# Davide Gerosa - Dipartimento di Fisica, Universita' Degli Studi di Milano, Milano, Italy

## Contact Details

NameDavide Gerosa |
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AffiliationDipartimento di Fisica, Universita' Degli Studi di Milano, Milano, Italy |
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CityMilano |
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CountryItaly |
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## Pubs By Year |
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## Pub CategoriesGeneral Relativity and Quantum Cosmology (18) High Energy Astrophysical Phenomena (17) Astrophysics of Galaxies (7) Cosmology and Nongalactic Astrophysics (5) High Energy Physics - Theory (2) High Energy Physics - Phenomenology (2) Solar and Stellar Astrophysics (1) |

## Publications Authored By Davide Gerosa

In the post-Newtonian (PN) regime, the timescale on which the spins of binary black holes precess is much shorter than the radiation-reaction timescale on which the black holes inspiral to smaller separations. On the precession timescale, the angle between the total and orbital angular momenta oscillates with nutation period $\tau$, during which the orbital angular momentum precesses about the total angular momentum by an angle $\alpha$. This defines two distinct frequencies that vary on the radiation-reaction timescale: the nutation frequency $\omega \equiv 2\pi/\tau$ and the precession frequency $\Omega \equiv \alpha/\tau$. Read More

The inferred parameters of the binary black hole GW151226 are consistent with nonzero spin for the most massive black hole, misaligned from the binary's orbital angular momentum. If the black holes formed through isolated binary evolution from an initially aligned binary star, this misalignment would then arise from a kick imparted to the first-born black hole at its birth during stellar collapse. We use simple kinematic arguments to constrain the characteristic magnitude of this kick, and find that a natal kick $v_k \gtrsim 50$ km/s must be imparted to the black hole at birth to produce misalignments consistent with GW151226. Read More

Advanced LIGO detectors at Hanford and Livingston made two confirmed and one marginal detection of binary black holes during their first observing run. The first event, GW150914, was from the merger of two black holes much heavier that those whose masses have been estimated so far, indicating a formation scenario that might differ from "ordinary" stellar evolution. One possibility is that these heavy black holes resulted from a previous merger. Read More

We analyze the inspiral dynamics of equal-mass precessing black-hole binaries using multi-timescale techniques. The orbit-averaged post-Newtonian evolutionary equations admit two constants of motion in the equal-mass limit, namely the magnitude of the total spin $S$ and the effective spin $\xi$. This feature makes the entire dynamics qualitatively different compared to the generic unequal-mass case, where only $\xi$ is constant while the variable $S$ parametrizes the precession dynamics. Read More

Generic black hole binaries radiate gravitational waves anisotropically, imparting a recoil, or kick, velocity to the merger remnant. If a component of the kick along the line of sight is present, gravitational waves emitted during the final orbits and merger will be gradually Doppler shifted as the kick builds up. We develop a simple prescription to capture this effect in existing waveform models, showing that future gravitational wave experiments will be able to perform direct measurements, not only of the black hole kick velocity, but also of its accumulation profile. Read More

We present the numerical code PRECESSION: a new open-source python module to study the dynamics of precessing black-hole binaries in the post-Newtonian regime. The code provides a comprehensive toolbox to (i) study the evolution of the black-hole spins along their precession cycles, (ii) perform gravitational-wave driven binary inspirals using both orbit-averaged and precession-averaged integrations, and (iii) predict the properties of the merger remnant through fitting formulae obtained from numerical-relativity simulations. PRECESSION is a ready-to-use tool to add the black-hole spin dynamics to larger-scale numerical studies such as gravitational-wave parameter estimation codes, population synthesis models to predict gravitational-wave event rates, galaxy merger trees and cosmological simulations of structure formation. Read More

We present numerical-relativity simulations of spherically symmetric core collapse and compact-object formation in scalar-tensor theories of gravity. The additional scalar degree of freedom introduces a propagating monopole gravitational-wave mode. Detection of monopole scalar waves with current and future gravitational-wave experiments may constitute smoking gun evidence for strong-field modifications of General Relativity. Read More

