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General Relativity and Quantum Cosmology (gr-qc)

Mon, 17 Apr 2023

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1.Nonlinearly scalarized rotating black holes in Einstein-scalar-Gauss-Bonnet theory

Authors:Meng-Yun Lai, De-Cheng Zou, Rui-Hong Yue, Yun Soo Myung

Abstract: In this paper, we discuss a fully nonlinear mechanism for the formation of scalarized rotating black holes in EsGB gravity, where Kerr black holes are linearly stable, but unstable against nonlinear scalar perturbations. With the help of pseudo spectral method, we obtain the solutions of nonlinearly scalarized rotating black holes, and find a complicated spectrum of these black holes solutions with multiple scalarized branches. Moreover, we investigate the thermodynamic properties of nonlinearly scalarized rotating black holes and find the phase transition between Kerr and these black holes.

2.Hybrid Proca-boson stars

Authors:Tian-Xiang Ma, Chen Liang, Jie Yang, Yong-Qiang Wang

Abstract: In this paper, we construct a hybrid boson star model that contains a complex scalar field and a Proca field. The scalar field is in the ground state, while the Proca field is in the first excited state. We numerically solve the model and obtain solution families of different coexisting states by considering both synchronized and nonsynchronized cases. By examining the relation between ADM mass and synchronized frequency $\tilde{\omega}$ or nonsynchronized frequency $\tilde{\omega}_P$, we identify several types of solution families for the hybrid boson stars. In addition to solutions that intersect the scalar field and the Proca field at each end, there are also several types of multi-branch coexisting state solutions. The characteristics of various solutions are analyzed and discussed in detail. We calculate the binding energy $E$ of the hybrid Proca-boson stars and provide the relationship between $E$ and both synchronized frequency $\tilde{\omega}$ and nonsynchronized frequency $\tilde{\omega}_P$. Furthermore, we obtain the stability of the corresponding hybrid star solution families from these analyses above.

3.On the extended thermodynamics of the bumblebee black holes

Authors:Zhan-Feng Mai, Rui Xu, Dicong Liang, Lijing Shao

Abstract: As a vector-tensor theory including nonminimal coupling between the Ricci tensor and a vector field, the bumblebee gravity is a potential theory to test Lorentz symmetry violation. Recently, a new class of numerical spherical black holes in the bumblebee theory was constructed. In this paper, we investigate the associated local thermodynamic properties. By introducing a pair of conjugated thermodynamic quantities $X$ and $Y$, which can be interpreted as an extension of electric potential and charge of the Reissner Nordstr\"om black holes, we numerically construct a new first law of thermodynamics for bumblebee black holes. We then study the constant-$Y$ processes in the entropy-charge parameter space. For the constant-$Y$ processes, we also calculate the heat capacity to study the local thermodynamic stability of the bumblebee black holes. For a negative nonminimal coupling coefficient $\xi$, we find both divergent and smooth phase transitions. For a positive but small $\xi$, only a divergent phase transition is found. It turns out that there is a critical value $0.4\kappa <\xi_c < 0.5\kappa$ such that when $\xi_c < \xi<2\kappa$, even the divergent phase transition disappears and the bumblebee black holes thus become locally thermodynamically unstable regardless of the bumblebee charge. As for $\xi>2\kappa$, the smooth phase transition arises again but there no longer exists any discontinuous phase transition for the bumblebee black holes.

4.Non-parametric inference of the population of compact binaries from gravitational wave observations using binned Gaussian processes

Authors:Anarya Ray, Ignacio Magaña Hernandez, Siddharth Mohite, Jolien Creighton, Shasvath Kapadia

