arXiv subjects

Yong-Qiang Wang

Publications and source records attributed to Yong-Qiang Wang.

At least 55 records · Page 3Linked to original sources

arXiv2023

Building a black hole-wormhole-black hole combination

In this paper, we present the spherically symmetric Proca star in the presence of a phantom field and obtain a traversable wormhole solution for non-trivial topological spacetime. Using numerical methods, symmetric solutions and asymmetric solutions are obtained in two asymptotically flat regions. We find that when changing the throat size $r_{0}$, both the mass $M$ and the Noether charge $Q$ no longer have the spiral characteristics of an independent Proca star, furthermore, the asymmetric solution can be turned into the symmetric solution at some frequency $ω$ in certain $r_{0}$. In particular, we find that when the frequency takes a certain value, for each solution, there is an extremely approximate black hole solution, and there is even a case where an event horizon appears on both sides of the wormhole throat.

gr-qc↗

arXiv2023

$κ$-Dirac stars

In this paper, we construct a Dirac star model composed of $|κ|$ pairs of spinor fields. The azimuthal harmonic indeces $m$ of these spinor fields are half-integers, and they satisfiy $-(|κ|-\frac{1}{2})\leq m \leq |κ|-\frac{1}{2}$. When $κ=1$, it corresponds to the conventional Dirac star model, formed by two spinor fields with $m=\frac{1}{2}$ and $m=-\frac{1}{2}$. When $|κ|>1$, among these $|κ|$ pairs of spinor fields, there exist spinor fields with azimuthal harmonic indices $m>\frac{1}{2}$, and all spinor fields still conform to the same Dirac field equation. Different families of solutions are distinguished by the value of $κ$, so we named these solutions $κ$-Dirac stars. We obtain solutions for $κ=\pm1,\pm2,\pm3,\pm4,\pm5,\pm6$ by using numerical methods. Additionally, we compute their ADM mass $M$, Noether charge $Q$, and binding energy $E$, and illustrate how these quantities change with the spinor field's frequency $ω$ for different $κ$. We observe significant differences between solutions for $|κ|>1$ and the $|κ|=1$ case. Furthermore, we provide the energy density distribution of the Dirac stars, wherein for $|κ|>1$ scenarios, the Dirac stars exhibit a spherical shell-like structure. Moreover, we employ three-dimensional diagrams to intuitively depict how $κ$ influences the combination of spinor fields to form a spherically symmetric configuration.

gr-qc↗

arXiv2023

Tidal Love numbers of Axion stars

We investigate the tidal deformability of spherically symmetric axion stars on the stable branches, including the Newtonian and relativistic branches. The results suggest that on the stable branch, the electric Love numbers of axion star are positive, while the magnetic Love numbers are negative. On the Newtonian stable branch, the electric tidal Love numbers are much larger than the magnetic ones, while on the relativistic stable branch, they are slightly larger. Furthermore, the relativistic stable branch has much smaller tidal Love numbers than the Newtonian stable branch, indicating weaker deformability of axion stars on the relativistic stable branch. This could be attributed to the fact that on the relativistic branch, axion stars are more compact, resulting hardly distorted by tidal forces.

gr-qc↗

arXiv2023

Emergency of black holes from wormholes

In this paper, we study the spherically symmetric Dirac star model in the presence of a phantom field, obtaining a traversable wormhole solution in non-trivial topological spacetime. This solution exhibits asymmetry in both the field configuration and the metric and possesses a finite ADM mass $M$ and Noether charge $Q$. Furthermore, we find that due to the presence of a wormhole at the center, this solution exhibits many differences from the Dirac star under trivial spacetime. Notably, when the wormhole throat size is small, our numerical calculations indicate the emergence of an extremely approximate black hole solution on one side of the wormhole spacetime, a phenomenon unexplored. At this time, the Kretschmann scalar near the throat tends to infinity, indicating the wormhole becomes untraversable.

