arXiv subjects

Yong Tang

Publications and source records attributed to Yong Tang.

At least 37 records · Page 2Linked to original sources

arXiv2025

Revisiting the fermionic quasi-bound states around Schwarzschild black holes with improved analytic spectrum

Black holes have long served as a testing ground for probing theories of gravity and quantum mechanics. Notably, fundamental fields in the neighborhood of black holes exhibit rich phenomena that could yield astrophysical observable signatures. However, exploring these structures typically requires computationally intensive numerical calculations. In this work, the dynamics of a massive Dirac field outside a Schwarzschild black hole is revisited. We propose a novel matching scheme that enables the analytical solution of the coupled first-order Dirac equation, as opposed to the conventional second-order approach. This method yields a compact and unified analytical expression for the energy spectrum, which shows improved agreement with numerical results. The improvement is due to high-order correction of angular parameter that has been ignored previously.

gr-qc↗

arXiv2025

Probing Dark Matter Spike with Gravitational Waves from Early EMRIs in the Milky Way Center

Cold dark matter may form dense structures around supermassive black holes (SMBHs), significantly influencing their local environments. These dense regions are ideal sites for the formation of extreme mass-ratio inspirals (EMRIs), in which stellar-mass compact objects gradually spiral into SMBH, emitting gravitational waves (GWs). Space-based gravitational-wave (GW) observatories such as LISA and Taiji will be sensitive to these signals, including early-stage EMRIs (E-EMRIs) that persist in the low-frequency band for extended periods. In this work, we investigate the impact of dark matter-induced dynamical friction on E-EMRIs in the Milky Way Center, model its effect on the trajectory, and calculate the resulting modifications to the GW spectrum. Our analysis suggests that this influence might be sizable and lead to detectable deviations in the spectrum, namely suppression at low frequencies and enhancement at high frequencies, therefore providing a potential probe for dark matter with future GW detectors in space, such as LISA and Taiji.

astro-ph.GA↗

arXiv2025

Effects of black hole environments on extreme mass-ratio hyperbolic encounters

Extreme mass-ratio hyperbolic encounters (EMRHEs) around the supermassive black holes will be observable at the future gravitational-wave (GW) detectors in space, such as LISA and Taiji. Here we consider such EMRHEs in the presence of surrounding matter distribution including baryonic accretion disk and dark matter (DM) spike, and estimate their effects on the orbital evolution and GW waveforms. We find that large possible impacts come from the gravitational potential of accretion disk, while the influence of DM spike is small. We also illustrate that environments can leave distinctive imprints on the GW waveforms, but resolving such modifications is found to be challenging for LISA-like detectors in the near future.

gr-qc↗

arXiv2025

Probing vector gravitational atoms with eccentric intermediate mass-ratio inspirals

Ultralight bosons, proposed as candidates for dark matter (DM), are predicted by various new physics models. In the presence of bosons with suitable masses, superradiant (SR) instability can naturally transform a spinning black hole (BH) into a gravitational atom (GA). Here we study the dynamics of intermediate mass-ratio inspirals (IMRIs) around a GA formed by ultralight vector field saturated in its SR ground state. We employ a perturbative model at the leading Newtonian order to consistently account for both the conservative effect of cloud gravity and the dissipative effect of cloud ionization. We find the cloud can make a sizable negative contribution to the secular periastron precession at binary separations comparable to the gravitational Bohr radius. Meanwhile, the backreaction of ionization could significantly accelerate the process of orbital decay and circularization. Considering reasonably small vector boson masses, we examine the adiabatic orbital evolution and gravitational waveforms of eccentric inspirals. The results indicate that vector GAs might be detectable through observations of low-frequency IMRIs by the future space-based gravitational-wave detectors, such as LISA and Taiji.

gr-qc↗

arXiv2025

Experimental Study on the Rotation-induced Reduction of Penetration Resistance in Sand

Soil-dwelling organisms have evolved diverse strategies for efficient subterranean movement. For example, the seeds of Erodium cicutarium and Pelargonium species employ continuous rotational motion for self-burial, while the angled worm lizard Agamodon angeliceps tunnels by oscillating its head around its trunk's axis. These rotational movements significantly reduce penetration resistance. This study presents comprehensive experiments investigating the effects of various factors on rotational penetration forces and energy consumption. Results reveal that force reduction follow an approximately hyperbolic decay with the tangential-to-axial velocity ratio ($u$). Penetrator geometry, particularly roundness and conical tip shape, is found to significantly influence reduction at low velocity ratios, whereas relative density and material type exhibit moderate impact. Reduction is also observed to increase with interfacial friction angle but decreases with confining pressure and depth. Energy consumption analysis shows that while penetration force-related energy decreases with $u$, total energy consumption increases due to rotational torque. For self-burrowing robot designs, lower velocity ratios are recommended to balance penetration force reduction and energy efficiency effectively.