Abstract: The observation of gravitational waves from multiple compact binary coalescences by the LIGO-Virgo-KAGRA detector networks has enabled us to infer the underlying distribution of compact binaries across a wide range of masses, spins, and redshifts. In light of the new features found in the mass spectrum of binary black holes and the uncertainty regarding binary formation models, non-parametric population inference has become increasingly popular. In this work, we develop a data-driven clustering framework that can identify features in the component mass distribution of compact binaries simultaneously with those in the corresponding redshift distribution, from gravitational wave data in the presence of significant measurement uncertainties, while making very few assumptions on the functional form of these distributions. Our generalized model is capable of inferring correlations among various population properties such as the redshift evolution of the shape of the mass distribution itself, in contrast to most existing non-parametric inference schemes. We test our model on simulated data and demonstrate the accuracy with which it can re-construct the underlying distributions of component masses and redshifts. We also re-analyze public LIGO-Virgo-KAGRA data from events in GWTC-3 using our model and compare our results with those from some alternative parametric and non-parametric population inference approaches. Finally, we investigate the potential presence of correlations between mass and redshift in the population of binary black holes in GWTC-3 (those observed by the LIGO-Virgo-KAGRA detector network in their first 3 observing runs), without making any assumptions about the specific nature of these correlations.

5.Nonlinear instability and scalar clouds of spherical exotic compact objects in scalar-Gauss-Bonnet theory

Authors:Shao-Jun Zhang

Abstract: In this work, we present a new type of scalar clouds supported by spherically symmetric horizonless compact objects in the scalar-Gauss-Bonnet theory. Unlike the previous spontaneous scalarization that is triggered by the tachyonic instability, our scalarization arises from a nonlinear instability that is non-spontaneous. We explore two types of boundary conditions for the scalar field at the surface of the compact objects and find an infinite countable set of scalar clouds characterized by the number of nodes for both cases. Our study demonstrates that boundary conditions have a significant impact on the formation of scalar clouds. Specifically, for the Dirichlet boundary condition, scalarization is more likely to occur for compact objects with medium radii and becomes harder for ultra-compact and large ones. Conversely, for the Robin boundary condition, scalarization is easier for more compact objects.

6.Strong Gravitational Lensing in Horndeski theory

Authors:Pedro Bessa

Abstract: In this paper we build the general formalism of gravitational lensing in luminal Horndeski theories, deriving the Jacobi matrix equation and the general angular diameter distance in these theories through the screen space formalism. We generalize the focusing and multiple lensing theorems to include Scalar Tensor theories belonging to the class and derive constraints they must satisfy to exhibit the same gravitional lensing behavior predicted by General Relativity. This provides a way to test theories through Strong Lensing effects, as well as a full theoretical framework for testing lensing in these theories. We find that for some subclasses, like metric $f(R)$ and unified $k$-essence, the conditions are satisified in general physical cases, while for others like Galileon Condensate models, the conditions impose constraints on the parameter space of the theory.

7.Search for Postmerger Gravitational Waves from Binary Neutron Star Mergers Using a Matched-filtering Statistic

Authors:Andrzej Królak, Piotr Jaranowski, Michał Bejger, Paweł Ciecieląg, Orest Dorosh, Andrzej Pisarski

Abstract: In this paper, we present a new method to search for a short postmerger gravitational-wave signal following the merger of two neutron stars. Such a signal could follow the event GW170817 observed by LIGO and Virgo detectors. Our method is based on a matched filtering statistic and an approximate template of the postmerger signal in the form of a damped sinusoid. We test and validate our method using postmerger numerical simulations from the CoRe database. We find no evidence of the short postmerger signal in the LIGO data following the GW170817 event and we obtain upper limits. For short postmerger signals investigated, our best upper limit on the root sum square of the gravitational-wave strain emitted from 1.15 kHz to 4 kHz is $h_{\text{rss}}^{50\%}=1.8\times 10^{-22}/\sqrt{\text{Hz}}$ at 50% detection efficiency. The distance corresponding to this best upper limit is 4.64 Mpc.

8.Fermi equation of state with finite temperature corrections in quantum space-times approach: Snyder model case

Authors:Anna Pachoł, Aneta Wojnar

Abstract: We investigate the impact of the deformed phase space associated with the quantum Snyder space on microphysical systems. The general Fermi-Dirac equation of state and specific corrections to it are derived. We put emphasis on non-relativistic degenerate Fermi gas as well as on the temperature-finite corrections to it. Considering the most general one-parameter family of deformed phase spaces associated with the Snyder model allows us to study whether the modifications arising in physical effects depend on the choice of realization. It turns out that we can distinguish three different cases with radically different physical consequences.