gr-qc↗

arXiv2023

Excited Dirac stars with higher azimuthal harmonic index

In this paper, we investigate the properties of the first excited state Dirac stars (DSs) with higher azimuthal harmonic index (specifically, the azimuthal harmonic indexes $m_D$ = $3/2$, $5/2$, $7/2$), as well as the relationship between the ADM mass and angular momentum of Dirac stars with respect to frequency. Moreover, We find that the ergospheres of DSs appear at lower spinor field frequencies, and both the ergospheres and the distribution of the spinor field functions are asymmetric about the equatorial plane. Furthermore, we introduce the ground state scalar field and examine its impact on this system, which is known as the multi-state Dirac-boson stars (DBSs) model. We show various types of solution families for DBSs under both synchronized frequency $ω$ and nonsynchronized frequencies and find that similar to DSs, the spinor field and the ergospheres of DBSs are also asymmetric about the equatorial plane, but the ergospheres appear at higher spinor field frequencies.

gr-qc↗

arXiv2023

Dirac-Proca stars

We consider a model consists of the Einstein gravity in four-dimensional spacetime, a Proca field and two Dirac fields through minimum coupling. By numerically solving this model, we obtain two types of solutions: synchronized frequency solutions and non-synchronized frequency solutions. We find that in the case of two kinds of matter fields, different families of solutions can be obtained in both synchronized and non-synchronized frequency cases, and the two families can shift to each other when certain parameters are changed. Moreover, we calculate the binding energy of multi-field solutions and give the relationship between binding energy $E$ and synchronized frequency $\tildeω$ (non-synchronized frequency $\tildeω_P$), so as to analyze the stability of the corresponding family.

gr-qc↗

arXiv2023

Rotating multistate axion boson stars

We consider excited configuration and multistate configuration of rotating axion boson stars~(RABSs).RABSs are asymptotically flat, stationary, spinning, horizonless solutions of Einstein-Klein-Gordon theory in which the scalar potential depends on scalar field mass $μ$ and axion decay constant $f_a$. The excited RABSs have two types of solutions, including $^2S$ state and $^2P$ state. The rotating multistate axion boson stars~(RMABSs) consist of coupled fundamental configuration and excited configuration, and also include two types of solutions: $^1S^2S$ state and $^1S^2P$ state. Some differences between RABSs models and rotating mini-boson stars models are discussed. We show the solution space of these models for different values of decay constant $f_a$. We found fundamental RABSs have a higher maximum mass than the excited state in the low decay constant region. Moreover, the multistate configuration allows a higher mass than both the fundamental configuration and the excited configuration at the same frequency. We also found the RMABSs have the second branch in which the ergo-region emerges. This means the second branch may be superradiant unstable.

gr-qc↗

arXiv2023

Multi-state Dirac stars

In this paper, we construct the multi-state Dirac stars (MSDSs) consisting of two pairs of Dirac fields. The two pairs of Dirac fields are in the ground state and the first excited state, respectively. Each pair consists of two fields with opposite spins, ensuring spherical symmetry of the system. We discuss the solutions of the MSDSs under synchronized and nonsynchronized frequencies. By varying the mass $\tildeμ_1$ of the excited state Dirac field and the frequency $\tildeω_0$ of the ground state Dirac field, we obtain different types of solutions, including single-branch and double-branch solutions. These two types of solutions do not smoothly transition into each other as the parameters $\tildeμ_1$ and $\tildeω_0$ continuously change, but undergo a sudden transition when $\tildeμ_1$ ($\tildeω_0$) is greater than or less than the threshold value of $0.7694$ ($0.733$). Furthermore, we analyze the characteristics of the various MSDSs solutions and analyze the relationship between the ADM mass $M$ of the MSDSs and the synchronized and nonsynchronized frequencies. Subsequently, we calculate the binding energy $E_B$ of the MSDSs and discuss the stability of the solutions. Finally, we discuss the feasibility of simulating the dark matter halos using MSDSs.

hep-th↗

arXiv2023

Study of Boson Stars with Wormhole

In this paper, we reconsider the mixed system of BSs with wormholes at their center which performed by complex scalar field and phantom field and study a whole new condition about the potential. Both the symmetric and asymmetric solutions in the two asymptotically flat regions are obtained by using numerical method and we mainly explore the change of the results by varying the parameters of throats and potential. In ground state, we find there are multiple solutions at certain setting of parameters and with the increase of $η_0$ or decrease of $c$, the results gradually become single-valued functions and these two variables have similar influence to the curve shape of mass $M$ and charge $Q$, furthermore, the asymmetric solutions can turn into the solutions of symmetry at some frequency $ω$ in certain $η_0$ and $c$. However, when it comes to excited state, the properties of solutions of symmetry is similar to the ground state while asymmetrical results exhibit altered characteristics. We also present the geometries of wormhole to investigate the property of this model.

