arXiv subjects

Towe Wang

Publications and source records attributed to Towe Wang.

17 recordsLinked to original sources

arXiv2025

Dark matter distributions around Schwarzschild-like black holes in bumblebee and Kalb-Ramond models

A central black hole can attract a dark matter cluster and generate a spike in the density profile, as demonstrated by detailed analysis of Schwarzschild and Kerr black holes in the past. Do different black holes attract dark matter differently? To get a fair answer to this question, we customize a relativistic framework to grow general static spherical black holes in dark matter halos and investigate how deviations from the Schwarzschild geometry modify the dark matter spike for the first time. The framework is applied to a class of Schwarzschild-like black hole solutions in Lorentz-violated gravity models -- one in the bumblebee model and two in the Kalb-Ramond model. For these black holes, the answer is no if initially the dark matter has a constant distribution, but the answer is yes if it has a Hernquist profile initially.

gr-qc↗

arXiv2024

Accretion disks around magnetically charged black holes in string theory with an Euler-Heisenberg correction

A relativistic model of geometrically thin and optically thick accretion disks is worked out for a class of magnetically charged black holes, which are solutions to the Einstein-Maxwell-dilaton theory with a dilaton-coupled Euler-Heisenberg correction. Constraints on black hole parameters are derived from the subextremality condition and energy conditions. The Keplerian orbits, the time-averaged energy flux, the local temperature, the specific luminosity and the conversion efficiency of accreting mass into radiation are obtained and compared with Schwarzschild and Gibbons-Maeda-Garfinkle-Horowitz-Strominger black holes.

gr-qc↗

arXiv2024

Image of Kerr-de Sitter black holes illuminated by equatorial thin accretion disks

To explore the influence of the cosmological constant on black hole images, we have developed a comprehensive analytical method for simulating images of Kerr-de Sitter black holes illuminated by equatorial thin accretion disks. Through the application of explicit equations, we simulate images of Kerr-de Sitter black holes illuminated by both prograde and retrograde accretion disks, examining the impact of the cosmological constant on their characteristic curves, relative sizes, and observed intensities. Our findings reveal that, in comparison to Kerr black holes, the cosmological constant not only diminishes the relative size of a black hole but also amplifies its luminosity. Moreover, an observer's relative position in the universe ($r_0/r_C$) can influence both the relative size and luminosity of a black hole, where $r_0$ is the distance from the observer to the black hole, $r_C$ is the cosmological horizon determined by the value of the cosmological constant $Λ$.

gr-qc↗

arXiv2024

Compton scattering in Bandos-Lechner-Sorokin-Townsend nonlinear electrodynamics

The nonlinear electrodynamics proposed by Bandos, Lechner, Sorokin and Townsend is a remarkable theory that unifies Maxwell, Bialynicki-Birula and ModMax theories, which are known theories invariant under conformal transformations and electromagnetic duality transformations. In the Bandos-Lechner-Sorokin-Townsend nonlinear electrodynamics, we calculate the energy flux density, dispersion relations, refractive indices, phase and group velocities of plane waves as well as the changes of the photon wavelength in the Compton scattering process in the presence of a constant uniform electromagnetic background. Our results are useful for testing and constraining this new theory of nonlinear electrodynamics.

hep-ph↗

arXiv2023

Reduced Kiselev black hole

The Kiselev model describes a black hole surrounded by a fluid with equations of state $p_r/ρ=-1$ and $p_t/ρ=(3w+1)/2$ respectively in radial and tangential directions. It has been extensively studied in the parameter region $-1 0$, then a new horizon of black hole type will emerge. This case has been mentioned in Kiselev's pioneer work but seldom investigated in the literature. Referring to it as reduced Kiselev black hole, we revisit this case with attention to its causal structure, thermodynamics, shadow cast and weak-field limit. An alternative interpretation and extensions of the black hole are also discussed.

gr-qc↗

arXiv2023

Transverse electric waves in Bandos-Lechner-Sorokin-Townsend nonlinear electrodynamics

In the generalized Born-Infeld electrodynamics discovered by Bandos, Lechner, Sorokin and Townsend, we study transverse electric waves propagating perpendicular to a constant magnetic field background in a parallel-plate waveguide. The directions of propagation and polarization of the waves are perpendicular to each other, and both of them are parallel to the perfectly conducting plates. Two specific configurations are studied, in which the background magnetic field is either normal to the plates or along the polarization direction. The dispersion relation, the velocity and the cutoff frequency of the lowest-order lowest-frequency mode are calculated in both configurations. This paves the way for a potential test of the generalized Born-Infeld electrodynamics.

physics.class-ph↗

arXiv2023

Images of nonsingular nonrotating black holes in conformal gravity

The accretion disk around a black hole and its emissions play an essential role in theoretical analysis of the black hole image. In the literature, two analytical toy models of accretions are widely adopted: the spherical model and the thin disk model. They are different geometrically but both thin optically. We polish them for free-falling accretions around static spherical black holes. As an application, we investigate the images of a class of nonsingular black holes conformally related to the Schwarzschild black hole. These black holes are vacuum solutions of a family of conformal gravity theories. Results are compared with the Schwarzschild black hole of the same mass. Our results indicate that the conformal factor does not affect the shadow radius seen by distant observers, but it leaves an imprint on the intensity image of black hole.

gr-qc↗

arXiv2021

Shadow of the wormholelike static aether solution

Recently, an analytical solution in Einstein-aether theory was presented explicitly in isotropic coordinates. It is characterized by a mass parameter $m$ and a combined coupling constant $c_{14}$. By a coordinate transformation, we verify this solution is equivalent to the previously known static aether solution. Assuming photons couple minimally to aether and gravity, we investigate the photon sphere and shadow of the solution by varying $c_{14}$. Results are compared with those of the Schwarzschild black hole.