9.Unifying inflation with early and late dark energy in Einstein-Gauss-Bonnet gravity

Authors:Shin'ichi Nojiri, Sergei D. Odintsov, Diego Sáez-Chillón Gómez

Abstract: In the era of precision cosmology, different observational data has led to precise measurements of the Hubble constant that differ significantly, what has been called the Hubble tension problem. In order to solve such a discrepancy, many different solutions have been proposed, from systematic errors on the observational data to theoretical proposals that assume an early dark energy that might affect the universe expansion at the time of recombination. In this paper, a model of varying cosmological constant is proposed in the framework of Einstein-Gauss-Bonnet gravity. The corresponding gravitational action is reconstructed and such a model is shown to reproduce well the inflationary era together with dark energy epoch and at the same time to provide an explanation for the discrepancy on the Hubble constant predictions. The transition to a phantom epoch is also realised, avoiding the usual instability problems of ordinary scalar field models.

10.Controlled regularity at future null infinity from past asymptotic initial data: massless fields

Authors:Grigalius Taujanskas, Juan A. Valiente Kroon

Abstract: We study the relation between asymptotic characteristic initial data at past null infinity for the massless linear spin-s field equations and the regularity of the solutions at future null infinity. We quantitatively control the solutions to the spin-s equations on a causal rectangle reaching spatial infinity and containing portions of past and future null infinity. As a consequence, we show that even linear fields generically acquire polyhomogeneous expansions near future null infinity, with the regularity of the terms controlled precisely in terms of the regularity of the past characteristic initial data. Our analysis makes use of Friedrich's representation of spatial infinity together with a careful Gr\"onwall-type estimate that does not degenerate at the critical sets where null infinity meets spatial infinity, and Luk's strategy for the construction of optimal existence domains for the characteristic initial value problem.

11.LISAmax: Improving the Gravitational-Wave Sensitivity by Two Orders of Magnitude

Authors:Waldemar Martens, Michael Khan, Jean-Baptiste Bayle

Abstract: Within its Voyage 2050 planning cycle, the European Space Agency (ESA) is considering long-term large class science mission themes. Gravitational-wave astronomy is among the topics under study. This paper presents "LISAmax", a gravitational-wave interferometer concept consisting of three spacecraft located close to the Sun-Earth libration points L3, L4 and L5, forming a triangular constellation with an arm length of 259 million kilometers (to be compared to LISA's 2.5 million kilometer arms). This is the largest triangular formation that can be reached from Earth without a major leap in mission complexity and cost. The sensitivity curve of such a detector is at least two orders of magnitude lower in amplitude than that of LISA. Depending on the choice of other instrument parameters, this makes the detector sensitive to gravitational waves in the micro-Hertz range and opens a new window for gravitational-wave astronomy, not covered by any other planned detector concept. We analyze in detail the constellation stability for a 10-year mission in the full numerical model and compute the orbit transfers using a European launcher and chemical propulsion. The payload design parameters are assessed, and the expected sensitivity curve is compared with a number of potential gravitational-wave sources. No show stoppers are identified at this point of the analysis.

12.Exploring the multi-band gravitational wave background with a semi-analytic galaxy formation model