physics.geo-ph↗

arXiv2025

Prospects for Axion Dark Matter Searches at LISA-like Interferometers

Axion or axionlike particles are one of the leading candidates for dark matter. Because of its tiny coupling with photons, axion dark matter in the background can induce distinct phase velocities for light with different parity, an effect known as birefringence. Here, we propose a modification to the polarization state of the interspacecraft laser link in LISA-like interferometers to make them sensitive to this birefringence effect. We discuss the prospects of using the Sagnac combinations to search for axion dark matter and derive the corresponding sensitivity. With this setup, we show that next-generation laser interferometers in space would have promising sensitivities on the axion-photon coupling with axion mass around $10^{-19} - 10^{-14}~\text{eV}$.

hep-ph↗

arXiv2025

IterComp: Iterative Composition-Aware Feedback Learning from Model Gallery for Text-to-Image Generation

Advanced diffusion models like RPG, Stable Diffusion 3 and FLUX have made notable strides in compositional text-to-image generation. However, these methods typically exhibit distinct strengths for compositional generation, with some excelling in handling attribute binding and others in spatial relationships. This disparity highlights the need for an approach that can leverage the complementary strengths of various models to comprehensively improve the composition capability. To this end, we introduce IterComp, a novel framework that aggregates composition-aware model preferences from multiple models and employs an iterative feedback learning approach to enhance compositional generation. Specifically, we curate a gallery of six powerful open-source diffusion models and evaluate their three key compositional metrics: attribute binding, spatial relationships, and non-spatial relationships. Based on these metrics, we develop a composition-aware model preference dataset comprising numerous image-rank pairs to train composition-aware reward models. Then, we propose an iterative feedback learning method to enhance compositionality in a closed-loop manner, enabling the progressive self-refinement of both the base diffusion model and reward models over multiple iterations. Theoretical proof demonstrates the effectiveness and extensive experiments show our significant superiority over previous SOTA methods (e.g., Omost and FLUX), particularly in multi-category object composition and complex semantic alignment. IterComp opens new research avenues in reward feedback learning for diffusion models and compositional generation. Code: https://github.com/YangLing0818/IterComp

cs.CV↗

arXiv2025

On Equation of State of Dark Matter around Massive Black Holes

The nature of Dark Matter (DM) remains mysterious despite the substantial evidence from astrophysical and cosmological observations. While the majority of DM in our universe is non-relativistic, collisionless and its equation of state (EoS) is approximately pressureless $p\simeq 0$, DM becomes relativistic near the massive black holes in galactic center. Yet its EoS is seldom discussed in the relativistic regime. Here we initially explore the possible equation of state for DM in the vicinity of Schwarzschild black holes. We work in a spherical and quasi-static background spacetime, and describe DM as a perfect fluid in equilibrium. Through numerically solving the TOV equations with physical boundary conditions, we show that DM can have static profiles near black holes and its pressure should be negative in order to support the viable density profiles $ρ$. We illustrate with two simple general equations of state, namely the power law $p \propto ρ^γ$ and the radius-dependent $p \propto r\cdot ρ$, and compare them with the observations of the Milky Way. Our findings provide insights into the model-building of DM, which should incorporate the possibility of negative pressure in the relativistic regime around black holes.

gr-qc↗

arXiv2025

AllSpark: A Multimodal Spatio-Temporal General Intelligence Model with Ten Modalities via Language as a Reference Framework

Leveraging multimodal data is an inherent requirement for comprehending geographic objects. However, due to the high heterogeneity in structure and semantics among various spatio-temporal modalities, the joint interpretation of multimodal spatio-temporal data has long been an extremely challenging problem. The primary challenge resides in striking a trade-off between the cohesion and autonomy of diverse modalities. This trade-off becomes progressively nonlinear as the number of modalities expands. Inspired by the human cognitive system and linguistic philosophy, where perceptual signals from the five senses converge into language, we introduce the Language as Reference Framework (LaRF), a fundamental principle for constructing a multimodal unified model. Building upon this, we propose AllSpark, a multimodal spatio-temporal general artificial intelligence model. Our model integrates ten different modalities into a unified framework. To achieve modal cohesion, AllSpark introduces a modal bridge and multimodal large language model (LLM) to map diverse modal features into the language feature space. To maintain modality autonomy, AllSpark uses modality-specific encoders to extract the tokens of various spatio-temporal modalities. Finally, observing a gap between the model's interpretability and downstream tasks, we designed modality-specific prompts and task heads, enhancing the model's generalization capability across specific tasks. Experiments indicate that the incorporation of language enables AllSpark to excel in few-shot classification tasks for RGB and point cloud modalities without additional training, surpassing baseline performance by up to 41.82\%. The source code is available at https://github.com/GeoX-Lab/AllSpark.

