arXiv subjects

Tian-Chi Ma

Publications and source records attributed to Tian-Chi Ma.

11 recordsLinked to original sources

arXiv2026

Dynamics of kinks in a traversable wormhole

We investigate the dynamics of spherically symmetric radial domain walls (or kinks) in a traversable Simpson-Visser wormhole. By solving the scalar field in a double-well potential, we find that the parameter $a$ has a strong impact on the kink dynamics: larger $a$ allows the kink to go through the throat back and forth, while smaller $a$ strongly confines the kink nearby the throat. In addition, each traverse of the kink through the throat is accompanied with the emission of scalar wave packets, resulting in a gradual decrease of the oscillation amplitude reminiscent of a damping oscillator. This oscillatory behavior between the two sides of the wormhole is in sharp contrast to its counterpart in compact objects, such as boson stars. Our findings uncover how wormhole geometry will influence the dynamics of topological defects and may provide new insights for distinguishing wormholes from ordinary compact objects.

gr-qc↗

arXiv2026

Radial kinks in the boson stars

In this work, we study the time evolution of radial kinks in the background of boson stars. In particular, we consider two types of boson stars: the massive boson star and the solitonic boson star. For each boson star, we study the dynamics of the kinks with four different compactnesses. We observe that the greater the compactness is, the slower the kinks move towards the origin of the boson stars, indicating that the compactness will hinder the kinks to collide with the origin. Additionally, it is found that when the boson star is highly compact, a new kink may turn out after the kink colliding with the origin, instead of immediately dissipating into the background. We then propose that the radial kinks may potentially serve as a means to probe the internal structures of dense astrophysical objects, even the interior structure of black holes.

gr-qc↗

arXiv2025

Quasinormal modes and greybody factor of charged black hole in non-commutative geometry

In this article, the quasinormal modes and greybody factor of charged black hole in non-commutative geometry are studied. Under the assumption of a uniformly distributed charge within the matter, we obtain the metric for a charged black hole in non-commutative geometry. We calculated the wave function and obtained the effective potential of three different perturbed fields with spin. Then we applied $6^{\rm{th}}$ order WKB method to analyze the quasinormal modes of the black hole and derived quasinormal frequencies. Futhermore, we discussed the greybody factor in different perturbed fields under this spacetime.

gr-qc↗

arXiv2024

Universal Critical Holography and Domain Wall Formation

Using holography, we study the universal scaling laws governing the coarsening dynamics of strongly coupled domain walls. Specifically, we studied the universal dependence of the length of the domain wall interfaces on the quench rate. The relation satisfies the Kibble-Zurek scaling shortly after the critical point. However, as time goes by, the coarsening dynamics suppresses the Kibble-Zurek scaling in favor of a universal dynamical scaling of the characteristic length and the adiabatic growth of the system. Theoretical predictions of the universal scaling laws are consistent with numerical findings in both regimes for both weak and strongly coupled systems.

cond-mat.stat-mech↗

arXiv2024

Asymmetric Symmetry Breaking: Unequal Probabilities of Vacuum Selection

Spontaneous symmetry breaking is a fundamental notion in modern physics, ranging from high energy to condensed matter. However, the usual spontaneous symmetry breaking only considers the equal probability to select the vacua. In this work, we conceive a model to realize the unequal probability of the symmetry breaking, leading to an unbalanced number of ground states. Specifically, we study the probabilities of a scalar field to roll down from the top of a potential, where the top is only $C^1$ continuous. As the whole system is subject to random perturbations, we find that the probability for the field to roll down to the left or right side depends the square root of the second derivative of the potential at the top. We solve this problem theoretically by using the Fokker-Planck equations in stochastic process and verify our findings numerically. This study may potentially be a new mechanism to explain the origins of asymmetries in the Universe.

hep-th↗

arXiv2024

Topologically Protected Metastable States in Classical Dynamics

We propose that domain walls formed in a classical Ginzburg-Landau model can exhibit topologically stable but thermodynamically metastable states. This proposal relies on Allen-Cahn's assertion that the velocity of domain wall is proportional to the mean curvature at each point. From this assertion we speculate that domain wall behaves like a rubber band that can winds the background geometry in a nontrivial way and can exist permanently. We numerically verify our proposal in two and three spatial dimensions by using various boundary conditions. It is found that there are possibilities to form topologically stable domain walls in the final equilibrium states. However, these states have higher free energies, thus are thermodynamically metastable. These metastable states that are protected by topology could potentially serve as storage media in the computer and information technology industry.

cond-mat.stat-mech↗

arXiv2023

Shadow of Schwarzschild Black Hole in the Cold Dark Matter Halo

The Schwarzschild black hole in the Cold Dark Matter (CDM) halo is studied, and the radiation laws of the thin accretion disk near the black hole are discussed and summarized. The orbits of light around the black hole are also calculated. Additionally, using the Novikov-Thorne model's light intensity function of the thin accretion disk, it is possible to solve for the shadow created by the thin accretion disk near the Schwarzschild black hole as well as the observed luminosity of the disk.