Authors:Zhencheng Li, Zhen Jiang, Xi-Long Fan, Yun Chen, Liang Gao, Shenghua Yu

Abstract: The compact binary systems, spanning from the stellar to supermassive black hole, encode a wealth of information concerning stellar evolution, galaxy formation and evolution, and cosmology. An enormous number of these systems, both resolved and unresolved, emit substantial gravitational waves during their final evolutionary stages, thereby creating a stochastic gravitational wave background (SGWB). We calculate the merger rates of stellar compact binaries and massive black hole binaries using a semi-analytic galaxy formation model -- Galaxy Assembly with Binary Evolution (GABE) in a unified and self-consistent approach, followed by an estimation of the multi-band SGWB contributed by the binary systems. We find that the amplitudes of the principal peaks of the SGWB energy density are within one order of magnitude $\Omega_{GW} \sim 10^{-9}- 10^{-8}$. This SGWB can be easily detected by the Square Kilometre Array (SKA), as well as planned interferometric detectors, such as the Einstein Telescope (ET) and the Laser Interferometer Space Antenna (LISA). The energy density of this background varies as $\Omega_{GW} \propto f^{2/3}$ in the SKA band. The shape of the SGWB spectrum in the frequency range $\sim[10^{-4}$,$1]$Hz could allow the space-based detector LISA to distinguish the black hole seed models. The amplitude of the SGWB from merging stellar binary black holes (BBHs) at $\sim 100$ Hz is approximately 10 and 100 times greater than those from merging binary neutron stars (BNSs) and neutron-star-black-hole (NSBH) mergers, respectively.

13.Insight into the Microstructure of FRW Universe from a $P$-$v$ Phase Transition

Authors:Haximjan Abdusattar

Abstract: The $P$-$v$ phase transition of the FRW (Friedmann-Robertson-Walker) universe with a perfect fluid has recently been investigated, revealing that the four critical exponents near the critical point are consistent with the values predicted by mean field theory. Notably, the coexistence phase of the $P$-$v$ phase transition in the FRW universe above the critical temperature, which distinguishes it from van der Waals system and most of AdS black holes system. This unique property allows us to investigate the microstructure of the FRW universe as a thermodynamic system. Our analysis of the Ruppeiner thermodynamic geometry for the FRW universe reveals that the behavior of the scalar curvature near criticality is characterized by a dimensionless constant identical to that of the van der Waals fluid. Additionally, we observe that while repulsive interactions dominate for the coexistence large phase with higher temperature, the scalar curvature for the coexistence small phase is always negative, indicating attractive interactions, providing new insights into the nature of interactions among the perfect fluid matter constituents in the expanding FRW universe.

14.Covariant spin-parity decomposition of the Torsion and Path Integrals

Authors:Riccardo Martini, Gregorio Paci, Dario Sauro

Abstract: We propose a functional measure over the torsion tensor. We discuss two completely equivalent choices for the Wheeler-DeWitt supermetric for this field, the first one being based on its algebraic decomposition, the other inspired by teleparallel theories of gravity. The measure is formally defined by requiring the normalization of the Gaussian integral. To achieve such a result we split the torsion tensor into its spin-parity eigenstates by constructing a new, York-like, decomposition. Of course, such a decomposition has a wider range of applicability to any kind of tensor sharing the symmetries of the torsion. As a result of this procedure a functional Jacobian naturally arises, whose formal expression is given exactly in the phenomenologically interesting limit of maximally symmetric spaces. We also discuss the explicit computation of this Jacobian in the case of a $4$-dimensional sphere $S^4$ with particular emphasis on its logarithmic divergences.

