arXiv subjects

Alvise Raccanelli

Publications and source records attributed to Alvise Raccanelli.

At least 37 records · Page 2Linked to original sources

arXiv2023

Signatures of primordial black holes in gravitational wave clustering

The possible existence of primordial black holes (PBHs) is an open question in modern cosmology. Among the probes to test it, gravitational waves (GW) coming from their mergers constitute a powerful tool. In this work, we study how stellar mass PBH binaries could affect measurements of the clustering of merger events in future GW surveys. We account for PBH binaries formed both in the early and late Universe and show that the power spectrum modification they introduce can be detected at $\sim 2σ-3σ$ (depending on some assumptions) whenever PBH mergers make up at least $\sim 60\%$ of the overall number of detected events. By adding cross-correlations with galaxy surveys, this threshold is lowered to $\sim 40\%$. In the case of a poor redshift determination of GW sources, constraints are degraded by about a factor of 2. Assuming a theoretical model for the PBH merger rate, we can convert our results to constraints on the fraction of dark matter in PBHs, $f_{\rm PBH}$. Finally, we perform a Bayesian model selection forecast and confirm that the analysis we develop could be able to detect $\sim30M_\odot$ PBHs if they account for $f_{\rm PBH}\sim 10^{-4}-10^{-3}$, depending on the model uncertainty considered, being thus competitive with other probes.

astro-ph.CO↗

arXiv2023

On the asymptotic connection between full- and flat-sky angular correlators

We investigate the connection between the full- and flat-sky angular power spectra. First, we revisit this connection established on the geometric and physical grounds, namely that the angular correlations on the sphere and in the plane (flat-sky approximation) correspond to each other in the limiting case of small angles and a distant observer. To establish the formal conditions for this limit, we first resort to a simplified shape of the 3D power spectrum, which allows us to obtain analytic results for both the full- and flat-sky angular power spectra. Using a saddle-point approximation, we find that the flat-sky results are obtained in the limit when the comoving distance and wave modes $\ell$ approach infinity at the same rate. This allows us to obtain an analogous asymptotic expansion of the full-sky angular power spectrum for general 3D power spectrum shapes, including the LCDM Universe. In this way, we find a robust limit of correspondence between the full- and flat-sky results. These results also establish a mathematical relation, i.e., an asymptotic expansion of the ordinary hypergeometric function of a particular choice of arguments that physically corresponds to the flat-sky approximation of a distant observer. This asymptotic form of the ordinary hypergeometric function is obtained in two ways: relying on our saddle-point approximation and using some of the known properties of the hypergeometric function.

astro-ph.CO↗

arXiv2023

The observed power spectrum & frequency-angular power spectrum

The two-point summary statistics is one of the most commonly used tools in the study of cosmological structure. Starting from the theoretical power spectrum defined in the 3D volume and obtained via the process of ensemble averaging, we establish the construction of the observed 3D power spectrum, folding the unequal-time information around the average position into the wave modes along the line of sight. We show how these unequal-time cross-correlation effects give rise to scale-dependent corrections in the observable 3D power spectrum. We also introduce a new dimensionless observable, the frequency-angular power spectrum, which is a function of dimensionless and directly observable quantities corresponding to Fourier counterparts of angles and redshifts. While inheriting many useful characteristics of the canonical observed power spectrum, this newly introduced statistic does not depend on physical distances and is hence free of so-called Alcock-Paczynski effects. Such observable thus presents a clear advantage and simplification over the traditional power spectrum. Moreover, relying on linear theory calculations, we estimate that unequal-time corrections, while generally small, can amount to a few percent on large scales and high redshifts. Interestingly, such corrections depend on the bias of the tracers, the growth rate, but also their time derivatives, opening up the possibility of new tests of cosmological models. These radial mode effects also introduce anisotropies in the observed power spectrum, in addition to the ones arising from redshift-space distortions, generating non-vanishing odd multiples and imaginary contributions. Lastly, we investigate the effects of unequal-time corrections in resumming long displacements (IR-resummation) of the observed power spectrum.

astro-ph.CO↗

arXiv2023

Power spectrum in the cave

Forthcoming galaxy surveys will provide measurements of galaxy clustering with an unprecedented level of precision, that will require comparably good accuracy. Current models for galaxy correlations rely on approximations and idealizations that might be inadequate for ultra precise measurements. On the other hand, exact calculations have proven to be computationally too expensive to be efficiently implemented in real data analyses. We start a project to provide precise and accurate formalisms for galaxy correlations, and in this paper we investigate the 3D angular power spectrum including effects of unequal time correlations. We establish an explicit link between the full- and flat-sky spectra by performing an asymptotic expansion of the full-sky result around the equal time case. The limiting case coincides with the idealized spectrum that a meta-observer would measure if it had access to the entire 4D Universe. The leading term in the obtained flat-sky expansion is the only translationally invariant term in the plane perpendicular to the line of sight, while the higher-order terms account for the deviation from this invariance. We study the behavior of such corrections for a simplified universe where we can analytically solve the power spectrum and have full control of the equations, therefore being able to understand the exact nature of all the terms and the origin of the corrections. We highlight that the conclusions and the structure of the unequal time spectra are fully general and serve as lessons and guidance in understanding galaxy clustering in any cosmology. Finally, we show that our flat-sky unequal time expression matches the exact full-sky calculation remarkably better than commonly adopted approximations, even at the largest scales and for both shallow and deep redshift bins.

