arXiv subjects

Jian-dong Zhang

Publications and source records attributed to Jian-dong Zhang.

At least 19 recordsLinked to original sources

arXiv2026

A Deep Learning Framework for Amplitude Generation of Generic EMRIs

One of the main targets for space-borne gravitational wave detectors is the detection of Extreme Mass Ratio Inspirals(EMRIs). Data analysis of EMRIs requires waveform models that are both accurate and fast. The major challenge for the fast generation of such waveforms is the generation of the Teukolsky amplitudes for generic (eccentric and inclined) Kerr orbits. The requirement for modeling ${\sim 10^5}$ harmonic modes in a four-dimensional parameter space makes traditional approaches, including direct computation or dense interpolation, computationally prohibitive. To overcome this issue, we introduce a convolutional encoder-decoder architecture for a fast and end-to-end global fitting of the Teukolsky amplitudes. We also adopt a transfer learning strategy to reduce the size of the training dataset, and the model is gradually trained from the simplest Schwarzschild circular orbits to generic Kerr orbits step by step. Within this framework, we obtain a surrogate model based on a semi-analytical Post-Newtonian dataset, and the full harmonic amplitudes can be generated within milliseconds, while the median mode-distribution error for generic orbits is $\sim 10^{-3}$. This result indicates that the framework is viable for the construction of efficient waveform models for EMRIs.

gr-qc↗

arXiv2026

Gravitational Wave Astronomy With TianQin

The opening of the gravitational wave window has significantly enhanced our capacity to explore the universe's most extreme and dynamic sector. In the mHz frequency range, a diverse range of compact objects, from the most massive black holes at the farthest reaches of the Universe to the lightest white dwarfs in our cosmic backyard, generate a complex and dynamic symphony of gravitational wave signals. Once recorded by gravitational wave detectors, these unique fingerprints have the potential to decipher the birth and growth of cosmic structures over a wide range of scales, from stellar binaries and stellar clusters to galaxies and large-scale structures. The TianQin space-borne gravitational wave mission is scheduled for launch in the 2030s, with an operational lifespan of five years. It will facilitate pivotal insights into the history of our universe. This document presents a concise overview of the detectable sources of TianQin, outlining their characteristics, the challenges they present, and the expected impact of the TianQin observatory on our understanding of them.

astro-ph.GA↗

arXiv2026

Fundamental Physics and Cosmology with TianQin

The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the future? These are the basic questions that press for answers. The space-based gravitational wave detector TianQin will tune in to gravitational waves in the millihertz frequency range ($10^{-4} \sim 1$ Hz, to be specific), opening a new gravitational wave spectrum window to explore many of the previously hidden sectors of the universe. TianQin will discover many astrophysical systems, populating the universe at different redshifts: some will be of new types that have never been detected before, some will have very high signal-to-noise ratios, and some will have very high parameter estimation precision. The plethora of information collected will bring us to new fronts on which to search for the breaking points of general relativity, the possible violation of established physical laws, the signature of possible new gravitational physics and new fundamental fields, and to improve our knowledge on the expansion history of the universe. In this white paper, we highlight the advances that TianQin can bring to fundamental physics and cosmology.

gr-qc↗

arXiv2026

Bayesian model selection of Primordial Black Holes and Dressed Primordial Black Holes with lensed Gravitational Waves

If particle dark matter (DM) and primordial black holes (PBHs) coexist, PBHs will be surrounded by particle DM, forming celestial objects known as dressed PBHs (dPBHs). These structures suggest a scenario in which PBHs and DM can exist simultaneously. However, in the high-frequency regime, the gravitational lensing effect of bare PBHs is similar to that of dPBHs. Ground-based gravitational wave (GW) detectors are particularly sensitive to high-frequency GW signals. In this regime, the lensing effect of a point-mass lens with a mass in the range of $10^{-1} \sim 10^2 M_{\odot}$ becomes significant. In this work, we incorporate dPBH models with GW observations and employ Bayesian inference techniques to distinguish PBHs from dPBHs. Using the third-generation ground-based GW detectors, Einstein Telescope (ET) and Cosmic Explorer (CE), as examples, we demonstrate that these detectors can effectively differentiate the lensing effects of dPBHs from those of PBHs across a broad frequency range. Furthermore, we find that with a larger black hole (BH) mass inside the surrounding particle DM, ET and CE can distinguish these two lensed models with even greater precision.