gr-qc↗

arXiv2021

Gravitational effect of plasma particles on the shadow of Schwarzschild black holes

Considering a Schwarzschild black hole surrounded by a fully ionized hydrogen plasma, we study the effect of the gravitational field of the plasma particles on the shadow. We take a formalism in which this effect is unified with the refractive effect of the plasma medium studied previously, but the two effects are characterized by two independent parameters. For semi-realistic values of parameters, we find their corrections to the shadow radius are both negligible, and the gravitational correction can overtake the refractive correction for active galactic nuclei of masses larger than $10^9M_{\odot}$. With unrealistically large values of parameters, we illustrate the two effects on the light trajectories and the intensity map.

gr-qc↗

arXiv2021

Notes on diffusive and shear quasinormal modes of black branes

In the literature, to extract the dispersion relation of low-frequency quasinormal modes in both diffusive and shear channels, it is a customary recipe to assume firstly $ω\sim\mathcal{O}$ to solve the equation of motion and finally $ω\sim\mathcal{O}(q^2)$ when applying the Dirichlet boundary condition. The two assumptions appear confusing though the recipe usually gives the same result as that from other channels or from the Kubo formula. We refine the recipe by assuming $ω\sim\mathcal{O}(q^2)$ from the beginning to the end, and demonstrate it in the diffusive channel of the Schwarzschild black brane and the shear channel of the Gauss-Bonnet black brane.

hep-th↗

arXiv2019

Shear quasinormal modes of Gauss-Bonnet black brane: the first post-hydrodynamic order

Assuming $ω=\sum_n C^{(n)}q^{2n}$ in the low-frequency limit, we apply the refined recipe to compute the dispersion relation of shear quasinormal modes of the Gauss-Bonnet black brane. Treating the Gauss-Bonnet parameter $\lagb$ nonperturbatively and the momentum $q$ perturbatively, we work out $C^{(1)}$, $C^{(2)}$, confirm previous results in the literature and pave the way to a general formula for $C^{(n)}$.

hep-th↗

arXiv2018

Action growth rates of black holes in the Chern-Simons modified gravity

Among many modified gravity theories, the Chern-Simons modified gravity stands out as one of the few examples whose Dirichlet boundary problem has been well studied. Known solutions to this theory include the Schwarzschild black hole and a slowly rotating black hole. Making use of the Dirichlet boundary term of this theory, we calculate the late-time action growth rates of the Wheeler-DeWitt patch for the Schwarzschild and the slowly rotating solutions. In light of the conjecture of complexity/action duality, the result has implications on the quantum complexity of a state in the dual field theory.

hep-th↗

arXiv2018

Maximal volume behind horizons without curvature singularity

The black hole information paradox is related to the area of event horizon, and potentially to the volume and singularity behind it. One example is the complexity/volume duality conjectured by Stanford and Susskind. Accepting the proposal of Christodoulou and Rovelli, we calculate the maximal volume inside regular black holes, which are free of curvature singularity, in asymptotically flat and anti-de Sitter spacetimes respectively. The complexity/volume duality is then applied to anti-de Sitter regular black holes. We also present an analytical expression for the maximal volume outside the de Sitter horizon.

gr-qc↗

arXiv2017

Non-canonical two-field inflation to order $ξ^2$

In non-canonical two-field inflation models, deviations from the canonical model can be captured by a parameter $ξ$. We show this parameter is usually one half of the slow-roll order and analytically calculate the primordial power spectra accurate to order $ξ^2$. The super-horizon perturbations are studied with an improved method, which gives a correction of order $ξ^2$. Three typical examples demonstrate that our analytical formulae of power spectra fit well with numerical simulation.

gr-qc↗

arXiv2017

Membrane paradigm of the static black bottle

In the membrane paradigm of black holes, it is usually assumed that the normal vector of the stretched horizon has a vanishing acceleration. This assumption breaks down for black bottles, a class of solutions discovered recently in the asymptotically anti-de Sitter spacetime. In this paper, the membrane paradigm is generalized to the stretched horizon with a nonvanishing acceleration of normal vector, and then it is applied to the static black bottle. In this example, the membrane stress tensor and the fluid quantities are similar to those of black holes, while the fluid continuity equation and the Navier-Stokes equation are well satisfied in the near-horizon limit.

gr-qc↗

arXiv2016

Membrane paradigm of black holes in Chern-Simons modified gravity

The membrane paradigm of black hole is studied in the Chern-Simons modified gravity. Derived with the action principle a la Parikh-Wilczek, the stress tensor of membrane manifests a rich structure arising from the Chern-Simons term. The membrane stress tensor, if related to the bulk stress tensor in a special form, obeys the low-dimensional fluid continuity equation and the Navier-Stokes equation. This paradigm is applied to spherically symmetric static geometries, and in particular, the Schwarzschild black hole, which is a solution of a large class of dynamical Chern-Simons gravity.

gr-qc↗

arXiv2013

A quantum oscillator model for entropic gravity

In Verlinde's theory of entropic gravity, the internal degrees of freedom are marked by "bits", but the microscopic origin of "bits" is unknown hitherto. To this direction, we adopt the quantum harmonic oscillators to naively model the internal degrees of freedom. In this model, the equipartition relation is modified at the low temperature. The Newton's law and Poisson's equation of gravity are reproduced at small distances, but they receive appreciable corrections at large distances. Geometrization of gravity for this model is explored, resulting in modifications to Einstein equations.

hep-th↗