astro-ph.CO↗

arXiv2022

The effect of outflows on CMB bounds from Primordial Black Hole accretion

Should Primordial Black Holes (PBHs) exist in nature, they would inevitably accrete baryonic matter in their vicinity. In turn, the consequent emission of high-energy radiation could affect the thermal history of the universe to an extent that can be probed with a number of cosmological observables such as the Cosmic Microwave Background (CMB) anisotropies. However, our understanding of the accretion and radiation emission processes in the context of PBHs is still in its infancy, and very large theoretical uncertainties affect the resulting constraints on the PBH abundance. Building on state-of-the-art literature, in this work we take a step towards the development of a more realistic picture of PBH accretion by accounting for the contribution of outflows. Specifically, we derive CMB-driven constraints on the PBH abundance for various accretion geometries, ionization models and mass distributions in absence and in presence of mechanical feedback and non-thermal emissions due to the outflows. As a result, we show that the presence of such outflows introduces an additional layer of uncertainty that needs to be taken into account when quoting cosmological constraints on the PBH abundance, with important consequences in particular in the LIGO-Virgo-KAGRA observational window.

astro-ph.CO↗

arXiv2022

Projection effects on the observed angular spectrum of the astrophysical stochastic gravitational wave background

The detection and characterization of the Stochastic Gravitational Wave Background (SGWB) is one of the main goals of Gravitational Wave (GW) experiments. The observed SGWB will be the combination of GWs from cosmological (as predicted by many models describing the physics of the early Universe) and astrophysical origins, which will arise from the superposition of GWs from unresolved sources whose signal is too faint to be detected. Therefore, it is important to have a proper modeling of the astrophysical SGWB (ASGWB) in order to disentangle the two signals; moreover, this will provide additional information on astrophysical properties of compact objects. Applying the Cosmic Rulers formalism, we compute the observed ASGWB angular power spectrum, hence using gauge invariant quantities, accounting for all effects intervening between the source and the observer. These are the so-called projection effects, which include Kaiser, Doppler and gravitational potentials effect. Our results show that these projection effects are the most important at the largest scales, and they contribute to up to tens of percent of the angular power spectrum amplitude, with the Kaiser term being the largest at all scales. While the exact impact of these results will depend on instrumental and astrophysical details, a precise theoretical modeling of the ASGWB will necessarily need to include all these projection effects.

astro-ph.CO↗

arXiv2022

New Horizons for Fundamental Physics with LISA

The Laser Interferometer Space Antenna (LISA) has the potential to reveal wonders about the fundamental theory of nature at play in the extreme gravity regime, where the gravitational interaction is both strong and dynamical. In this white paper, the Fundamental Physics Working Group of the LISA Consortium summarizes the current topics in fundamental physics where LISA observations of GWs can be expected to provide key input. We provide the briefest of reviews to then delineate avenues for future research directions and to discuss connections between this working group, other working groups and the consortium work package teams. These connections must be developed for LISA to live up to its science potential in these areas.

gr-qc↗

arXiv2022

Cosmology with the Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational wave observations by LISA to probe the universe.

astro-ph.CO↗

arXiv2022

Gravitational waves $\times$ HI intensity mapping: cosmological and astrophysical applications

Two of the most rapidly growing observables in cosmology and astrophysics are gravitational waves (GW) and the neutral hydrogen (HI) distribution. In this work, we investigate the cross-correlation between resolved gravitational wave detections and HI signal from intensity mapping (IM) experiments. By using a tomographic approach with angular power spectra, including all projection effects, we explore possible applications of the combination of the Einstein Telescope and the SKAO intensity mapping surveys. We focus on three main topics: \textit{(i)} statistical inference of the observed redshift distribution of GWs; \textit{(ii)} constraints on dynamical dark energy models as an example of cosmological studies; \textit{(iii)} determination of the nature of the progenitors of merging binary black holes, distinguishing between primordial and astrophysical origin. Our results show that: \textit{(i)} the GW redshift distribution can be calibrated with good accuracy at low redshifts, without any assumptions on cosmology or astrophysics, potentially providing a way to probe astrophysical and cosmological models; \textit{(ii)} the constrains on the dynamical dark energy parameters are competitive with IM-only experiments, in a complementary way and potentially with less systematics; \textit{(iii)} it will be possible to detect a relatively small abundance of primordial black holes within the gravitational waves from resolved mergers. Our results extend towards $\mathrm{GW \times IM}$ the promising field of multi-tracing cosmology and astrophysics, which has the major advantage of allowing scientific investigations in ways that would not be possible by looking at single observables separately.