gr-qc↗

arXiv2025

Mapping Anisotropies in the Stochastic Gravitational-Wave Background with space detector networks

Future space-based gravitational-wave detectors such as TianQin, LISA, and Taiji are expected to conduct joint observations. Such a multi-detector network will provide complementary viewing angles for the anisotropic stochastic gravitational-wave background (SGWB), thereby significantly enhancing the capability to reconstruct and localize its spatial distribution. In this paper, we have established the first dedicated data analysis pipeline for the anisotropic stochastic gravitational-wave background using a joint network of TianQin, LISA, and Taiji. Our analysis incorporates both Gaussian, stationary, and unpolarized point sources from diverse sky locations as well as a random sky map. We have performed full-sky map reconstruction in pixel space using maximum likelihood estimation to extract the angular distribution of the SGWB. The results demonstrate that, when considering the detector noise, the TianQin+LISA+Taiji detector network can reconstruct the angular power spectrum of the stochastic background up to a maximum multipole moment of $l = 14 $, which can provide valuable information for studies on the spatial distribution of galactic compact binaries and physical imprints from the early Universe.

gr-qc↗

arXiv2025

Toward Second-Order Self-Force for Eccentric Extreme-Mass Ratio Inspirals in Schwarzschild Spacetime

An Extreme Mass Ratio Inspiral (EMRI), which corresponds to a small compact object inspirals around a massive black hole in the center of a galaxy, is one of the most important sources for future space-borne gravitational-wave (GW) detectors such as TianQin and LISA. By analyzing the emitted GW signals, we can probe the theory of gravity and the nature of black holes in the strong field region. To achieve these objectives, the second-order self-force effect should be considered in the waveform modeling. Up to now, the waveform of EMRIs including the second-order self-force effect is only achieved for the circular orbit on Schwarzschild background. In this work, we generalized the calculation of the second-order self-force to the eccentric orbits on Schwarzschild spacetime. We calculated the puncture field, and give the form of two-timescale expansion for the field equations. The corresponding numerical calculation and programming can be performed based on these results.

gr-qc↗

arXiv2025

Distinguish the environmental effects and modified theory of gravity with multiple massive black-hole binaries

In the typical data analysis and waveform modeling of the gravitational waves (GWs) signals for binary black holes (BBHs), it is assumed to be isolate sources in the vacuum within the theory of general relativity (GR). However, various kinds of matter may exist around the source or on the path to the detector, and there also exist many different kinds of modified theories of gravity. The effects of these modifications can be characterized within the parametrized post-Einstein (ppE) framework, and the corresponding phase corrections on the waveform at leading post-Newtonian (PN) order are also expressed by the additional parameters for these effects. In this work, we consider the varying-G theory and the dynamical friction of the dark matter spike as an example. Both of these two effects will modify the waveform at -4PN order, if we choose the suitable power law index for the spike. We choose to use a statistic to characterize the dispersion between the posterior of $\dot G$ for different events. For different astronomical models, we find that this statistic can distinguish these two models very effectively. This result indicates that we could use this statistic to distinguish other degenerate effects with the detection of multiple sources.

gr-qc↗

arXiv2025

Constraining the EdGB Theory with Extreme Mass-Ratio Inspirals

The Einstein-dilaton-Gauss-Bonnet (EdGB) theory is a modified theory of gravity which include a scalar field to couple with the higher order curvature terms. It has already been constrained with various observations include the gravitational wave (GW) with LIGO, Virgo and KAGRA (LVK) Collaboration. In this work, we study the capability for space-borne GW detectors to constrain the EdGB theory using the signal of Extreme Mass-Ratio Inspiral (EMRIs). We use the "numerical kludge (NK)" method to construct the waveform of EMRI in the EdGB theory, focusing on the case when the central black hole is spinless. We then study how a future space-borne gravitational wave detector, TianQin, for example, can place constraints on the EdGB theory through the detection of EMRIs. With the analysis using mismatch and Fisher Information Matrix (FIM), we find that the EdGB parameter $\sqrtα$ is expected to be constrained to the level of $\sim\mathcal{O}(0.1)$ km.

