arXiv subjects

Haiyuan Feng

Publications and source records attributed to Haiyuan Feng.

16 recordsLinked to original sources

arXiv2026

Images of shadow and thin accretion disk around Bardeen black hole surrounded by perfect fluid dark matter

We investigate the shadow and optical appearance of Bardeen black hole (BH) immersed in perfect fluid dark matter (PFDM). Using EHT observations of M87* and Sgr A*, we constrain the DM parameter to a narrow range $b/M \sim \mathcal{O}(10^{-1}-10^{-2})$ for M87* and to $\mathcal{O}(10^{-2}-10^{-3})$ for Sgr A*. From these constraints we derive a rough prediction for the PFDM density near the shadow scale ($R_{\mathrm{sh}}\sim5M$): $ρ_{\mathrm{PFDM}} \sim 0.27$-$2.67\,\mathrm{g/cm^3}$ for Sgr A*, dropping to $\sim10^{-24}$-$10^{-25}\,\mathrm{g/cm^3}$ at 100 pc. Moreover, increasing $b$ substantially enlarges the photon sphere, impact parameter, shadow radius, and suppresses the observed disk brightness, while the magnetic charge $g$ produces only negligible corrections completely masked by PFDM on macroscopic scales. Subsequently, we investigate the primary/secondary images, flux, and redshift profiles for the PFDM-Bardeen BH using the Novikov-Thorne disk model, and compare these quantities with those of NFW, Dehnen-type and Moore DM BHs. The four BH types exhibit distinct densities at the shadow radius and at 100 pc, offering a potential distinguishing signature. Furthermore, for all DM BH models, blueshift appears in the primary image as inclination increases, while the secondary image remains redshift dominated even at high inclinations. Hence, if significant blueshifted emission were detected at low inclination, the predictions of these four DM models would be seriously challenged.

astro-ph.HE↗

arXiv2026

Shadow of rotating black hole surrounded by dark matter

Dark matter (DM), a fundamental cosmic component, motivates the study of its influence on black hole (BH) shadows, especially for spinning BHs confirmed by EHT observations. This work generalizes the Schwarzschild BH surrounded by DM to an axisymmetric Kerr BH using the Newman-Janis Algorithm (NJA), investigating the resulting event horizon and ergosphere structures. Employing null geodesics, we examine the effects of DM mass ($Δ$M) on BH shadow, including its radius, distortion, and the associated energy emission rate. Our analysis reveals that DM has a negligible effect below a critical mass, once this threshold is surpassed, all BH structures expand significantly. Furthermore, DM robustly contributes to the shadow maintaining a near circular shape, even for highly spinning BHs. This pronounced structural expansion under high DM mass may potentially exceed current observational constraints, suggesting that DM must either be absent in the immediate vicinity of the BH or its localized mass must remain below this critical value to be consistent with astrophysical observations.

gr-qc↗

arXiv2026

The perturbation solutions to the Blandford-Znajek mechanism in the Kerr-Sen black hole

We investigate the steady, axisymmetric, force-free magnetosphere of Kerr-Sen black hole (BH) within the framework of the Einstein-Maxwell-dilaton-axion (EMDA) theory. By perturbatively solving the nonlinear Grad-Shafranov (GS) equation, we determine the magnetic field configuration and quantify the influence of the dilaton parameter $r_2$ on the energy extraction rate and radiative efficiency. Our results show that both the energy extraction power and the radiative efficiency increase with $r_2$, exceeding those of the standard Kerr BH, whereas the extraction efficiency remain consistent with the Kerr case. In addition, we perform $χ^2$ statistical analysis using observational data from six binary BH systems, which indicates that the Kerr BH currently provides a better fit for bulk Lorentz factors $Γ= 2$ and $5$.

gr-qc↗

arXiv2026

Newtonian potential from scattering amplitudes in super-renormalizable gravity

Based on the classical limit of relativistic scattering amplitudes, we compute the coupling between a general super-renormalizable gravity and massive scalar particles. This allows us to derive the $D$-dimensional metric corrections at both tree-level and one-loop level-the latter containing the first calculation by using newly derived three-graviton Feynman rules. By introducing Newtonian potential function $Φ\equiv\frac{h_{00}}{2}$, we reproduce at tree level, $\mathcal{O}(G)$, the well-known result proportional to the error function in four-dimensional spacetime. Furthermore, we obtain the loop-level contributions to the potential function at order $\mathcal{O}(G^2)$ and perform a numerical analysis of its behavior at large distances. Our results indicate that, at the one-loop level, the magnitude of the potential increases gradually with distance in the asymptotic regime.

hep-th↗

arXiv2026

The stability of the de-Sitter universe in nonlocal gravity

We constructed the ghost-free condition for nonlocal gravity using de-Sitter background field expansion and identified the structure of the nontrivial form factors. Our analysis shows that the particle spectrum of this model is nearly equivalent to general relativity(GR), with the potential addition of a scalar particle with positive mass m. Additionally, by employing recursion relations, we established the equivalence between nonlocal gravity and higher-derivative gravity. Moreover, we provided a comprehensive proof of the stability of de-Sitter solution within the nonlocal framework.