15.Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Authors:The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, R. Abbott, H. Abe, F. Acernese, K. Ackley, S. Adhicary, N. Adhikari, R. X. Adhikari, V. K. Adkins, V. B. Adya, C. Affeldt, D. Agarwal, M. Agathos, O. D. Aguiar, L. Aiello, A. Ain, P. Ajith, T. Akutsu, S. Albanesi, R. A. Alfaidi, C. Alléné, A. Allocca, P. A. Altin, A. Amato, S. Anand, A. Ananyeva, S. B. Anderson, W. G. Anderson, M. Ando, T. Andrade, N. Andres, M. Andrés-Carcasona, T. Andrić, S. Ansoldi, J. M. Antelis, S. Antier, T. Apostolatos, E. Z. Appavuravther, S. Appert, S. K. Apple, K. Arai, A. Araya, M. C. Araya, J. S. Areeda, M. Arène, N. Aritomi, N. Arnaud, M. Arogeti, S. M. Aronson, H. Asada, G. Ashton, Y. Aso, M. Assiduo, S. Assis de Souza Melo, S. M. Aston, P. Astone, F. Aubin, K. AultONeal, S. Babak, F. Badaracco, C. Badger, S. Bae, Y. Bae, S. Bagnasco, Y. Bai, J. G. Baier, J. Baird, R. Bajpai, T. Baka, M. Ball, G. Ballardin, S. W. Ballmer, G. Baltus, S. Banagiri, B. Banerjee, D. Bankar, J. C. Barayoga, B. C. Barish, D. Barker, P. Barneo, F. Barone, B. Barr, L. Barsotti, M. Barsuglia, D. Barta, J. Bartlett, M. A. Barton, I. Bartos, S. Basak, R. Bassiri, A. Basti, M. Bawaj, J. C. Bayley, M. Bazzan, B. Bécsy, V. M. Bedakihale, F. Beirnaert, M. Bejger, I. Belahcene, A. S. Bell, V. Benedetto, D. Beniwal, W. Benoit, J. D. Bentley, M. BenYaala, S. Bera, M. Berbel, F. Bergamin, B. K. Berger, S. Bernuzzi, M. Beroiz, C. P. L. Berry, D. Bersanetti, A. Bertolini, J. Betzwieser, D. Beveridge, R. Bhandare, A. V. Bhandari, U. Bhardwaj, R. Bhatt, D. Bhattacharjee, S. Bhaumik, A. Bianchi, I. A. Bilenko, M. Bilicki, G. Billingsley, S. Bini, O. Birnholtz, S. Biscans, M. Bischi, S. Biscoveanu, A. Bisht, B. Biswas, M. Bitossi, M. -A. Bizouard, J. K. Blackburn, C. D. Blair, D. G. Blair, R. M. Blair, F. Bobba, N. Bode, M. Boër, G. Bogaert, M. Boldrini, G. N. Bolingbroke, L. D. Bonavena, R. Bondarescu, F. Bondu, E. Bonilla, R. Bonnand, P. Booker, R. Bork, V. Boschi, N. Bose, S. Bose, V. Bossilkov, V. Boudart, Y. Bouffanais, A. Bozzi, C. Bradaschia, P. R. Brady, A. Bramley, A. Branch, M. Branchesi, J. E. Brau, M. Breschi, T. Briant, J. H. Briggs, A. Brillet, M. Brinkmann, P. Brockill, A. F. Brooks, J. Brooks, D. D. Brown, S. Brunett, G. Bruno, R. Bruntz, J. Bryant, F. Bucci, J. Buchanan, T. Bulik, H. J. Bulten, A. Buonanno, K. Burtnyk, R. Buscicchio, D. Buskulic, C. Buy, R. L. Byer, G. S. Cabourn Davies, G. Cabras, R. Cabrita, L. Cadonati, G. Cagnoli, C. Cahillane, J. Calderón Bustillo, J. D. Callaghan, T. A. Callister, E. Calloni, J. B. Camp, M. Canepa, G. Caneva, M. Cannavacciuolo, K. C. Cannon, H. Cao, Z. Cao, L. A. Capistran, E. Capocasa, E. Capote, G. Carapella, F. Carbognani, M. Carlassara, J. B. Carlin, M. Carpinelli, G. Carrillo, J. J. Carter, G. Carullo, J. Casanueva Diaz, C. Casentini, G. Castaldi, S. Caudill, M. Cavaglià, F. Cavalier, R. Cavalieri, G. Cella, P. Cerdá-Durán, E. Cesarini, W. Chaibi, W. Chakalis, S. Chalathadka Subrahmanya, E. Champion, C. -H. Chan, C. Chan, C. L. Chan, K. Chan, M. Chan, K. Chandra, I. P. Chang, W. Chang, P. Chanial, S. Chao, C. Chapman-Bird, P. Charlton, E. Chassande-Mottin, C. Chatterjee, Debarati Chatterjee, Deep