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Xin-Dong Du

Publications and source records attributed to Xin-Dong Du.

6 recordsLinked to original sources

Extreme mass-ratio inspirals around rotating accelerating black holes

Extreme mass-ratio inspirals (EMRIs) can magnify small departures from Kerr dynamics into appreciable gravitational-wave phase shifts accumulated over many orbital cycles. We exploit this sensitivity to investigate the imprint of a rotating black hole's acceleration on an EMRI waveform. The spinning C metric poses two obstacles to the standard Kerr flux framework: the spacetime is not asymptotically flat, and the acceleration breaks the reflection symmetry that supports exactly equatorial circular timelike orbits. For sufficiently small acceleration $AM$, we therefore formulate the calculation in an intermediate Kerr-like wave zone satisfying $M/r\ll1$ and $Ar\ll1$, and construct a near-equatorial circular orbit by examining its coupled radial--polar stability. We derive the separated point-particle source for the spin$-2$ radial Teukolsky equation, construct a regular normalized angular solution, solve the radial equation using the Sasaki--Nakamura transformation and the Green function method, and couple the resulting horizon and far-zone fluxes to the adiabatic evolution of stable near-equatorial circular orbits. The framework recovers the Kerr limit and reproduces the dominant $l=2$ Kerr fluxes with relative errors of order $10^{-7}$. Acceleration modifies both radiation reaction and the orbital frequency, producing a characteristic nonmonotonic accumulated dephasing. For $M=10^6M_\odot$, $m_s/M=10^{-5}$, $a/M=0.7$, and $AM=3\times10^{-7}$, the dominant-mode dephasing slightly exceeds $1$ rad over one year. Thus even weak acceleration can generate an order-radian secular phase imprint on long-duration EMRIs within the controlled regime of the present approximation.

gr-qc

Probing near-zone magnetic fields with extreme mass-ratio inspirals

We investigate whether weak near-zone magnetic fields can leave observable imprints on extreme-mass-ratio inspiral (EMRI) waveforms. The central massive black hole is modeled by the magnetized Schwarzschild, or Ernst, solution, and the secondary compact object is treated as a neutral point particle on equatorial circular geodesics. We compute the magnetic corrections to the circular-orbit quantities and the innermost stable circular orbit, and then evolve the inspiral using a hybrid, source-corrected Regge--Wheeler--Zerilli approximation, in which the Schwarzschild wave-propagation potentials are kept fixed while the source is evaluated on the magnetized orbit. For a fiducial system with \(M=10^6M_\odot\) and \(μ=10M_\odot\), a field strength \(B\simeq 4\times10^{-5}M^{-1}\), corresponding to \(B_{\rm phys}\sim10^9\,{\rm G}\), produces a one-year dephasing of about \(1.3\) rad and reaches the adopted LISA-noise-weighted mismatch threshold. Our results suggest that EMRIs can in principle probe extremely strong near-zone magnetic fields, whereas ordinary magnetic environments around massive black holes are likely too weak to produce detectable effects within the present approximation.

gr-qc

Stable massless scalar polarization of f(R) gravity

Polarization is a prominent feature of gravitational wave observations and can be used to distinguish between different modified gravity theories. Compared to General Relativity, f(R) gravity exhibits an additional polarization originating from a scalar field, which is a combination of the longitudinal and breathing modes. When the scalar mass of f(R) is zero, the mixed mode will reduce to a pure breathing mode with the disappearance of the longitudinal mode. However, this reducing seems to be disallowed because a positive scalar mass is often required to maintain the stability of the cosmological perturbation. In fact, the massless scalar case can provide a stable perturbation, but more detailed constraints need to be considered. For the completeness of the polarization analysis, we explore the possibility that there are stable massless scalar polarizations in viable dark energy f(R) models. We find that the existence of stable massless scalar polarization depends on the structure of f(R) model and can be used to distinguish different models in f(R) gravity.

gr-qc

New generalized uncertainty principle with parameter adaptability for the minimum length

There have been many papers suggesting that the parameter of the generalized uncertainty principle should be negative rather than positive in some specific scenarios, and the negative parameter can remove the minimum length. However, the minimum length is a model-independent feature of quantum gravity and it should not be affected by the specific scenarios. In order to solve this contradiction, we derive a new generalized uncertainty principle to reflect a fixed and unified minimum length in both cases of positive and negative parameters.

gr-qc

Removing the divergence of Chandrasekhar limit caused by generalized uncertainty principle

The usual generalized uncertainty principle will lead to a divergent mass limit of white dwarf, and this divergence should be prevented for both scenarios including positive and negative parameters of generalized uncertainty principle. Although it has been shown that negative parameter can directly restore the mass limit, the underlying reason is not given to explain why the negative sign appears under the condition of white dwarf. In order to solve this problem, we derive a field-dependent parameter expression whose sign can change depending on the species of spin fields. Besides, we find that the actual physical effect of the negative sign is aimed at limiting the exorbitant uncertainty of momentum.

astro-ph.HE

The Influence of Approximation in Generalized Uncertainty Principle on Black Hole Evaporation

The generalized uncertainty principle is often used to modify various thermodynamics systems by regarding the greater-than-equal relation as an approximate relation. We give a method to improve this approximation and compare the differences between the original and improved methods during the evaporation of black hole from two aspects of positive and negative parameters. Finally, we prove the rationality of the improved method and give some guiding opinions.

gr-qc