astro-ph.CO↗

arXiv2021

CLASS_GWB: robust modeling of the astrophysical gravitational wave background anisotropies

Gravitational radiation offers a unique possibility to study the large-scale structure of the Universe, gravitational wave sources and propagation in a completely novel way. Given that gravitational wave maps contain a wealth of astrophysical and cosmological information, interpreting this signal requires a non-trivial multidisciplinary approach. In this work we present the complete computation of the signal produced by compact object mergers accounting for a detailed modelling of the astrophysical sources and for cosmological perturbations. We develop the CLASS_GWB code, which allows for the computation of the anisotropies of the astrophysical gravitational wave background, accounting for source and detector properties, as well as effects of gravitational wave propagation. We apply our numerical tools to robustly compute the angular power spectrum of the anisotropies of the gravitational wave background generated by astrophysical sources in the LIGO-Virgo frequency band. The end-to-end theoretical framework we present can be easily applied to different sources and detectors in other frequency bands. Moreover, the same numerical tools can be used to compute the anisotropies of gravitational wave maps of the sky made using resolved events.

gr-qc↗

arXiv2020

Beware of commonly used approximations I: errors in forecasts

In the era of precision cosmology, establishing the correct magnitude of statistical errors in cosmological parameters is of crucial importance. However, widely used approximations in galaxy surveys analyses can lead to parameter uncertainties that are grossly mis-estimated, even in a regime where the theory is well understood (e.g., linear scales). These approximations can be introduced at three different levels: in the form of the likelihood, in the theoretical modelling of the observable and in the numerical computation of the observable. Their consequences are important both in data analysis through e.g., Markov Chain Monte Carlo parameter inference, and when survey instrument and strategy are designed and their constraining power on cosmological parameters is forecasted, for instance using Fisher matrix analyses. In this work, considering the galaxy angular power spectrum as the target observable, we report one example of approximation for each of such three categories: neglecting off-diagonal terms in the covariance matrix, neglecting cosmic magnification and using the Limber approximation on large scales. We show that these commonly used approximations affect the robustness of the analysis and lead, perhaps counter-intuitively, to unacceptably large mis-estimates of parameters errors (from few~$10\%$ up to few~$100\%$) and correlations. Furthermore, these approximations might even spoil the benefits of the nascent multi-tracer and multi-messenger cosmology. Hence we recommend that the type of analysis presented here should be repeated for every approximation adopted in survey design or data analysis, to quantify how it may affect the results. To this aim, we have developed \texttt{Multi\_CLASS}, a new extension of \texttt{CLASS} that includes the angular power spectrum for multiple (galaxy and other tracers such as gravitational waves) populations.

astro-ph.CO↗

arXiv2020

Beware of commonly used approximations II: estimating systematic biases in the best-fit parameters

Cosmological parameter estimation from forthcoming experiments promise to reach much greater precision than current constraints. As statistical errors shrink, the required control over systematic errors increases. Therefore, models or approximations that were sufficiently accurate so far, may introduce significant systematic biases in the parameter best-fit values and jeopardize the robustness of cosmological analyses. We present a general expression to estimate a priori the systematic error introduced in parameter inference due to the use of insufficiently good approximations in the computation of the observable of interest or the assumption of an incorrect underlying model. Although this methodology can be applied to measurements of any scientific field, we illustrate its power by studying the effect of modeling the angular galaxy power spectrum incorrectly. We also introduce Multi_CLASS, a new, public modification of the Boltzmann code CLASS, which includes the possibility to compute angular cross-power spectra for two different tracers. We find that significant biases in most of the cosmological parameters are introduced if one assumes the Limber approximation or neglects lensing magnification in modern galaxy survey analyses, and the effect is in general larger for the multi-tracer case, especially for the parameter controlling primordial non-Gaussianity of the local type, $f_{\rm NL}$.

astro-ph.CO↗

arXiv2020

GW$\times$LSS: Chasing the Progenitors of Merging Binary Black Holes

Are the stellar-mass merging binary black holes, recently detected by their gravitational wave signal, of stellar or primordial origin? Answering this question will have profound implications for our understanding of the Universe, including the nature of dark matter, the early Universe and stellar evolution. We build on the idea that the clustering properties of merging binary black holes can provide information about binary formation mechanisms and origin. The cross-correlation of galaxy with gravitational wave catalogues carries information about whether black hole mergers trace more closely the distribution of dark matter -- indicative of primordial origin -- or that of stars harboured in luminous and massive galaxies -- indicative of a stellar origin. We forecast the detectability of such signal for several forthcoming and future gravitational wave interferometers and galaxy surveys, including, for the first time in such analyses, an accurate modelling for the different merger rates, lensing magnification and other general relativistic effects. Our results show that forthcoming experiments could allow us to test most of the parameter space of the still viable models investigated, and shed more light on the issue of binary black hole origin and evolution.