gr-qc↗

arXiv2025

Shadow and thin accretion disk around Ayón-Beato-García black hole coupled with cloud of strings

In this paper, we investigate the shadow and thin accretion disk around Ayón-Beato-García (ABG) black hole (BH) coupled with a cloud of strings (CS), characterized by the nonlinear electrodynamics (NLED) parameter $g$, and the CS parameter $a$. By comparing shadow diameters with Event Horizon Telescope (EHT) observations of M87$^{*}$ and Sgr A$^*$, we have established constraints on the BH parameters $g$ and $a$. Additionally, we analyze the BH shadow, lensing ring, and photon ring features for the ABG BH coupled with CS. Our results indicate that the shadow radius increases monotonically with the CS parameter $a$, while it decreases with increasing $g$. Finally, the study explores the physical properties and observational signatures of thin accretion disks around ABG BH with CS. The results show that an increase in parameter $g$ leads to a hotter and more luminous disk, while an increase in parameter $a$ results in a cooler and less luminous disk.

gr-qc↗

arXiv2025

Rotating Charged Black Holes with Scalar Hair Constructed via the Newman-Janis Algorithm: Accretion Disk Structure and Shadow Characteristics

In this paper, we generate a rotating charged black hole (BH) with scalar hair via the Newman--Janis algorithm (NJA) and study its thin accretion disk and shadow. The structure of the event horizon and ergosurface is analyzed in detail, revealing how the charge parameter $Q$ and scalar hair parameter $s$ influence the spacetime geometry. We analyze the energy flux and temperature distribution of the accretion disk, finding that increasing either $Q$ or $s$ leads to higher energy flux and peak temperature. The BH shadow is also examined, showing that its apparent size decreases monotonically with increasing $Q$ or $s$. Notably, in the near-extremal regime, the shadow develops a distinctive cuspy edge, indicative of strong light bending in the scalarized and charged spacetime. By comparing the theoretically predicted shadow diameter with Event Horizon Telescope (EHT) observations of Sgr A$^*$, we derive observational constraints on the model parameters. For inclination angles of $17^\circ$ and $90^\circ$, a joint analysis constrains the charge parameter to $0<Q<0.522745$ (at fixed $s=0.1$) and the scalar hair parameter to $0<s<0.283373$ (at fixed $Q=0.3$). Our results demonstrate how scalar hair and electric charge leave imprints on accretion disk emissions and black hole shadows, offering new observational signatures for testing gravity theories beyond general relativity.

gr-qc↗

arXiv2025

Thin accretion disk around Schwarzschild-like black hole in bumblebee gravity

The physical properties and optical appearance of a thin accretion disk surrounding a Schwarzschild-like black hole (BH) are investigated within the framework of bumblebee gravity. To understand how the Lorentz symmetry breaking (LSB) parameter $l$ affects the disk's behavior, we analyze main characteristics such as energy flux, temperature distribution, and emission spectrum. In addition, direct and secondary images of the accretion disk are generated and examined to explore how both the observational inclination angle and the LSB parameter $l$ shape the visual profile. Furthermore, we compute the redshift and observed flux distributions of the disk from the perspective of distant observers at various inclination angles. Our results indicate that the redshift factor grows as $l$ decreases. When the parameter $l$ assumes negative values, the BH exhibits enhanced luminosity with decreasing $l$. These findings highlight the crucial influence of the LSB parameter $l$ on the observable features of BHs.

gr-qc↗

arXiv2025

Probing Einstein-Maxwell-Scalar Black hole via Thin Accretion Disks and Shadows with EHT Observations of M87* and Sgr A*

We investigated the shadows and thin accretion disks of Einstein-Maxwell-Scalar (EMS) black hole. Firstly, we investigated the influence of EMS parameters on the black hole shadow using the null geodesic method and constrained these parameters based on EHT observations of M87* and Sgr A*. Furthermore, we analyzed the direct emission, lensing ring, and photon ring structures in EMS black hole. Comparing our results with the Schwarzschild and Reissner-Nordstr$\ddot{\mathrm{o}}$m (RN) black holes, we found that the Schwarzschild black hole exhibits the largest shadow radius and the highest observed intensity.

gr-qc↗

arXiv2025

Damping of gravitational waves in f(R) gravity

We investigate the damping of gravitational waves (GW) in $f(R)$ gravity by matter. By applying the kinetic theory, we examine the first-order approximation of the relativistic Boltzmann equation. In the flat spacetime, we derive the evolution equations for waves in $f(R)$ gravity and demonstrate that Landau damping is absent while collision damping is present. In the Friedmann-Robertson-Walker (FRW) cosmology, we also examine the dynamical equations for the two modes. Furthermore, in the model $f(R) = R + αR^2$, we investigate the effect of the mass term on wave amplitude decay within the neutrino system. We observe that the tensor mode with $m = 1 \, \text{eV}$ exhibits faster decay compared to other cases, while the scalar mode with $m = 1 \, \text{eV}$ appears to suppress decay.