cs.AI↗

arXiv2024

RealCompo: Balancing Realism and Compositionality Improves Text-to-Image Diffusion Models

Diffusion models have achieved remarkable advancements in text-to-image generation. However, existing models still have many difficulties when faced with multiple-object compositional generation. In this paper, we propose RealCompo, a new training-free and transferred-friendly text-to-image generation framework, which aims to leverage the respective advantages of text-to-image models and spatial-aware image diffusion models (e.g., layout, keypoints and segmentation maps) to enhance both realism and compositionality of the generated images. An intuitive and novel balancer is proposed to dynamically balance the strengths of the two models in denoising process, allowing plug-and-play use of any model without extra training. Extensive experiments show that our RealCompo consistently outperforms state-of-the-art text-to-image models and spatial-aware image diffusion models in multiple-object compositional generation while keeping satisfactory realism and compositionality of the generated images. Notably, our RealCompo can be seamlessly extended with a wide range of spatial-aware image diffusion models and stylized diffusion models. Our code is available at: https://github.com/YangLing0818/RealCompo

cs.CV↗

arXiv2024

Velocity Distribution of Dark Matter Spike around Schwarzschild Black Holes and Effects on Gravitational Waves from EMRIs

Dark matter (DM) constitutes the predominant portion of matter in our universe. Despite compelling evidence, the precise characteristics of DM remain elusive. Among the leading DM candidates are weakly-interacting massive particles, which may clump into steep concentrations around the central black holes of galaxies. However, DM profiles of the resulting dense spikes remain uncertain. Here we employ the relativistic dynamics in Schwarzschild geometry and first evaluate the velocity distributions of DM within such spikes. Through variations in black hole masses and dark halo parameters, we identify universal features in DM profiles and fit them with Gaussian distributions. Additionally, we illustrate with the impact of dynamical friction on gravitational waves generated by extreme-mass-ratio inspirals (EMRIs) within DM spikes, taking into account the velocity distribution of DM in the relativistic regime. Our findings demonstrate the phase shifts in the time-domain waveform, potentially providing useful insights for probing DM in galactic centers by gravitational-wave experiments.

astro-ph.GA↗

arXiv2024

Probing Stochastic Ultralight Dark Matter with Space-based Gravitational-Wave Interferometers

Ultralight particles are theoretically well-motivated dark matter candidates. In the vicinity of the solar system, these ultralight particles can be described as a superposition of plane waves, resulting in a stochastic field with sizable amplitude fluctuations on scales determined by the velocity dispersion of dark matter. In this work, we systematically investigate the sensitivity of space-based gravitational-wave interferometers to the stochastic ultralight dark matter (ULDM) field within the frequentist framework. We derive the projected sensitivity of a single detector using the time-delay interferometry. Our results show that space-based gravitational-wave interferometers have the potential to probe unconstrained regions in parameter space and improve the current limit on coupling strengths. Furthermore, we explore the sensitivity of a detector network and investigate the optimal configuration for ULDM detection. We introduce the overlap reduction function for ULDM, which quantifies the degree of correlation between the signals observed by different detectors. We find that the configuration, where the signals observed by two detectors are uncorrelated, is the optimal choice for ULDM detection due to a smaller chance of missing signal. This contrasts with the detection of stochastic gravitational-wave background, where the correlated configuration is preferred. Our results may provide useful insights for potential joint observations involving space-based gravitational-wave detectors like LISA and Taiji, as well as other ULDM detection networks operating in the coherence limit.

hep-ph↗

arXiv2024

Dual Gravitational Wave Signatures of Instant Preheating

In the instant preheating scenario efficient particle production occurs immediately following the period of inflationary expansion in the early Universe. We demonstrate that instant preheating predicts unique gravitational wave (GW) signals arising from two distinct origins. One source is the bremsstrahlung GWs produced through the decay of superheavy particles, an inevitable consequence of instant preheating. The other is GWs generated from the nonlinear dynamics of the inflaton and coupled scalar fields. Using numerical simulations, we show that the peak of the GW spectrum shifts depending on the coupling constants of the theory. The detection of these dual GW signatures, characteristic of instant preheating, provides novel opportunities for probing the dynamics of the early Universe.