Chatterjee, M. Chaturvedi, S. Chaty, K. Chatziioannou, C. Chen, D. Chen, H. Y. Chen, J. Chen, K. Chen, X. Chen, Y. -B. Chen, Y. -R. Chen, Y. Chen, H. Cheng, P. Chessa, H. Y. Cheung, H. Y. Chia, F. Chiadini, C-Y. Chiang, G. Chiarini, R. Chierici, A. Chincarini, M. L. Chiofalo, A. Chiummo, R. K. Choudhary, S. Choudhary, N. Christensen, Q. Chu, Y-K. Chu, S. S. Y. Chua, K. W. Chung, G. Ciani, P. Ciecielag, M. Cieślar, M. Cifaldi, A. A. Ciobanu, R. Ciolfi, F. Clara, J. A. Clark, T. A. Clarke, P. Clearwater, S. Clesse, F. Cleva, E. Coccia, E. Codazzo, P. -F. Cohadon, D. E. Cohen, M. Colleoni, C. G. Collette, A. Colombo, M. Colpi, C. M. Compton, L. Conti, S. J. Cooper, P. Corban, T. R. Corbitt, I. Cordero-Carrión, S. Corezzi, N. J. Cornish, A. Corsi, S. Cortese, A. C. Coschizza, R. Cotesta, R. Cottingham, M. W. Coughlin, J. -P. Coulon, S. T. Countryman, B. Cousins, P. Couvares, D. M. Coward, M. J. Cowart, D. C. Coyne, R. Coyne, K. Craig, J. D. E. Creighton, T. D. Creighton, A. W. Criswell, M. Croquette, S. G. Crowder, J. R. Cudell, T. J. Cullen, A. Cumming, R. Cummings, E. Cuoco, M. Curyło, P. Dabadie, T. Dal Canton, S. Dall'Osso, G. Dálya, A. Dana, B. D'Angelo, S. Danilishin, S. D'Antonio, K. Danzmann, C. Darsow-Fromm, A. Dasgupta, L. E. H. Datrier, Sayak Datta, Sayantani Datta, V. Dattilo, I. Dave, M. Davier, D. Davis, M. C. Davis, E. J. Daw, M. Dax, D. DeBra, M. Deenadayalan, J. Degallaix, M. De Laurentis, S. Deléglise, V. Del Favero, F. De Lillo, N. De Lillo, D. Dell'Aquila, W. Del Pozzo, F. De Matteis, V. D'Emilio, N. Demos, T. Dent, A. Depasse, R. De Pietri, R. De Rosa, C. De Rossi, R. DeSalvo, R. De Simone, S. Dhurandhar, R. Diab, M. C. Díaz, N. A. Didio, T. Dietrich, L. Di Fiore, C. Di Fronzo, C. Di Giorgio, F. Di Giovanni, M. Di Giovanni, T. Di Girolamo, D. Diksha, A. Di Lieto, A. Di Michele, S. Di Pace, I. Di Palma, F. Di Renzo, A. K. Divakarla, A. Dmitriev, Z. Doctor, P. P. Doleva, L. Donahue, L. D'Onofrio, F. Donovan, K. L. Dooley, T. Dooney, S. Doravari, O. Dorosh, M. Drago, J. C. Driggers, Y. Drori, J. -G. Ducoin, L. Dunn, U. Dupletsa, O. Durante, D. D'Urso, P. -A. Duverne, S. E. Dwyer, C. Eassa, P. J. Easter, M. Ebersold, T. Eckhardt, G. Eddolls, B. Edelman, T. B. Edo, O. Edy, A. Effler, S. Eguchi, J. Eichholz, S. S. Eikenberry, M. Eisenmann, R. A. Eisenstein, A. Ejlli, E. Engelby, Y. Enomoto, L. Errico, R. C. Essick, H. Estellés, D. Estevez, T. Etzel, M. Evans, T. M. Evans, T. Evstafyeva, B. E. Ewing, J. M. Ezquiaga, F. Fabrizi, F. Faedi, V. Fafone, H. Fair, S. Fairhurst, P. C. Fan, A. M. Farah, B. Farr, W. M. Farr, G. Favaro, M. Favata, M. Fays, M. Fazio, J. Feicht, M. M. Fejer, E. Fenyvesi, D. L. Ferguson, A. Fernandez-Galiana, I. Ferrante, T. A. Ferreira, F. Fidecaro, P. Figura, A. Fiori, I. Fiori, M. Fishbach, R. P. Fisher, R. Fittipaldi, V. Fiumara, R. Flaminio, E. Floden, H. K. Fong, J. A. Font, B. Fornal, P. W. F. Forsyth, A. Franke, S. Frasca, F. Frasconi, J. P. Freed, Z. Frei, A. Freise, O. Freitas, R. Frey, P. Fritschel, V. V. Frolov, G. G. Fronzé, Y. Fujii, Y. Fujikawa, Y. Fujimoto, P. Fulda, M. Fyffe, H. A. Gabbard, W. E. Gabella, B. U. Gadre, J. R. Gair, J. Gais, S. Galaudage, R. Gamba, D. Ganapathy, A. Ganguly, D. -F. Gao, D. Gao, S. G. Gaonkar, B. Garaventa, C. García-Núñez, C. García-Quirós, K. A. Gardner, J. Gargiulo, F. Garufi, C. Gasbarra, B. Gateley, V. Gayathri, G. -G. Ge, G. Gemme, A. Gennai, J. George, O. Gerberding, L. Gergely, S. Ghonge, Abhirup Ghosh, Archisman Ghosh, Shaon Ghosh, Shrobana Ghosh, Tathagata Ghosh, L. Giacoppo, J. A. Giaime, K. D. Giardina, D. R. Gibson, C. Gier, P. Giri, F. Gissi, S. Gkaitatzis, J. Glanzer, A. E. Gleckl, F. G. Godoy, P. Godwin, E. Goetz, R. Goetz, J. Golomb, B. Goncharov, G. González, M. Gosselin, R. Gouaty, D. W. Gould, S. 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Abstract: Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects.

