the stochastic gravitational-wave background (SGWB), arising from the incoherent superposition of a multitude of weak and unresolvable gravitational-wave signals in the Universe, is correlated magnetic noise at Earth-scale distances, such as the Schumann resonances. As the sensitivity of terrestrial detectors to SGWBs increases, these effects are expected to become even more pronounced, emphasizing the importance of considering correlated noise sources in SGWB searches. In this study, we explore for the first time the impact of this class of noise on anisotropic SGWB searches. We focus on the low-frequency range of 20-200 Hz with a resolution of 1/32 Hz, using data from the LEMI-120 and Metronix MFS-06e magnetometers, located at the sites of the Advanced LIGO and Advanced Virgo interferometers, respectively, during the third observing run. These measurements were then compared with the directional upper limit derived from gravitational-wave data collected during the third observing run of the LIGO-Virgo-KAGRA collaboration. The results indicate that the magnetic noise correlations are below the interferometers' sensitivity level during the O3 observing run. The potential impact of magnetic correlations on the Advanced LIGO detectors has also been investigated at the A+ design sensitivity level.

gr-qc↗

arXiv2025

Searching for continuous gravitational waves from highly deformed compact objects with DECIGO

Searches for continuous gravitational waves from isolated compact objects and those in binary systems aim to detect non-axisymmetric, deformed neutron stars at particular locations in the Galaxy or all-sky. However, a large fraction of known pulsars have rotational frequencies that lie outside the audio frequency band, rendering current detectors insensitive to these pulsars. In this work, we show that DECIGO, a future space-based deci-hertz gravitational-wave interferometer, will be sensitive to severely deformed compact objects, e.g. hybrid stars, neutron stars, or magnetars. We estimate the number of possible compact objects that could be detected with such high deformations, both via their individual continuous gravitational-wave emission and the stochastic gravitational-wave background created by a superposition of gravitational waves from the $\sim 10^8$ compact objects in the Galaxy. Furthermore, we show that the existence of such compact objects could be probed across a wide parameter space at a fraction of the computational cost of current searches for isolated compact objects and those in binary systems. For known pulsars, we will be able to both beat the spin-down limit and probe the Brans-Dicke modified theory of gravity parameter $ζ<1$ for approximately 85% of known pulsars with $f_{\rm gw}<10$ Hz, the latter of which is currently only possible for $O(10)$ pulsars. DECIGO will thus open a new window to probe highly deformed compact objects and over half of the known pulsars, both of which are currently inaccessible to ground-based detectors.

gr-qc↗

arXiv2024

Gravitational wave constraints on planetary-mass primordial black holes using LIGO O3a data

Gravitational waves from sub-solar mass inspiraling compact objects would provide almost smoking-gun evidence for primordial black holes (PBHs). We perform the first search for inspiraling planetary-mass compact objects in equal-mass and highly asymmetric mass-ratio binaries using data from the first half of the LIGO-Virgo-KAGRA third observing run. Though we do not find any significant candidates, we determine the maximum luminosity distance reachable with our search to be of $O(0.1-100)$ kpc, and corresponding model-independent upper limits on the merger rate densities to be $O(10^{3}-10^{-7})$ kpc$^{-3}$yr$^{-1}$ for systems with chirp masses of $O(10^{-4}-10^{-2})M_\odot$, respectively. Furthermore, we interpret these rate densities as arising from PBH binaries and constrain the fraction of dark matter that such objects could comprise. For equal-mass PBH binaries, we find that these objects would compose less than 4-100% of DM for PBH masses of $10^{-2}M_\odot$ to $2\times 10^{-3}M_\odot$, respectively. For asymmetric binaries, assuming one black hole mass corresponds to a peak in the mass function at 2.5$M_\odot$, a PBH dark-matter fraction of 10% and a second, much lighter PBH, we constrain the mass function of the second PBH to be less than 1 for masses between $1.5\times 10^{-5}M_\odot$ and $2\times 10^{-4}M_\odot$. Our constraints, released on Zenodo, are robust enough to be applied to any PBH or exotic compact object binary formation models, and complement existence microlensing results. More details about our search can be found in our companion paper.