gr-qc↗

arXiv2023

Boson star with parity-odd symmetry in wormhole spacetime

In this paper, we revisit the model of bosonic matter in the form of a free complex scalar field with a nontrivial wormhole spacetime topology supported by a free phantom field. We obtain a new type of boson star with wormhole solutions, in which the complex scalar field possess full parity-odd symmetry with respect to the two asymptotically flat spacetime regions. When the size of the throat is small, The behavior of boson stars with wormhole approaches that of boson stars. When the size of the throat is intermediate, the typical spiraling dependence of the mass and the particle number on the frequency of the boson stars is replaced by a loop structure. However, as the size becomes relatively large, the loop structure will also disappear. In particular, The complex scalar field could form two boson stars with opposite phase differences with respect to the two spacetime regions in the limit of vanishing throat size. We analyze the properties of this new type of boson stars with wormhole and further show that the wormhole spacetime geometry.

gr-qc↗

arXiv2023

Hybrid Proca-boson stars

In this paper, we construct a hybrid boson star model that contains a complex scalar field and a Proca field. The scalar field is in the ground state, while the Proca field is in the first excited state. We numerically solve the model and obtain solution families of different coexisting states by considering both synchronized and nonsynchronized cases. By examining the relation between ADM mass and synchronized frequency $\tildeω$ or nonsynchronized frequency $\tildeω_P$, we identify several types of solution families for the hybrid boson stars. In addition to solutions that intersect the scalar field and the Proca field at each end, there are also several types of multi-branch coexisting state solutions. The characteristics of various solutions are analyzed and discussed in detail. We calculate the binding energy $E$ of the hybrid Proca-boson stars and provide the relationship between $E$ and both synchronized frequency $\tildeω$ and nonsynchronized frequency $\tildeω_P$. Furthermore, we obtain the stability of the corresponding hybrid star solution families from these analyses above.

gr-qc↗

arXiv2022

Chains of mini-boson stars

In this paper, we re-investigate the stationary, soliton-like solutions in the model of the Einstein gravity coupled to a free and complex scalar field, which have been known as mini-boson stars. With numerical method, we find that in addition to the usual single mini-boson star solution, there exist a novel family of solutions interpreted as chains of boson stars, which is made of some boson stars along the symmetry axis. We show the configuration of two types of chains, including an even number of constituents and an odd number of constituents. Furthermore, we also study the effect of the frequency of the complex scalar field on the ADM mass $M$ and the $U(1)$ scalar charge $Q$. It is interesting to note that the existence of chains of boson stars does not require the introduction of a complex scalar field with self-interacting potential.

gr-qc↗

arXiv2022

Equatorial orbits of spinning test particle in rotating boson star

In this paper, we study the circular orbit of the spinning test particle in the background of a rotating boson star. Using the pole-dipole approximation and neglecting the back-reaction of the spinning test particle on the spacetime, the equation of motion of the spinning test particle is described by the Mathisson-Papapetrou-Dixon equation. We solve this equation under the Tulczyjew spin-supplementary condition and obtain the four-momentum and four-velocity of the spinning test particle. Quite different from the spinless particle, the effective potential of the spinning particle with zero orbital angular momentum goes to infinite at the center of the rotating boson star. This will lead to the fact that the spinning particle can not pass through the center of the boson star. However, when the spin angular momentum and orbital angular momentum satisfy $2\bar{s}+\bar{l}=0$, the effective potential is not divergent anymore and the spinning particle can pass through the center of the rotating boson star. {We still investigate how the spin affects the structure of the circular orbits and we find that the spin will induce the larger or smaller regions of no circular orbits, unstable circular orbits, and stable circular orbits.} Moreover, the radius and energy of the circular orbit will be decreased or increased by the particle spin. These results will have an important application in testing the gravitational waves in the boson star background.