astro-ph.CO↗

arXiv2024

Detecting Ultralight Dark Matter Gravitationally with Laser Interferometers in Space

Ultralight dark matter (ULDM) is one of the leading well-motivated dark matter candidates, predicted in many theories beyond the standard model of particle physics and cosmology. There have been increasing interests in searching for ULDM in physical and astronomical experiments, mostly assuming there are additional interactions other than gravity between ULDM and normal matter. Here we demonstrate that even if ULDM has only gravitational interaction, it shall induce gravitational perturbations in solar system that may be large enough to cause detectable signals in future gravitational-wave (GW) laser interferometers in space. We investigate the sensitivities of Michelson time-delay interferometer to ULDM of various spins, and show vector ULDM with mass $m\lesssim 10^{-18}~$eV can be probed by space-based GW detectors aiming at $μ$Hz frequencies. Our findings exhibit that GW detectors may directly probe ULDM in some mass ranges that otherwise are challenging to examine.

hep-ph↗

arXiv2024

Linear dynamics and classical tests of the gravitational quantum field theory

We explore the new physics phenomena of gravidynamics governed by the inhomogeneous spin gauge symmetry based on the gravitational quantum field theory. Such a gravidynamics enables us to derive the generalized Einstein equation and an equation beyond it. To simplify the analyses, we linearize the dynamic equations of gravitational interaction by keeping terms up to the leading order in the dual gravigauge field. We then apply the linearized dynamic equations into two particular gravitational phenomena. First, we consider the linearized equations in the absence of source fields, which is shown to have five physical propagating polarizations as gravitational waves, i.e., two tensor modes, two vector modes, and one scalar, instead of two tensor polarizations in the general relativity. Second, we examine the Newtonian limit in which the gravitational fields and the matter source distribution are weak and static. By deriving the associated Poisson equation, we obtain the exact relation of the fundamental interaction coupling in the gravidynamics with the experimentally measured Newtonian constant. We also make use of nonrelativistic objects and relativistic photons to probe the Newtonian field configurations. In particular, the experiments from the gravitational deflection of light rays and the Shapiro time delay can place stringent constraints on the linearized gravidynamics in the gravitational quantum field theory.

gr-qc↗

arXiv2024

Gravitational Wave Probe of Planck-scale Physics After Inflation

Particle decays are always accompanied by the emission of graviton quanta of gravity through bremsstrahlung processes. However, the corresponding branching ratio is suppressed by the square of the ratio of particle's mass to the Planck scale. The resulting present abundance of gravitational waves (GWs), composed of gravitons, is analogously suppressed. We show that superheavy particles, as heavy as the Planck scale, can be naturally produced during the post-inflationary reheating stage in the early Universe and their decays yield dramatic amounts of GWs over broad frequency range. GW observations could hence directly probe Planck-scale physics, notoriously challenging to explore.

hep-ph↗

arXiv2024

Post-Newtonian Binary Dynamics in Effective Field Theory of Horndeski Gravity

General relativity has been very successful since its proposal more a century ago. However, various cosmological observations and theoretical consistency still motivate us to explore extended gravity theories. Horndeski gravity stands out as one attractive theory by introducing only one scalar field. Here we formulate the post-Newtonian effective field theory of Horndeski gravity and investigate the conservative dynamics of the inspiral compact binary systems. We calculate the leading effective Lagrangian for a compact binary and obtain the periastron advance per period. In particular, we apply our analytical calculation to two binary systems, PSR B 1534+12 and PSR J0737-3039, and constrain the relevant model parameters. The theoretical framework can also be extended to higher order systematically.

gr-qc↗

arXiv2024

Signatures of Ultralight Bosons in Compact Binary Inspiral and Outspiral

Ultralight bosons are well-motivated particles from various physical and cosmological theories, and can be spontaneously produced during the superradiant process, forming a dense hydrogen-like cloud around the spinning black hole. After the growth saturates, the cloud slowly depletes its mass through gravitational-wave emission. In this work we study the orbit dynamics of a binary system containing such a gravitational atom saturated in various spin-0,1,2 superradiant states, taking into account both the effects of dynamical friction and the cloud mass depletion. We estimate the significance of mass depletion, finding that although dynamical friction could dominate the inspiral phase, it typically does not affect the outspiral phase driven by the mass depletion. Focusing on the large orbit radius, we investigate the condition to observe the outspiral, and the detectability of the cloud via pulsar-timing signal in the case of black hole-pulsar binary.

gr-qc↗