gr-qc↗

arXiv2025

Probing the Extreme-Mass-Ratio Inspirals Population Constraints with TianQin

Extreme-mass-ratio inspirals (EMRIs), consisting of a massive black hole and a stellar compact object, are one of the most important sources for space-borne gravitational wave detectors like TianQin. Their population study can be used to constrain astrophysical models that interpret the EMRI formation mechanisms. In this paper, as an initial attempt, we employ a parametrization method to describe the EMRI population model in the loss cone formation channel. This approach, however, can be extended to other models such as the accretion disc driven formation channel. We present the phenomenological characteristic of the MBH mass, spin, and redshift distributions. Then, we investigate the posterior distribution of the hyper-parameters that describe this population model. The optimistic results show that TianQin could recover almost all the posterior of the hyper-parameters within $1σ$ confidence interval. The hyper-parameters $α_1, α_2, b$, which describe the MBH mass distribution, could be measured with an accuracy of $46.4\%$, $12.6\%$, and $3\%$, respectively. The hyper-parameters $μ_z$, and $σ_z$, which describe the redshift distribution, could be measured with an accuracy of $15.4\%$ and $21.1\%$. With this estimation accuracy, the EMRI population characteristics can be effectively demonstrated, potentially serving as evidence for EMRI formation in the future studies. Furthermore, with an increasing number of detectable events, the parameter estimation for the hyper-parameters will improve and the confidence intervals will be narrowed.

astro-ph.HE↗

arXiv2025

Progress of the TianQin project

TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will consist of three Earth orbiting satellites on nearly identical orbits with orbital radii of about $10^5$ km. The satellites will form a normal triangle constellation whose plane is nearly perpendicular to the ecliptic plane. The TianQin project has been progressing smoothly following the ``0123" technology roadmap. In step ``0", the TianQin laser ranging station has been constructed and it has successfully ranged to all the five retro-reflectors on the Moon. In step ``1", the drag-free control technology has been tested and demonstrated using the TianQin-1 satellite. In step ``2", the inter-satellite laser interferometry technology will be tested using the pair of TianQin-2 satellites. The TianQin-2 mission has been officially approved and the satellites will be launched around 2026. In step ``3", i.e., the TianQin-3 mission, three identical satellites will be launched around 2035 to form the space-based gravitational wave detector, TianQin, and to start gravitational wave detection in space.

gr-qc↗

arXiv2025

Unveiling a multi-component stochastic gravitational-wave background with the TianQin + LISA network

Space-borne detectors, including TianQin and Laser Interferometry Space Antenna (LISA), are tasked with simultaneously observing the Galactic foreground, astrophysical and cosmological stochastic gravitational-wave backgrounds (SGWBs). For the first time, we employ a space-borne detector network to identify these SGWBs. Specifically, we develop a tailored likelihood for cross-correlation detection with such networks. Combined with the likelihood, we use the simulated datasets of the TianQin + LISA network to conduct an analysis for model selection and parameter estimation. In our analysis, we adopt an astrophysical background originating from extragalactic white-dwarf binaries, along with a flat cosmological background associated with the early Universe. Our results indicate that, after 4 years of operation, the network could detect a single SGWB from either astrophysical or cosmological origins, with an energy density $Ω_{\rm ast/cos}$ (10 mHz) on the order of $10^{-12}$, despite the presence of a Galactic foreground. Furthermore, to distinguish the cosmological background from both a Galactic foreground and an extragalactic background produced by white-dwarf binaries, the energy density $Ω_{\rm cos}$ should reach around $2\times 10^{-11}$.

gr-qc↗

arXiv2024

Mapping Anisotropies in the Stochastic Gravitational-Wave Background with TianQin