gr-qc↗

arXiv2022

Dynamics of scalar hair with self-interactions around a Schwarzchild black hole

In this paper, we study the dynamics of scalar hair around a Schwarzchild black hole. The scalar hair is sourced by the Gauss-Bonnet invariant with a linear coupling. We work perturbatively in the coupling constant and ignore the back-reaction of the scalar hair and the Gauss-Bonnet invariant. We evolve the scalar field in the background of a Schwarzchild black hole and study the dynamical formation of scalar hair with different self-interactions. We integrate the energy and compute the energy flux of the scalar hair in terms of the canonical energy-momentum tensor and give the corresponding dependence on the self-interactions. Our results allow us to estimate the radiation and the condensation of scalar field with different self-interactions, these would improve our understanding for the dynamical scalarization of black holes and the possible configuration of the scalar hair in scalar Gauss-Bonnet gravity.

gr-qc↗

arXiv2022

Weak cosmic censorship with $SU(2)$ gauge field and bound on charge-to-mass ratio

We numerically construct the stationary solutions of $SU(2)$ Einstein-Yang-Mills theory in four dimensional anti-de Sitter spacetime. When the $t$ component of $SU(2)$ gauge field is taken to the only nonzero component, we construct a class of counterexamples to the weak cosmic censorship conjecture in Einstein-Maxwell theory. However, including a nonzero $ϕ$ component of $SU(2)$ gauge field, we can argue that there is a minimum value $q_W$, when the charge carried by the $ϕ$ component is larger than this minimum value, for sufficiently large boundary electric amplitude $a$, the original counterexamples can be removed and cosmic censorship is preserved.

hep-th↗

arXiv2022

Dirac-boson stars

In this paper, we construct \textit{Dirac-boson stars} (DBSs) model composed of a scalar field and two Dirac fields. The scalar field and both Dirac fields are in the ground state. We consider the solution families of the DBSs for the synchronized frequency $\tildeω$ and the nonsynchronized frequency $\tildeω_D$ cases, respectively. We find several different solutions when the Dirac mass $\tildeμ_D$ and scalar field frequency $\tildeω_S$ are taken in some particular ranges. In contrast, no similar case has been found in previous studies of multistate boson stars. Moreover, we discuss the characteristics of each type of solution family of the DBSs and present the relationship between the ADM mass $M$ of the DBSs and the synchronized frequency $\tildeω$ or the nonsynchronized frequency $\tildeω_D$. Finally, we calculate the binding energy $E_B$ of the DBSs and investigate the relationship of $E_B$ with the synchronized frequency $\tildeω$ or the nonsynchronized frequency $\tildeω_D$.

gr-qc↗

arXiv2022

Spontaneously translational symmetry breaking in the excited states of holographic superconductor

We revisit HHH model in [Phys. Rev. Lett. {\bf 101}, 031601 (2008)] and extend the ansatz of matter fields to being of depending on a spatial dimension except the holographic direction. Despite homogeneous solutions of ground and excited states, especially for the excited states, there also exists solutions where the translational invariance is broken. It is worth mentioning that no periodic sources are assigned to the matter fields, so the translational symmetry is broken spontaneously. We investigate how the new solutions and the condensates of excited states develop with the change of temperature. Moreover, since this kind of condensate will decrease at certain temperature and eventually vanish at sufficiently low temperature, we also study the relation between this interval and length of lattice. Besides, we compare the free energies of non-translational invariant solutions and those of translational invariance in the HHH model, and find that the free energies of the former situations are lower.

hep-th↗

arXiv2022

Comment on ''Traversable Wormholes in General Relativity''

In the letter titled ''Traversable Wormholes in General Relativity'' [Phys. Rev. Lett. 128, 091104 (2022)], R. A. Konoplya and A. Zhidenko have constructed an asymmetric wormhole solution, which is not symmetric about the throat and is compounded from smooth gravitational and charged Dirac fields. However, the authors have claimed that a physically relevant condition on the throat is imposed to lead to no gravitational force experienced by a stationary observer at the throat. In this comment, we point out that the above condition is unnecessary.

gr-qc↗