astro-ph.CO↗

arXiv2019

Enlightening the dark ages with dark matter

Constraints on dark matter annihilation or decay offer unique insights into the nature of dark matter. We illustrate how surveys dedicated to detect the highly redshifted 21 cm signal from the dark ages will offer a new window into properties of particle dark matter. The 21 cm intensity mapping signal and its fluctuations are sensitive to energy injection from annihilation or decay of long-lived particles in a way that is complementary to other probes. We present forecasted constraints from forthcoming and next-generation radio surveys. We show that, while SKA might be capable of a detection for some cases, the most promising opportunity to detect dark matter in the 21 cm intensity mapping signal is with a futuristic radio array on the lunar far-side, with the potential to detect a signal many orders of magnitude weaker than current or maximal constraints from other probes.

astro-ph.CO↗

arXiv2019

BE-HaPPY: Bias Emulator for Halo Power Spectrum including massive neutrinos

We study the clustering properties of dark matter halos in real- and redshift-space in cosmologies with massless and massive neutrinos through a large set of state-of-the-art N-body simulations. We provide quick and easy-to-use prescriptions for the halo bias on linear and mildly non-linear scales, both in real and redshift space, which are valid also for massive neutrinos cosmologies. Finally we present a halo bias emulator,$\textbf{BE-HaPPY}$, calibrated on the N-body simulations, which is fast enough to be used in the standard Markov Chain Monte Carlo approach to cosmological inference. For a fiducial standard $Λ$CDM cosmology $\textbf{BE-HaPPY}$ provides percent or sub-percent accuracy on the scales of interest (linear and well into the mildly non-linear regime), meeting therefore for the halo-bias the accuracy requirements for the analysis of next-generation large--scale structure surveys.

astro-ph.CO↗

arXiv2019

From Primordial Black Holes Abundance to Primordial Curvature Power Spectrum (and back)

In the model where Primordial Black Holes (PBHs) form from large primordial curvature (C) perturbations, i.e., CPBHs, constraints on PBH abundance provide in principle constraints on the primordial curvature power spectrum. This connection however depends necessarily on the details of PBH formation mechanism. In this paper we provide, for the first time, constraints on the primordial curvature power spectrum from the latest limits on PBH abundance, taking into account all the steps from gravitational collapse in real space to PBH formation. In particular, we use results from numerical relativity simulations and peak theory to study the conditions for PBH formation for a range of perturbation shapes, including non-linearities, perturbation profile and a careful treatment of smoothing and filtering scales. We then obtain updated PBH formation conditions and translate that into primordial spectrum constraints for a wide range of shapes and abundances. These updated constraints cover a range of scales not probed by other cosmological observables. Our results show that the correct and accurate modelling of non-linearities, filtering and typical perturbation profile, is crucial for deriving meaningful cosmological implications.

astro-ph.CO↗

arXiv2019

Cosmological perturbation effects on gravitational-wave luminosity distance estimates

Waveforms of gravitational waves provide information about a variety of parameters for the binary system merging. However, standard calculations have been performed assuming a FLRW universe with no perturbations. In reality this assumption should be dropped: we show that the inclusion of cosmological perturbations translates into corrections to the estimate of astrophysical parameters derived for the merging binary systems. We compute corrections to the estimate of the luminosity distance due to velocity, volume, lensing and gravitational potential effects. Our results show that the amplitude of the corrections will be negligible for current instruments, mildly important for experiments like the planned DECIGO, and very important for future ones such as the Big Bang Observer.

gr-qc↗

arXiv2019

Unveiling the Gravitational Universe at μ-Hz Frequencies

We propose a space-based interferometer surveying the gravitational wave (GW) sky in the milli-Hz to $μ$-Hz frequency range. By the 2040s', the $μ$-Hz frequency band, bracketed in between the Laser Interferometer Space Antenna (LISA) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant GW spectrum. Yet many outstanding questions related to astrophysics and cosmology are best answered by GW observations in this band. We show that a $μ$-Hz GW detector will be a truly overarching observatory for the scientific community at large, greatly extending the potential of LISA. Conceived to detect massive black hole binaries from their early inspiral with high signal-to-noise ratio, and low-frequency stellar binaries in the Galaxy, this instrument will be a cornerstone for multimessenger astronomy from the solar neighbourhood to the high-redshift Universe.

astro-ph.IM↗