gr-qc↗

arXiv2021

Coexistence of Type-II and Type-IV Dirac Fermions in SrAgBi

Relativistic massless Weyl and Dirac fermions have isotropic and linear dispersion relations to maintain Poincaré symmetry, which is the most basic symmetry in high-energy physics. The situation in condensed matter physics is less constrained; only certain subgroups of Poincaré symmetry -- the 230 space groups that exist in 3D lattices -- need be respected. Then, the free fermionic excitations that have no high energy analogues could exist in solid state systems. Here, We discovered a type of nonlinear Dirac fermion without high-energy analogue in SrAgBi and named it type-IV Dirac fermion. The type-IV Dirac fermion has a nonlinear dispersion relationship and is similar to the type-II Dirac fermion, which has electron pocket and hole pocket. The effective model for the type-IV Dirac fermion is also found. It is worth pointing out that there is a type-II Dirac fermion near this new Dirac fermion. So we used two models to describe the coexistence of these two Dirac fermions. Topological surface states of these two Dirac points are also calculated. We envision that our findings will stimulate researchers to study novel physics of type-IV Dirac fermions, as well as the interplay of type-II and type-IV Dirac fermions.

cond-mat.mtrl-sci↗

arXiv2021

Shadow cast by a rotating and nonlinear magnetic-charged black hole in perfect fluid dark matter

We derived an exact solution of the spherically symmetric Hayward black hole surrounded by perfect fluid dark matter (PFDM). By applying the Newman-Janis algorithm, we generalized it to the corresponding rotating black hole. Then, we studied the shadows of rotating Hayward black hole in PFDM. The apparent shape of the shadow depends upon the black hole spin $a$, the magnetic charge $Q$ and the PFDM intensity parameter $k$ ($k<0$). The shadow is a perfect circle in the non-rotating case ($a=0$) and a deformed one in the rotating case ($a\neq{0}$). For a fixed value of $a$, the size of the shadow increases with the increasing $\vert{k}\vert$, but decreases with the increasing $Q$. We further investigated the black hole emission rate. We found that the emission rate decreases with the increasing $\vert{k}\vert$ (or $Q$) and the peak of the emission shifts to lower frequency. Finally, we discussed the observational prospects corresponding to the supermassive black hole $\mathrm{Sgr\ A^{*}}$ at the center of the Milky Way.

gr-qc↗

arXiv2021

Bardeen black hole surrounded by perfect fluid dark matter

We derive an exact solution of the spherically symmetric Bardeen black hole surrounded by perfect fluid dark matter (PFDM). By treating the magnetic charge $g$ and dark matter parameter $α$ as thermodynamic variables, we find that the thermodynamic first law and the corresponding Smarr formula are satisfied. The thermodynamic stability of the black hole is also studied. The result show that, there exists a critical radius $r_{+}^{C}$, where the heat capacity diverges, suggesting that the black hole is thermodynamically stable in the range $0<r_{+}<r_{+}^{C}$. In addition, the critical radius $r_{+}^{C}$ increases with the magnetic charge $g$ and decreases with the dark matter parameter $α$. Applying the Newman-Janis algorithm, we generalize the spherically symmetric solution to the corresponding rotating black hole. With the metric at hand, the horizons and ergospheres are studied. It turns out that for a fixed dark matter parameter $α$, in a certain range, with the increase of the rotation parameter $a$ and magnetic charge $g$, the Cauchy horizon radius increases while the event horizon radius decreases. Finally, we investigate the energy extraction by the Penrose process in rotating Bardeen black hole surrounded by PFDM.

gr-qc↗

arXiv2020

Optical properties of a nonlinear magnetic charged rotating black hole surrounded by quintessence with a cosmological constant

In this paper,we discuss optical properties of the nonlinear magnetic charged black hole surrounded by quintessence with a non-zero cosmological constant $Λ$. Setting the state parameter $ω=-3/2$ , we studied the horizon, the photon region and the shadow of this black hole. It turned out that for a fixed quintessential parameter $γ$, in a certain range, with the increase of the rotation parameter $a$ and magnetic charge $Q$, the inner horizon radius increases while the outer horizon radius decreases. And the cosmological horizon $r_Λ$ decrease when $γ$ or $Λ$ incease and increase slightly with increasing $a$ and $Q$. The shapes of photon region were then studied and depicted through graphical illustrations. Finally, we discussed the effects of the quintessential parameter $γ$ and the cosmological constant $Λ$ on the shadow cast by this balck hole with a fixed observer position.

gr-qc↗