gr-qc↗

arXiv2024

Thin accretion disk and shadow of Kerr-Sen black hole in Einstein-Maxwell-dilaton-axion gravity

We investigate the thin disk and shadow of Kerr-Sen black hole in Einstein-Maxwell-dilaton-axion gravity. The results reveal that as the dilaton parameter $r_2$ increase, the energy flux, the radiation temperature, the spectra luminosity, and the radiative efficiency of the disk all increase. By narrowing down the dilaton parameter range to $0\leqslant \frac{r_2}{M}\leqslant0.4$, we discover that in the high-frequency region, the Kerr-Sen black hole demonstrates higher energy output compared to the Kerr black hole. We also investigated the shadow of Kerr-Sen black hole in a uniform plasma environment. For fixed inclination angle, dilaton, and spin parameters, the shadow increases as the homogeneous plasma parameter $k$ increases. Conversely, when $k $ and $a$ are fixed, an increase in $r_2$ leads to a decrease in the shadow. Finally, we constrain the model parameters with observational data from M87* and Sgr A*.

gr-qc↗

arXiv2024

Thin accretion disk around black hole in Einstein-Maxwell-scalar theory

We examine the accretion process in a thin disk surrounding a supermassive black hole within the framework of Einstein-Maxwell-scalar (EMS) gravity. Our investigation aims to elucidate how variations in model parameters affect different physical properties of the disk. When keeping EMS parameters $β$ and $q$ constant, we observe a reduction in radiation flux and temperature as $α$ increases. However, the luminosity and radiative efficiency exhibit relatively minor variation. Conversely, under fixed $α$ and $q$, an escalation in $β$ leads to heightened levels of radiation flux, temperature, luminosity, and radiative efficiency. These results underscore the diverse influences of model parameters on observable metrics, providing valuable insights for the astronomical study of distinct black holes.

gr-qc↗

arXiv2024

Stability of the de-Sitter universe: One-loop nonlocal $f(R)$ gravity

With the method of the background field expansion, we investigate the one-loop quantization of the Euclidean nonlocal $f(R)$ model in the de-Sitter universe. We obtain the ghost-free condition (GFC) based on the transformation from the Jordan frame to the Einstein frame and the classical stability condition (CSC) satisfied $f^{(0)}_{RR}-ϕ_0F^{(0)}_{RR}<0$. We present the on-shell and off-shell one-loop effective action and quantum stability condition (QSC) by utilizing the generalized zeta-function. We find that under the fulfillment of GFC, CSC and QSC are inconsistent.

gr-qc↗

arXiv2024

Choked accretion onto Kerr-Sen black holes in Einstein-Maxwell-dilaton-axion gravity

We investigate the process of an ultrarelativistic fluid accreted onto axisymmetric Kerr-Sen black holes in Einstein-Maxwell-dilaton-axion theory. We obtain the solution describing the velocity potential of a stationary irrotational fluid with a stiff equation of state and the solution for the streamlined diagram of the quadrupolar flow. We also investigate how the solution's coefficients and the stagnation points are affected by the parameters. The injection rate, the ejection rate, and the critical angle are discussed in detail. We find that with an increasing dilaton parameter the ratio of the ejection rate to the injection rate increases and that the radiative efficiency is larger, while the redshift is lower, compared to the Kerr black hole.

astro-ph.HE↗

arXiv2022

Adiabatic accretion onto black holes in Einstein-Maxwell-scalar theory

We study the adiabatic accretion process of ordinary baryonic gas onto spherically symmetric black holes in Einstein-Maxwell-scalar theory, with two parameters $α$ and $β$ in the coupling term. Especially, we demonstrate the range of the transonic points in terms of the charge-to-mass ratio squared and the dimensionless coordinate radius, in two important classes of black holes as examples. Further, we find that the two coupling parameters give modifications to the mass accretion rate at different orders of the sound speed at infinity. We also present their different effects on the temperature ratios of the accreted gas.

gr-qc↗

arXiv2020

Horizon thermodynamics in $f(R,R^{μν}R_{μν})$ theory

We investigate whether the new horizon first law still holds in $f(R,R^{μν}R_{μν})$ theory. For this complicated theory, we first determine the entropy of black hole via Wald method, then we derive the energy by using the new horizon first law, the degenerate Legendre transformation, and the gravitational field equations. For application, we consider the quadratic-curvature gravity and firstly calculate the entropy and the energy for a static spherically symmetric black hole, which reduces to the results obtained in literatures for a Schwarzschild-(A)dS black hole.

gr-qc↗