**Authors:**Daniele Trifirò

^{1}, Richard O'Shaughnessy

^{2}, Davide Gerosa

^{3}, Emanuele Berti

^{4}, Michael Kesden

^{5}, Tyson Littenberg

^{6}, Ulrich Sperhake

^{7}

**Affiliations:**

^{1}Dipartimento di Fisica E. Fermi, Università di Pisa, Italy,

^{2}Center for Computational Relativity and Gravitation, Rochester Institute of Technology, Rochester, NY, USA,

^{3}Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Cambridge, UK,

^{4}Department of Physics and Astronomy, The University of Mississippi, USA,

^{5}Department of Physics, The University of Texas at Dallas, Richardson, TX, USA,

^{6}Center for Interdisciplinary Exploration and Research in Astrophysics,

^{7}Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Cambridge, UK

Gravitational waves from coalescing binary black holes encode the evolution of their spins prior to merger. In the post-Newtonian regime and on the precession timescale, this evolution has one of three morphologies, with the spins either librating around one of two fixed points ("resonances") or circulating freely. In this work we perform full parameter estimation on resonant binaries with fixed masses and spin magnitudes, changing three parameters: a conserved "projected effective spin" $\xi$ and resonant family $\Delta\Phi=0,\pi$ (which uniquely label the source), the inclination $\theta_{JN}$ of the binary's total angular momentum with respect to the line of sight (which determines the strength of precessional effects in the waveform), and the signal amplitude. Read More

Binary black holes on quasicircular orbits with spins aligned with their orbital angular momentum have been testbeds for analytic and numerical relativity for decades, not least because symmetry ensures that such configurations are equilibrium solutions to the spin-precession equations. In this work, we show that these solutions can be unstable when the spin of the higher-mass black hole is aligned with the orbital angular momentum and the spin of the lower-mass black hole is anti-aligned. Spins in these configurations are unstable to precession to large misalignment when the binary separation $r$ is between the values $r_{\rm ud\pm}= (\sqrt{\chi_1} \pm \sqrt{q \chi_2})^4 (1-q)^{-2} M$, where $M$ is the total mass, $q \equiv m_2/m_1$ is the mass ratio, and $\chi_1$ ($\chi_2$) is the dimensionless spin of the more (less) massive black hole. Read More

The dynamics of precessing binary black holes (BBHs) in the post-Newtonian regime has a strong timescale hierarchy: the orbital timescale is very short compared to the spin-precession timescale which, in turn, is much shorter than the radiation-reaction timescale on which the orbit is shrinking due to gravitational-wave emission. We exploit this timescale hierarchy to develop a multi-scale analysis of BBH dynamics elaborating on the analysis of Kesden et al. (2015). Read More

Gravitational theories with multiple scalar fields coupled to the metric and each other --- a natural extension of the well studied single-scalar-tensor theories --- are interesting phenomenological frameworks to describe deviations from general relativity in the strong-field regime. In these theories, the $N$-tuple of scalar fields takes values in a coordinate patch of an $N$-dimensional Riemannian target-space manifold whose properties are poorly constrained by weak-field observations. Here we introduce for simplicity a non-trivial model with two scalar fields and a maximally symmetric target-space manifold. Read More

Interactions between a supermassive black hole binary and the surrounding accretion disc can both assist the binary inspiral and align the black hole spins to the disc angular momentum. While binary migration is due to angular-momentum transfer within the circumbinary disc, the spin-alignment process is driven by the mass accreting on to each black hole. Mass transfer between different disc components thus couples the inspiral and the alignment process together. Read More