gr-qc↗

arXiv2024

Method to search for inspiraling planetary-mass ultra-compact binaries using the generalized frequency-Hough transform in LIGO O3a data

Gravitational waves from sub-solar mass primordial black holes could be detected in LIGO, Virgo and KAGRA data. Here, we apply a method originally designed to look for rapidly spinning-down neutron stars, the generalized frequency-Hough transform, to search for planetary-mass primordial black holes using data from the first half of the third observing run of advanced LIGO. In this companion paper to arXiv:2402.19468, in which the main results of our search are presented, we delve into the details of the search methodology, the choices we have made regarding the parameter space to explore, the follow-up procedure we use to confirm or reject possible candidates returned in our search, and a comparison of our analytic procedure of generating upper limits to those obtained through injections.

astro-ph.IM↗

arXiv2024

Estimating Astrophysical Population Properties using a multi-component Stochastic Gravitational-Wave Background Search

The recent start of the fourth observing run of the LIGO-Virgo-KAGRA (LVK) collaboration has reopened the hunt for gravitational-wave (GW) signals, with one compact-binary-coalescence (CBC) signal expected to be observed every few days. Among the signals that could be detected for the first time there is the stochastic gravitational-wave background (SGWB) from the superposition of unresolvable GW signals that cannot be detected individually. In fact, multiple SGWBs are likely to arise given the variety of sources, making it crucial to identify the dominant components and assess their origin. However, most search methods with ground-based detectors assume the presence of one SGWB component at a time, which could lead to biased results in estimating its spectral shape if multiple SGWBs exist. Therefore, a joint estimate of the components is necessary. In this work, we adapt such an approach and analyse the data from the first three LVK observing runs, searching for a multi-component isotropic SGWB. We do not find evidence for any SGWB and establish upper limits on the dimensionless energy parameter $Ω_{\rm gw}(f)$ at 25 Hz for five different power-law spectral indices, $α= 0, \, 2/3,\, 2,\, 3,\, 4$, jointly. For the spectral indices $α= 2/3,\, 2, \, 4$, corresponding to astrophysical SGWBs from CBCs, r-mode instabilities in young rotating neutron stars, and magnetars, we draw further astrophysical implications by constraining the ensemble parameters $K_{\rm CBC}, \, K_{\rm r-modes}, \, K_{\rm magnetars}$, defined in the main text.

gr-qc↗

arXiv2023

Probing Ensemble Properties of Vortex-avalanche Pulsar Glitches with a Stochastic Gravitational-Wave Background Search

A stochastic gravitational-wave background (SGWB) is expected to be produced by the superposition of individually undetectable, unresolved gravitational-wave (GW) signals from cosmological and astrophysical sources. Such a signal can be searched with dedicated techniques using the data acquired by a network of ground-based GW detectors. In this work, we consider the astrophysical SGWB resulting from pulsar glitches, which are sudden increases in the rotational pulsar frequency, within our Galaxy. More specifically, we assume glitches to be associated with quantized, superfluid, vortex-avalanches in the pulsars, and we model the SGWB from the superposition of GW bursts emitted during the glitching phase. We perform a cross-correlation search for this SGWB-like signal employing the data from the first three observation runs of Advanced LIGO and Virgo. Not having found any evidence for a SGWB signal, we set upper limits on the dimensionless energy density parameter $Ω_{\mathrm{gw}}(f)$ for two different power-law SGWBs, corresponding to two different glitch regimes. We obtain $Ω_{\mathrm{gw}}(f)\leq 7.5 \times 10^{-10}$ at 25 Hz for a spectral index 5/2, and $Ω_{\mathrm{gw}}(f)\leq 5.7 \times 10^{-17}$ at 25 Hz for a spectral index 17/2. We then use these results to set constraints on the average glitch duration and the average radial motion of the vortices during the glitches for the population of the glitching Galactic pulsars, as a function of the Galactic glitch rate.