In the milli-Hertz frequency band, stochastic gravitational-wave background can be composed of both astronomical and cosmological sources, both can be anisotropic. Numerically depicting these anisotropies can be critical in revealing the underlying properties of their origins. For the first time, we perform a theoretical analysis of the constraining ability of TianQin on multiple moments of the stochastic background. First, we find that with a one-year operation, for a background with a signal-to-noise ratio of 16, TianQin can recover the multiple moments up to $l=4$. We also identified a unique feature of the stochastic background sky map, which is the mirror symmetry along the fixed orbital plane of TianQin. Thirdly, we explain the difference in anisotropy recovering ability between TianQin and LISA, by employing the criteria of the singularity of the covariance matrix (which is the condition number). Finally, we find that since the different data channel combinations correspond to different singularities, certain combinations might have an advantage in stochastic background map-making. We believe that the findings of this work can provide an important reference to future stochastic background analysis pipelines. It can also serve as a guideline for designing better gravitational-wave detectors aiming to decipher anisotropies in the stochastic background.

gr-qc↗

arXiv2024

Identification of Gravitational-waves from Extreme Mass Ratio Inspirals

Space-based gravitational wave detectors like TianQin or LISA could observe extreme-mass-ratio-inspirals (EMRIs) at millihertz frequencies. The accurate identification of these EMRI signals from the data plays a crucial role in enabling in-depth study of astronomy and physics. We aim at the identification stage of the data analysis, with the aim to extract key features of the signal from the data, such as the evolution of the orbital frequency, as well as to pinpoint the parameter range that can fit the data well for the subsequent parameter inference stage. In this manuscript, we demonstrated the identification of EMRI signals without any additional prior information on physical parameters. High-precision measurements of EMRI signals have been achieved, using a hierarchical search. It combines the search for physical parameters that guide the subsequent parameter inference, and a semi-coherent search with phenomenological waveforms that reaches precision levels down to $10^{-4}$ for the phenomenological waveform parameters $ω_{0}$, $\dotω_{0}$, and $\ddotω_{0}$. As a result, we obtain measurement relative errors of less than 4% for the mass of the massive black hole, while keeping the relative errors of the other parameters within as small as 0.5%.

gr-qc↗

arXiv2024

Sensitivity to anisotropic stochastic gravitational-wave background with space-borne networks

Single gravitational-wave detectors face inherent limitations in detecting the anisotropy of the stochastic background. In this work, we explore the sensitivity to anisotropic backgrounds with a network of space-borne detectors. We find that the separation between detectors plays an important role in determining the sensitivity. For the first time, we observe as large as three orders of magnitude enhancement in detection sensitivity for the multipoles with $l=5$ and 6, compared to coinciding detectors. Coordinating and optimizing the separation between two space-borne detectors can significantly enhance the network's sensitivity to the multipole components of the stochastic background. For the TianQin + LISA network, benefiting from detector separation, it is possible to achieve sensitivity levels of 2-3 orders of magnitude better than using TianQin or LISA detector alone. These findings pave the way to uncover the underlying physics of anisotropy through gravitational-wave detections.

gr-qc↗

arXiv2024

Revisiting Stochastic Gravitational-wave Background in the Strong Signal Case

Weak-signal limit is often used in estimating stochastic gravitational-wave background (SGWB) intensities. This approximation fails and the signal-to-noise ratio (SNR) can be much weaker when background signals are loud compared to the detector noise. In this work, we highlight this limitation for the SGWB detection using space-borne detector networks. For the TianQin + LISA network, the SNR estimated under the weak-signal limit might be off by as large as an order of magnitude. Contour plots of SNR over the parameter spaces are also presented to indicate regions susceptible to this discrepancy. Our results suggest that DA and DB type extragalactic double white dwarfs may yield an SGWB with SNR surpassing 100 after 1 year of operation in the weak-signal-limit scenario, with a redshift-independent merger rate of about $500\,\,{\rm Mpc^{-3}\,Myr^{-1}}$. In fact, this value falls significantly below the necessary threshold. Similar influences arise for first-order phase transitions, yet pinning down parameter regions remains formidable due to model uncertainties.