**Authors:**Emanuele Berti, Enrico Barausse, Vitor Cardoso, Leonardo Gualtieri, Paolo Pani, Ulrich Sperhake, Leo C. Stein, Norbert Wex, Kent Yagi, Tessa Baker, C. P. Burgess, Flávio S. Coelho, Daniela Doneva, Antonio De Felice, Pedro G. Ferreira, Paulo C. C. Freire, James Healy, Carlos Herdeiro, Michael Horbatsch, Burkhard Kleihaus, Antoine Klein, Kostas Kokkotas, Jutta Kunz, Pablo Laguna, Ryan N. Lang, Tjonnie G. F. Li, Tyson Littenberg, Andrew Matas, Saeed Mirshekari, Hirotada Okawa, Eugen Radu, Richard O'Shaughnessy, Bangalore S. Sathyaprakash, Chris Van Den Broeck, Hans A. Winther, Helvi Witek, Mir Emad Aghili, Justin Alsing, Brett Bolen, Luca Bombelli, Sarah Caudill, Liang Chen, Juan Carlos Degollado, Ryuichi Fujita, Caixia Gao, Davide Gerosa, Saeed Kamali, Hector O. Silva, João G. Rosa, Laleh Sadeghian, Marco Sampaio, Hajime Sotani, Miguel Zilhao

One century after its formulation, Einstein's general relativity has made remarkable predictions and turned out to be compatible with all experimental tests. Most of these tests probe the theory in the weak-field regime, and there are theoretical and experimental reasons to believe that general relativity should be modified when gravitational fields are strong and spacetime curvature is large. The best astrophysical laboratories to probe strong-field gravity are black holes and neutron stars, whether isolated or in binary systems. Read More

We derive an effective potential for binary black-hole (BBH) spin precession at second post-Newtonian order. This effective potential allows us to solve the orbit-averaged spin-precession equations analytically for arbitrary mass ratios and spins. These solutions are quasiperiodic functions of time: after a fixed period the BBH spins return to their initial relative orientations and jointly precess about the total angular momentum by a fixed angle. Read More

We investigate the consequences of superkicks on the population of supermassive black holes (SMBHs) in the Universe residing in brightest cluster galaxies (BCGs). There is strong observational evidence that BCGs grew prominently at late times (up to a factor 2-4 in mass from z=1), mainly through mergers with satellite galaxies from the cluster, and they are known to host the most massive SMBHs ever observed. Those SMBHs are also expected to grow hierarchically, experiencing a series of mergers with other SMBHs brought in by merging satellites. Read More

If binary black holes form following the successive core collapses of sufficiently massive binary stars, precessional dynamics may align their spins $\mathbf S_1$ and $\mathbf S_2$ and the orbital angular momentum $\mathbf L$ into a plane in which they jointly precess about the total angular momentum $\mathbf J$. These spin orientations are known as spin-orbit resonances since $\mathbf S_1$, $\mathbf S_2$, and $\mathbf L$ all precess at the same frequency to maintain their planar configuration. Two families of such spin-orbit resonances exist, alike in dignity but differentiated by whether the components of the two spins in the orbital plane are either aligned or antialigned. Read More

We study the influence of astrophysical formation scenarios on the precessional dynamics of spinning black-hole binaries by the time they enter the observational window of second- and third-generation gravitational-wave detectors, such as Advanced LIGO/Virgo, LIGO-India, KAGRA and the Einstein Telescope. Under the plausible assumption that tidal interactions are efficient at aligning the spins of few-solar mass black-hole progenitors with the orbital angular momentum, we find that black-hole spins should be expected to preferentially lie in a plane when they become detectable by gravitational-wave interferometers. This "resonant plane" is identified by the conditions \Delta\Phi=0{\deg} or \Delta\Phi=+/-180{\deg}, where \Delta\Phi is the angle between the components of the black-hole spins in the plane orthogonal to the orbital angular momentum. Read More

**Affiliations:**

^{1}Dipartimento di Fisica, Universita' Degli Studi di Milano, Milano, Italy,

^{2}Dipartimento di Fisica, Universita' Degli Studi di Milano, Milano, Italy

In this Letter we revisit arguments suggesting that the Bardeen-Petterson effect can coalign the spins of a central supermassive black hole binary accreting from a circumbinary (or circumnuclear) gas disc. We improve on previous estimates by adding the dependence on system parameters, and noting that the nonlinear nature of warp propagation in a thin viscous disc affects alignment. This reduces the disc's ability to communicate the warp, and can severely reduce the effectiveness of disc-assisted spin alignment. Read More