16.Event horizon gluing and black hole formation in vacuum: the very slowly rotating case

Authors:Christoph Kehle, Ryan Unger

Abstract: In this paper, we initiate the study of characteristic event horizon gluing in vacuum. More precisely, we prove that Minkowski space can be glued along a null hypersurface to any round symmetry sphere in a Schwarzschild black hole spacetime as a $C^2$ solution of the Einstein vacuum equations. The method of proof is fundamentally nonperturbative and is closely related to our previous work in spherical symmetry [KU22] and Christodoulou's short pulse method [Chr09]. We also make essential use of the perturbative characteristic gluing results of Aretakis-Czimek-Rodnianski [ACR21a; CR22]. As an immediate corollary of our methods, we obtain characteristic gluing of Minkowski space to the event horizon of very slowly rotating Kerr with prescribed mass $M$ and specific angular momentum $a$. Using our characteristic gluing results, we construct examples of vacuum gravitational collapse to very slowly rotating Kerr black holes in finite advanced time with prescribed $M$ and $0\le |a|\ll M$. Our construction also yields the first example of a spacelike singularity arising from one-ended, asymptotically flat gravitational collapse in vacuum.

17.A stationary axisymmetric vacuum solution for pure $R^2$ gravity

Authors:Mustapha Azreg-Aïnou, Hoang Ky Nguyen

Abstract: The closed-form expression for pure $R^2$ vacuum solution obtained in arXiv:2211.03542 [gr-qc] (to appear in Phys. Rev. D) lends itself to a generalization to axisymmetric setup via the modified Newman-Janis algorithm. We adopt the procedure put forth in Phys. Rev. D 90, 064041 (2014) bypassing the complexification of the radial coordinate. The procedure presumes the existence of Boyer-Lindquist coordinates. Using the Event Horizon Telescope Collaboration results, we model the central black hole M87* by the thus obtained exact rotating metric, depending on the mass, rotation parameter and a third dimensionless parameter. The latter is constrained upon investigating the shadow angular size assuming mass and rotation parameters are those of M87*.