arXiv subjects

Xiang-Nan Zhou

Publications and source records attributed to Xiang-Nan Zhou.

12 recordsLinked to original sources

arXiv2023

Localization of $U(1)$ gauge field by non-minimal coupling with gravity

In this paper, we investigate the localization of the $U(1)$ gauge field on Randall-Sundrum-like braneworld models. The localization of the $U(1)$ gauge field is important because it plays a fundamental role in the branworld theories. To achieve the localization, we propose a novel action with a non-minimal coupling between the $U(1)$ gauge field and gravity. We find that the mass spectrum of the gauge field is continuous, without any gap between the zero-mass mode and the massive modes, and except for the zero-mass mode all the massive modes are not localized on the brane. Furthermore, the massive modes have negative squared masses, indicating they are tachyonic. Our analysis can be applied to a wide range of thin and thick braneworld scenarios, provided that the five-dimensional spacetime is asymptotically anti-de Sitter.

hep-th↗

arXiv2022

Restricted phase space thermodynamics of Einstein-power-Yang-Mills AdS black hole

We consider the thermodynamics of the Einstein-Power-Yang-Mills AdS black holes in the context of the gauge-gravity duality. Under this framework, the Newton's gravitational constant and the cosmological constant are varied in the system. We rewrite the thermodynamical first law in a more extended form containing both the pressure and the central charge of the dual conformal field theory, i.e., the restricted phase transition formula. A novel phenomena arises: the dual quantity of pressure is the effective volume, not the geometric one. That is leading to a new behavior of the Van de Waals-like phase transition for this system with the fixed central charge: the supercritical phase transition. From the Ehrenfest's scheme perspective, we check out the second-order phase transition of the EPYM AdS black hole. Furthermore the effect of non-linear Yang-Mills parameter on these thermodynamical properties is also investigated.

hep-th↗

arXiv2022

Shadow thermodynamics of non-linear charged Anti-de Sitter black holes

Non-linear interaction between the electromagnetic fields (EMF) are occurred when vacuum polarization in quantum electrodynamics (QED) happens. The field of non-linear electrodynamics which may be resulting from this interaction could have important effects on black hole physics. In this work, we investigate the relationship between the observable quantity, the shadow radius and the first-order phase transition for the non-linear charged AdS black hole in the frame of the Einstein-power-Yang-Mills (EPYM) gravity. Through the analysis, we find with a certain condition there exist the non-monotonic behaviors between the shadow radius, the horizon radius, and temperature (or pressure). And from the viewpoint of the shadow radius, the phase transition temperature is higher than that from the viewpoint of the horizon radius with the same condition. These indicate that the shadow radius can be regarded a probe to reveal the thermodynamic phase transition information of black holes. When the system is undergoing the phase transition in two cases of the different non-linear YM charge parameter values: $γ=1,~1.5$, the thermal profiles of the coexistent big and small black hole phases with the temperature are presented. Furthermore, the effects of non-linear YM charge parameter on the shadow radius and the thermal profile are also investigated.

hep-th↗

arXiv2019

Localization of five-dimensional Elko Spinors on dS/AdS Thick Branes

Different from the Dirac spinor, the localization of a five-dimensional Elko spinor on a brane with codimension one is very difficult because of the special structure of the Elko spinor. By introducing the coupling between the Elko spinor and the scalar field generating the brane, we have two mechanisms for localization of the zero mode of a five-dimensional Elko spinor on a brane. One is the Yukawa-type coupling and the other is the non-minimal coupling. In this paper, we investigate the localization of the Elko zero mode on de Sitter and Anti-de Sitter thick branes with the two localization mechanisms, respectively. It shows that both the mechanisms can realize the localization. The forms of the coupling functions of the scalar field in the two mechanisms have similar properties respectively and they play similar role for the localization.

hep-th↗

arXiv2018

Localization of Gravitino Field on $f(R)$ Thick Branes

In this paper, we consider the localization of a five-dimensional gravitino field on $f(R)$-thick branes. We obtain the coupled chiral equations of the Kaluza-Klein (KK) modes of gravitinos with the gauge condition $Ψ_z=0$. The chiral equations of a gravitino's KK modes are found to be almost identical to those of the Dirac fermion. However, their chiralities are exactly opposite. The chiral KK modes of gravitinos could be localized in some types of $f(R)$-thick branes on introducing a coupling term. We investigate the localization of a gravitino on three types of $f(R)$-thick branes through a Yukawa-like coupling term with background scalar fields. It has been shown that all the KK modes of gravitinos cannot be localized in the pure geometric $f(R)$-thick branes by adding a five-dimensional gravitino mass term. However, for the $f(R)$-thick branes generated by one or two background scalar fields, only the left- or right-handed zero mode could be localized in the branes, and the massive KK resonant modes are the same for both left- and right-handed gravitinos despite their opposing chiralities. All these results are consistent with those of the five-dimensional Dirac fermion except their chiralities, which may be an important sign to distinguish the gravitino field and the Dirac fermion field.

hep-th↗

arXiv2018

Localization of five-dimensional Elko spinors with non-minimal coupling on thick branes

It has been found that the zero mode of a five-dimensional Elko spinor could be localized on branes by introducing a Yukawa-type coupling between the Elko spinor and the background scalar field or the Ricci scalar. However, the Yukawa-type coupling is not appropriate for all brane models. In this paper, we explore other localization mechanism for the Elko spinor by introducing the non-minimal coupling $f(ϕ)\mathfrak{L}_{Elko}$ between the five-dimensional Elko spinor and the background scalar field. We give the general expressions of the Elko zero mode and the function $f(ϕ)$. Through two thick brane models and three concrete examples, we show that the Elko zero mode can be localized on the branes by this new mechanism. This provides us more possibilities of localizing the Elko zero mode.

