2023-1201

• [2311.18640] The detection, extraction and parameter estimation of extreme-mass-ratio inspirals with deep learning
Abstract: One of the primary goals of space-borne gravitational wave detectors is to detect and analyze extreme-mass-ratio inspirals (EMRIs). This endeavor presents a significant challenge due to the complex and lengthy EMRI signals, further compounded by their inherently faint nature. In this letter, we introduce a 2-layer Convolutional Neural Network (CNN) approach to detect EMRI signals for space-borne detectors, achieving a true positive rate (TPR) of 96.9 % at a 1 % false positive rate (FPR) for signal-to-noise ratio (SNR) from 50 to 100. Especially, the key intrinsic parameters of EMRIs such as mass and spin of the supermassive black hole (SMBH) and the initial eccentricity of the orbit can be inferred directly by employing a VGG network. The mass and spin of the SMBH can be determined at 99 % and 92 % respectively. This will greatly reduce the parameter spaces and computing cost for the following Bayesian parameter estimation. Our model also has a low dependency on the accuracy of the waveform model. This study underscores the potential of deep learning methods in EMRI data analysis, enabling the rapid detection of EMRI signals and efficient parameter estimation.

Keywords: EMRI; GW; AI

2023-1206

• [2312.02889] Propagation of Gravitational Waves in a Dynamical Wormhole Background for Two-scalar Einstein-Gauss-Bonnet Theory
Abstract: In this work, we propose a model of Einstein--Gauss-Bonnet gravity coupled with two scalar fields. The two scalar fields are considered to be ``frozen'' or they become non-dynamical by employing appropriate constraints in terms of Lagrange multiplier fields. We show that, even in the case that the arbitrary spherically symmetric spacetime is dynamical, we can construct a model where the wormhole spacetime is a stable solution in this framework. We especially concentrate on the model reproducing the dynamical wormhole, where the wormhole appears in a finite-time interval. We investigate the propagation of the gravitational wave in the wormhole spacetime background and we show that the propagation speed is different from that of light → light in general, and there is a difference in the speeds between the incoming propagating wave and the outgoing propagating gravitational wave.

Keywords: GW; wormhole

2023-1207

• [2312.03191] Can we distinguish black holes with electric and magnetic charges from quasinormal modes?
Abstract: We compute the quasinormal modes of static and spherically symmetric black holes (BHs) with electric and magnetic charges. For the electrically charged case, the dynamics of perturbations separates into the odd- and even-parity sectors with two coupled differential equations in each sector. In the presence of both electric and magnetic charges, the differential equations of four dynamical degrees of freedom are coupled with each other between odd- and even-parity perturbations. Despite this notable modification, we show that, for a given total charge and mass, a BH with mixed electric and magnetic charges gives rise to the same quasinormal frequencies for fundamental modes. This includes the case in which two BHs have equal electric and magnetic charges for each of them. Thus, the gravitational-wave observations of quasinormal modes during the ringdown phase alone do not distinguish between electrically and magnetically charged BHs.

Keywords: QNM; electric charge; magnetic charge; BH

2023-1213

• [2312.06767] Axion Weak Leaks: extreme mass-ratio inspirals in ultra-light dark matter
Abstract: Previous works have argued that future gravitational-wave detectors will be able to probe the properties of astrophysical environments where binary coalesce, including accretion disks, but also dark matter structures. Most analyses have resorted to a Newtonian modelling of the environmental effects, which are not suited to study extreme-mass-ratio inspirals immersed in structures of ultra-light bosons. In this letter, we use relativistic perturbation theory to consistently study these systems in spherical symmetry. We compute the flux of scalar particles and the rate at which orbital energy (and angular momentum) is dissipated via gravitational radiation and depletion of scalars, i.e. dynamical friction. Our results suggest that the Laser Inteferometer Space Antenna will be able to probe ultra-light dark matter structures in the Galaxy by tracking the phase of extreme-mass-ratio inspirals.

Keywords: EMRI; dark matter

• [2312.07461] Baryon-induced collapse of dark matter cores into supermassive black holes
Abstract: Non-linear structure formation for fermionic dark matter particles leads to dark matter density profiles with a degenerate compact core surrounded by a diluted halo. For a given fermion mass, the core has a critical mass that collapses into a supermassive black hole (SMBH). Galactic dynamics constraints suggest  fermion, which leads to  critical core mass. Here, we show that baryonic (ordinary) matter accretion drives an initially stable dark matter core to SMBH formation and determine the accreted mass threshold that induces it. Baryonic gas density ρb and velocity vb inferred from cosmological hydro-simulations and observations produce sub-Eddington accretion rates triggering the baryon-induced collapse in less than a Gyr. This process produces active galactic nuclei in galaxy mergers and the high-redshift Universe. For TXS 2116-077, merging with a nearby galaxy, the observed  SMBH, for , forms in ≈0.6 Gyr, consistent with the 0.5-2 Gyr merger timescale and younger jet. For the farthest central SMBH detected by the \textit{Chandra} X-ray satellite in the z=10.3 UHZ1 galaxy observed by the James Webb Space Telescope (\textit{JWST}), the mechanism leads to a  SMBH in 87-187 Myr, starting the accretion at z=12-15. The baryon-induced collapse can also explain the  SMBHs revealed by the JWST at z≈4-6. After its formation, the SMBH can grow to a few  in timescales shorter than a Gyr via sub-Eddington baryonic mass accretion.

Keywords: dark matter

2023-1215

• [2312.08435] Spectral method for metric perturbations of black holes: Kerr background case in general relativity
Abstract: We present a novel approach, Metric pErTuRbations wIth speCtral methodS (METRICS), to calculate the gravitational metric perturbations and the quasinormal-mode frequencies of rotating black holes of any spin without decoupling the linearized field equations. We demonstrate the method by applying it to perturbations of Kerr black holes of any spin, simultaneously solving all ten linearized Einstein equations in the Regge-Wheeler gauge through purely algebraic methods and computing the fundamental (co-rotating) quadrupole mode frequency at various spins. We moreover show that the METRICS approach is accurate and precise, yielding (i) quasinormal mode frequencies that agree with Leaver's, continuous-fraction solution with a relative fractional error smaller than 10−5 for all dimensionless spins below up to 0.95, and (ii) metric perturbations that lead to Teukolsky functions that also agree with Leaver's solution with mismatches below 1% for all spins below 0.9. By not requiring the decoupling or the angular separation of the linearized field equations, the METRICS approach has the potential to be straightforwardly adapted for the computation of the quasinormal-mode frequencies of rotating black holes of any spin beyond general relativity or in the presence of matter.

Keywords: metric perturbation; QNM