arXiv subjects

Qianchuan Wang

Publications and source records attributed to Qianchuan Wang.

6 recordsLinked to original sources

arXiv2025

On-axis absorption and scattering of charged massive scalar waves by Kerr-Newman black-bounce spacetime

We investigate the absorption and scattering of charged massive scalar waves by the Kerr-Newman black-bounce spacetime when the waves are incident along the rotation axis. Our findings indicate that a faster (slower) rotating spacetime or a more repulsive (attractive) electric force tends to reduce (increase) the absorption cross section and results in larger (smaller) angular widths of the scattered wave oscillations. We find that the rotation parameter exerts a suppressive influence on superradiance, which contrasts with the enhancing effect of the repulsive electric force. It is worth mentioning that the regularization parameter $k$ is found to modify the absorption or scattering cross sections only weakly, but can cause a noticeable reduction of superradiance. To further clarify the role of the parameters in superradiance, we study the energy extraction efficiency in the electric Penrose process. For particles moving along the rotation axis, we find that the influence of the parameters ($a, q, k$) on this efficiency is consistent with their effects on superradiance. We also discuss potential astrophysical applications, showing that particles in this process could be accelerated to ultrahigh energies in realistic environments, and could therefore be used to constrain black hole parameters. For the effect of field mass, it is found that a heavier scalar field leads to a larger absorption cross section and a wider interference fringe of the differential scattering cross section. When superradiance happens, i.e., the absorption cross section becomes negative, it is also found that the differential scattering cross section only changes smoothly, with no apparent qualitative feature showing up.

gr-qc↗

arXiv2025

Scattering of charged massive scalar waves by Kerr-Newman black holes

The scattering of charged massive scalar waves by Kerr-Newman black holes, with incidence along the equatorial plane, is investigated in this work. The differential scattering cross section is computed using the partial wave method, with the forward divergence handled via the series reduction technique. For the first time, we systematically examine the influence of the black hole charge, electromagnetic interactions, and field mass on the equatorial cross section. Our results reveal that regardless of whether the electromagnetic interaction is present or not, the frame-dragging effect shifts the glory away from the exact backward direction and can place interference minima there, contrasting with the on-axis scattering case. The average scattered flux intensity at the medium to large scattering angles exhibits a large enhancement as the Lorentz attraction or field mass increases, particularly in the slowly rotating regime, with the enhancement being frequency-dependent. When superradiance occurs, we observe that the cross section in the prograde scattering angles ($\sim 135^{\circ} < ϕ< 270^{\circ}$) increases as the black hole spin increases, due to enhanced prograde partial wave contributions. Meanwhile, the superradiant scattering cross section increases in all (except the forward) directions when the Lorentz force becomes more repulsive. These findings highlight unique equatorial-plane signatures of charged, rotating spacetimes, distinguishing them from prior on-axis analyses.

gr-qc↗

arXiv2025

Weak deflection angle of charged signal in magnetic fields

We use the perturbative method to study the influence of the magnetic field on the weak deflection angle of charged signals in magnetized stationary and axisymmetric spacetimes within general electromagnetic potentials. The deflection angle is expressed as a series expansion of the inverse of the impact parameter $b$, with coefficients determined by the asymptotic expansions of the metric functions and the electromagnetic four-potential. It is found that in general, the deflection angle can always be separated into two parts, the usual gravitational part as for neutral particles, and the electromagnetic part due to the interaction between the (electro)magnetic field and the signal. The leading order of the gravitational, electrostatic (from nonzero spacetime charge) and magnetic (from nonzero magnetic dipole moment) contributions are $b^{-1},\,b^{-1}$ and $b^{-2}$ respectively. The entire electromagnetic part is enhanced by the large specific charge of elementary particles but suppressed by the reciprocal Lorentz factor. The deflection angle result is then applied to three spacetimes with intrinsic or externally enforced magnetic fields. Effects of the magnetic field on the deflection angle from various parameters, including the spacetime spin, magnetic dipole moment and magnetic parameters, are analyzed. In all these cases, it is found that in the weak deflection limit, these effects agree with the expectation for a Lorentz force; that is, an attractive (or repulsive) one will enlarge (or decrease) the deflection angle.

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arXiv2024

Absorption and scattering of charged scalar waves by charged Horndeski black hole

We investigate the absorption and scattering of a charged massive scalar field by a charged Horndeski black hole using both the approximation or classical geometric method and the partial wave method and compare the numerical and analytical results, which are found to agree with each other very well. We observe that an increase in either the BH charge $Q$ or the field charge $q$ when $qQ>0$ leads to a smaller absorption cross section and a widening of the interference fringes in the scattering cross section, while the increase in the field mass enlarges the absorption cross section and the width of the interference fringes. Compared to the Reissner-Nordstr$\ddot{\rm{o}}$m BH with the same charge and other parameter settings, the absorption and scattering cross sections of the charged Horndeski BH are higher, and its interference fringes are narrower. We also investigate the effect of the field charge $q$ on the absorption and scattering cross sections when superradiance is triggered. It is shown that the total absorption cross section can be negative, and the scattering intensity can be significantly enhanced by superradiance.

gr-qc↗

arXiv2023

Periapsis shift in spherically symmetric spacetimes and effect of electric interaction

The periapsis shift of charged test particles in arbitrary static and spherically symmetric charged spacetimes are studied. Two perturbative methods, the near-circular approximation and post-Newtonian methods, are developed, and shown to be very accurate when the results are found to high orders. The former method is more precise when the eccentricity $e$ of the orbit is small while the latter works better when the orbit semilatus rectum $p$ is large. Results from these two methods are shown to agree with each other when both $e$ is small and $p$ is large. These results are then applied to the Reissner-Nordström spacetime, the Einstein-Maxwell-dilation gravity and a charged wormhole spacetime. The effects of various parameters on the periapsis shift, especially that of the electrostatic interaction, are carefully studied. The periapsis shift data of the solar-Mercury is then used to constrain the charges of the Sun and Mercury, and the data of the Sgr A$^*$-S2 periapsis shift is used to find, for the first time using this method, constraints about the charges of Sgr A$^*$ and S2.

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arXiv2023

Deflection in higher dimensional spacetime and asymptotically non-flat spacetimes

Using a perturbative technique, in this work we study the deflection of null and timelike signals in the extended Einstein-Maxwell spacetime, the Born-Infeld gravity and the charged Ellis-Bronnikov (CEB) spacetime in the weak field limit. The deflection angles are found to take a (quasi-)series form of the impact parameter, and automatically takes into account the finite distance effect of the source and observer. The method is also applied to find the deflections in CEB spacetime with arbitrary dimension. It's shown that to the leading non-trivial order, the deflection in some $n$-dimensional spacetimes is of the order $\mathcal{O}(M/b)^{n-3}$. We then extended the method to spacetimes that are asymptotically non-flat and studied the deflection in a nonlinear electrodynamical scalar theory. The deflection angle in such asymptotically non-flat spacetimes at the trivial order is found to be not $π$ anymore. In all these cases, the perturbative deflection angles are shown to agree with numerical results extremely well. The effects of some nontrivial spacetime parameters as well as the signal velocity on the deflection angles are analyzed.

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