hep-th↗

arXiv2017

Localization of Gravitino Field on Thin Branes

In this paper, we investigate the localization of a bulk gravitino field on the scalar-tensor branes and compare the result with that in the Randall-Sundrum-1 (RS1) model. The coupled chiral equations for the Kaluza-Klein (KK) modes of the gravitino field are obtained by fixing the gauge $Ψ_5=0$ and using the chiral KK decompositions. It is shown that, in the RS1 model for the left- and right-handed zero modes of the gravitino field, only one of them can be localized near one brane. For the massive modes, both chiral modes survive and the lower KK modes are localized near the IR brane from the four-dimensional physical coordinate point of view. However, for the scalar-tensor brane model, the localization of the gravitino chiral zero modes depends on the coupling parameter $λ$, and they will be not localized around anyone brane within a certain range of the parameter $λ$, which is quite different from the RS1 model. Furthermore, we also give the corresponding mass spectra of the massive KK gravitinos in the scalar-tensor model.

hep-th↗

arXiv2015

Shadow of noncommutative geometry inspired black hole

In this paper, the shadow casted by the rotating black hole inspired by noncommutative geometry is investigated. In addition to the dimensionless spin parameter $a/M_{0}$ with $M_{0}$ black hole mass and inclination angle $i$, the dimensionless noncommutative parameter $\sqrt{\vartheta}/M_{0}$ is also found to affect the shape of the black hole shadow. The result shows that the size of the shadow slightly decreases with the parameter $\sqrt{\vartheta}/M_{0}$, while the distortion increases with it. Compared to the Kerr black hole, the parameter $\sqrt{\vartheta}/M_{0}$ increases the deformation of the shadow. This may offer a way to distinguish noncommutative geometry inspired black hole from Kerr one via astronomical instruments in the near future.

gr-qc↗

arXiv2015

Localization and mass spectra of various matter fields on scalar-tensor brane

Recently, a new scalar-tensor braneworld model was presented in [Phys. Rev. \textbf{D 86} (2012) 127502]. It not only solves the gauge hierarchy problem but also reproduces a correct Friedmann-like equation on the brane. In this new model, there are two different brane solutions, for which the mass spectra of gravity on the brane are the same. In this paper, we investigate localization and mass spectra of various bulk matter fields (i.e., scalar, vector, Kalb-Ramond, and fermion fields) on the brane. It is shown that the zero modes of all the matter fields can be localized on the positive tension brane under some conditions, and the mass spectra of each kind of bulk matter field for the two brane solutions are different, which implies that the two brane solutions are not physically equivalent.

hep-th↗

arXiv2014

Dirac dynamical resonance states around Schwarzschild black holes

Recently, a novel kind of scalar wigs around Schwarzschild black holes---scalar dynamical resonance states were introduced in [Phys. Rev. D 84, 083008 (2011)] and [Phys. Rev. Lett. 109, 081102 (2012)]. In this paper, we investigate the existence and evolution of Dirac dynamical resonance states. First we look for stationary resonance states of a Dirac field around a Schwarzchild black hole by using the Schrödinger-like equations reduced from the Dirac equation in Schwarzschild spacetime. Then Dirac pseudo-stationary configurations are constructed from the stationary resonance states. We use these configurations as initial data and investigate their numerical evolutions and energy decay. These dynamical solutions are the so-called "Dirac dynamical resonance states". It is found that the energy of the Dirac dynamical resonance states shows an exponential decay. The decay rate of energy is affected by the resonant frequency, the mass of Dirac field, the total angular momentum, and the spin-orbit interaction. In particular, for ultra-light Dirac field, the corresponding particles can stay around a Schwarzschild black hole for a very long time, even for cosmological time-scales.

gr-qc↗

arXiv2012

Localization of 5D Elko Spinors on Minkowski Branes

Recently, a new spin-1/2 fermionic quantum field with mass dimension one in four dimensions--Elko field $λ$ was introduced as a candidate of dark matter. In this paper, we investigate the localization of 5D Elko {spinors} on Minkowski branes by presenting the equation of {the} Elko KK modes. For the 5D free massless Elko field, the zero mode can be localized on Randall-Sundrum thin brane but can not be localized on the majority of thick branes. There {do} not exist bound massive KK modes on all these branes. If the 5D mass term is introduced, there will exist bound Elko zero mode in Randall-Sundrum brane model. And when we introduce the Yukawa type coupling $ηϕ^2 \mathop λ\limits^\negλ$ with $ϕ$ the background scalar field, the Elko zero mode can be localized on some special thick branes with a particular coupling constant $η$. Nevertheless, the massive KK modes still can not be localized on these branes. These results are very different from that of the conventional Dirac spinor {field} and the scalar field.

hep-th↗

arXiv2012

Non-minimal Coupling Branes

We study a thick and Z_2 symmetric braneworld model with a non-minimally coupled bulk scalar. Several analytic solutions are found. There are two categories of the brane configuration: standard branes and deformed ones. The former is just the same with the solutions in general relativity, whereas the latter has negative effective energy densities in the location of the branes. The question of stability under metric tensor perturbation is also investigated, and there is no tachyon. We show that the gravity zero mode (namely the 4D massless graviton) is the only one state that can be localized on the branes. So Newtonian potential can be recovered in 4D space-time.

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