gr-qc↗

arXiv2023

pygwb: Python-based library for gravitational-wave background searches

The collection of gravitational waves (GWs) that are either too weak or too numerous to be individually resolved is commonly referred to as the gravitational-wave background (GWB). A confident detection and model-driven characterization of such a signal will provide invaluable information about the evolution of the Universe and the population of GW sources within it. We present a new, user-friendly Python--based package for gravitational-wave data analysis to search for an isotropic GWB in ground--based interferometer data. We employ cross-correlation spectra of GW detector pairs to construct an optimal estimator of the Gaussian and isotropic GWB, and Bayesian parameter estimation to constrain GWB models. The modularity and clarity of the code allow for both a shallow learning curve and flexibility in adjusting the analysis to one's own needs. We describe the individual modules which make up {\tt pygwb}, following the traditional steps of stochastic analyses carried out within the LIGO, Virgo, and KAGRA Collaboration. We then describe the built-in pipeline which combines the different modules and validate it with both mock data and real GW data from the O3 Advanced LIGO and Virgo observing run. We successfully recover all mock data injections and reproduce published results.

gr-qc↗

arXiv2022

Constraints on planetary and asteroid-mass primordial black holes from continuous gravitational-wave searches

We present new constraints on the merging rates of planetary-mass and asteroid-mass primordial black hole binaries using limits on continuous waves(quasi-monochromatic, quasi-infinite duration signals) derived from an all-sky search for isolated compact objects in the first six months of the third observing run (O3a) of LIGO/Virgo. We calculate the merging rates of these binaries in a model-independent way, and convert them to constraints on the primordial black hole abundance with minimal modelling assumptions. Our results show that we are sensitive to sources at most $\mathcal{O}(10$ pc) away for systems with chirp masses of $\mathcal{O}(10^{-5}M_\odot)$ at gravitational-wave frequencies around 30-40 Hz. These results also show that continuous-wave searches could in the future directly probe the existence of planetary-mass and asteroid-mass primordial black holes, especially those in binaries with asymmetric mass ratios. Furthermore, they demonstrate that new methods accounting for the full nonlinear gravitational-wave frequency evolution are needed to improve constraints on primordial black holes.

gr-qc↗

arXiv2022

Stochastic gravitational-wave background searches and constraints on neutron-star ellipticity

Rotating neutron stars (NSs) are promising sources of gravitational waves (GWs) in the frequency band of ground-based detectors. They are expected to emit quasi-monochromatic, long-duration GW signals, called continuous waves (CWs), due to their deviations from spherical symmetry. The degree of such deformations, and hence the information about the internal structure of a NS, is encoded in a dimensionless parameter $\varepsilon$ called ellipticity. Searches for CW signals from isolated Galactic NSs have shown to be sensitive to ellipticities as low as $\varepsilon \sim \mathcal{O}(10^{-9})$. These searches are optimal for detecting and characterising GWs from individual NSs, but they are not designed to measure the properties of NSs as population, such as the average ellipticity $\varepsilon_{\mathrm{av}}$. These ensemble properties can be determined by the measurement of the stochastic gravitational-wave background (SGWB) arising from the superposition of GW signals from individually-undetectable NSs. In this work, we perform a cross-correlation search for such a SGWB using the data from the first three observation runs of Advanced LIGO and Virgo. Finding no evidence for a SGWB signal, we set upper limits on the dimensionless energy density parameter $Ω_{\mathrm{gw}}(f)$. Using these results, we also constrain the average ellipticity of Galactic NSs and five NS ``hotspots'', as a function of the number of NSs emitting GWs within the frequency band of the search $N_{\mathrm{band}}$. We find $\varepsilon_{\mathrm{av}} \lesssim 1.8 \times 10^{-8}$, with $N_{\mathrm{band}}=1.6 \times 10^7$, for Galactic NSs, and $\varepsilon_{\mathrm{av}} \lesssim [3.5-11.8]\times 10^{-7}$, with $N_{\mathrm{band}}=1.6 \times 10^{10}$, for NS hotspots.