gr-qc↗

arXiv2024

Probing the Spin-Induced Quadrupole Moment of Massive Black Holes with the Inspiral of Binary Black Holes

One of the most important sources for space-borne gravitational wave detectors such as TianQin and LISA, is the merger of massivie black hole binaries. By analyzing the inspiral signals, we can probe the characteristics of massive black holes, including the spin-induced multipole moments. By verifying the relation among mass, spin, and quadrupole moment, the no-hair theorem can be tested. In this work, we analyed the capability of probing the spin-induced quadrupole moment with the inspiral signal of massive black hole binaries using space-borne gravitational wave detectors. Using the Fisher information matrix, we find that the deviation of the quadrupole moment can be constrained to the level of $10^{-1}$, and events with higher mass ratios will provide a better constraint. We also find that the late inspiral part will dominate the result of parameter estimation. The results of Bayesian analysis indicate that the capability will be significantly enhanced by considering higher modes. We also calculate the Bayes factor, and the results indicate that the model of a black hole and a Boson star can be distinguished without a doubt.

gr-qc↗

arXiv2024

Improving the Cosmological Constraints by Inferring the Formation Channel of Extreme-mass-ratio Inspirals

Extreme-mass-ratio inspirals (EMRIs) could be detected by space-borne gravitational-wave (GW) detectors, such as the Laser Interferometer Space Antenna (LISA), TianQin and Taiji. Localizing EMRIs by GW detectors can help us select candidate host galaxies, which can be used to infer the cosmic expansion history. In this paper, we demonstrate that the localization information can also be used to infer the formation channel of EMRIs, and hence allow us to extract more precisely the redshift probability distributions. By conducting mock observations of the EMRIs which can be detected by TianQin and LISA, as well as the galaxies which can be provided by the future Chinese Space Station Telescope, we find that TianQin can constrain the Hubble-Lemaître constant $H_0$ to a precision of $\sim3\%-8\%$ and the dark energy equation of state parameter $w_0$ to $\sim10\%-40\%$. The TianQin+LISA network, by increasing the localization accuracy, can improve the precisions of $H_0$ and $w_0$ to $\sim0.4\%-7\%$ and $\sim4\%-20\%$, respectively. Then, considering an illustrative case in which all EMRIs originate in AGNs, and combining the mock EMRI observation with a mock AGN catalog, we show that TianQin can recognize the EMRI-AGN correlation with $\sim 1300$ detections. The TianQin+LISA network can reduce this required number to $\sim 30$. Additionally, we propose a statistical method to directly estimate the fraction of EMRIs produced in AGNs, $f_{\rm agn}$, and show that observationally deriving this value could significantly improve the constraints on the cosmological parameters. These results demonstrate the potentials of using EMRIs as well as galaxy and AGN surveys to improve the constraints on cosmological parameters and the formation channel of EMRIs.

astro-ph.CO↗

arXiv2024

An Opacity-Free Method of Testing the Cosmic Distance Duality Relation Using Strongly Lensed Gravitational Wave Signals

The cosmic distance duality relation (CDDR), expressed as DL(z) = (1 + z)2DA(z), plays an important role in modern cosmology. In this paper, we propose a new method of testing CDDR using strongly lensed gravitational wave (SLGW) signals. Under the geometric optics approximation, we calculate the gravitational lens effects of two lens models, the point mass and singular isothermal sphere. We use functions of η1(z) = 1 + η0z and η2(z) = 1 + η0z=(1 + z) to parameterize the deviation of CDDR. By reparameterizing the SLGW waveform with CDDR and the distance-redshift relation, we include the deviation parameters η0 of CDDR as waveform parameters. We evaluate the ability of this method by calculating the parameter estimation of simulated SLGW signals from massive binary black holes. We apply the Fisher information matrix and Markov Chain Monte Carlo methods to calculate parameter estimation. We find that with only one SLGW signal, the measurement precision of η0 can reach a considerable level of 0.5-1.3% for η1(z) and 1.1-2.6% for η2(z), depending on the lens model and parameters.

astro-ph.CO↗