gr-qc↗

arXiv2021

Probing planetary-mass primordial black holes with continuous gravitational waves

Gravitational waves can probe the existence of planetary-mass primordial black holes. Considering a mass range of $[10^{-7}-10^{-2}]M_\odot$, inspiraling primordial black holes could emit either continuous gravitational waves, quasi-monochromatic signals that last for many years, or transient continuous waves, signals whose frequency evolution follows a power law and last for $\mathcal{O}$(hours-months). We show that primordial black hole binaries in our galaxy may produce detectable gravitational waves for different mass functions and formation mechanisms. In order to detect these inspirals, we adapt methods originally designed to search for gravitational waves from asymmetrically rotating neutron stars. The first method, the Frequency-Hough, exploits the continuous, quasi-monochromatic nature of inspiraling black holes that are sufficiently light and far apart such that their orbital frequencies can be approximated as linear with a small spin-up. The second method, the Generalized Frequency-Hough, drops the assumption of linearity and allows the signal frequency to follow a power-law evolution. We explore the parameter space to which each method is sensitive, derive a theoretical sensitivity estimate, determine optimal search parameters and calculate the computational cost of all-sky and directed searches. We forecast limits on the abundance of primordial black holes within our galaxy, showing that we can constrain the fraction of dark matter that primordial black holes compose, $f_{\rm PBH}$, to be $f_{\rm PBH}\lesssim 1$ for chirp masses between $[4\times 10^{-5}-10^{-3}]M_\odot$ for current detectors. For the Einstein Telescope, we expect the constraints to improve to $f_{\rm PBH}\lesssim 10^{-2}$ for chirp masses between [$10^{-4}-10^{-3}]M_\odot$.

astro-ph.HE↗

arXiv2021

Probing new light gauge bosons with gravitational-wave interferometers using an adapted semi-coherent method

We adapt a method, originally developed for searches for quasi-monochromatic, quasi-infinite gravitational-wave signals, to directly detect new light gauge bosons with laser interferometers, which could be candidates for dark matter. To search for these particles, we optimally choose the analysis coherence time as a function of boson mass, such that all of the signal power will be confined to one frequency bin. We focus on the dark photon, a gauge boson that could couple to baryon or baryon-lepton number, and explain that its interactions with gravitational-wave interferometers result in a narrow-band, stochastic signal. We provide an end-to-end analysis scheme, estimate its computational cost, and investigate follow-up techniques to confirm or rule out dark matter candidates. Furthermore, we derive a theoretical estimate of the sensitivity, and show that it is consistent with both the empirical sensitivity determined through simulations, and results from a cross-correlation search. Finally, we place Feldman-Cousins upper limits using data from LIGO Livingston's second observing run, which give a new and strong constraint on the coupling of gauge bosons to the interferometer.

astro-ph.IM↗

arXiv2020

Vector boson fusion at multi-TeV muon colliders

High-energy lepton colliders with a centre-of-mass energy in the multi-TeV range are currently considered among the most challenging and far-reaching future accelerator projects. Studies performed so far have mostly focused on the reach for new phenomena in lepton-antilepton annihilation channels. In this work we observe that starting from collider energies of a few TeV, electroweak (EW) vector boson fusion/scattering (VBF) at lepton colliders becomes the dominant production mode for all Standard Model processes relevant to studying the EW sector. In many cases we find that this also holds for new physics. We quantify the size and the growth of VBF cross sections with collider energy for a number of SM and new physics processes. By considering luminosity scenarios achievable at a muon collider, we conclude that such a machine would effectively be a "high-luminosity weak boson collider," and subsequently offer a wide range of opportunities to precisely measure EW and Higgs coupling as well as to discover new particles.

hep-ph↗