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Zhen-Hua Zhao

Publications and source records attributed to Zhen-Hua Zhao.

36 records · Page 2Linked to original sources
arXiv2013

Non-perturbative procedure for stable $K$-brane

We propose a novel first-order formalism for a type of $K$-brane systems. An example solution is presented and studied. We illustrate how the noncanonical kinetic term can affect the properties of the model, such as the stability of the solutions, the localization of fermion and graviton. We argue that our solution is stable against linear perturbations. The tensor zero mode of graviton can be localized while the scalar zero mode cannot. The localization condition for fermion is also discussed.

hep-th↗
arXiv2012

Thick branes with a nonminimally coupled bulk-scalar field

In this paper, we investigate thick branes with a nonminimally coupled background scalar field, whose solution is a single-kink or a double-kink. The effects of the nonminimal coupling constant $ξ$ on the structure of the thick branes and the localization of gravity, fermions, scalars and vectors are discussed. It is shown that each brane will split into two sub-branes as increasing the nonminimal coupling constant $ξ$. By investigating the tensor perturbation equations of gravity and the general covariant Dirac equation of fermions, we find that both the gravity zero mode and left-chiral fermion zero mode are localized at the center of the single-kink branes and localized between the two sub-branes generated by the double-kink, which indicates that the constant $ξ$ does not effect the localization of these zero modes. However, the zero mode of scalars is localized on each sub-brane (for both single-kink and double-kink branes) when $ξ$ is larger than its critical value $ξ_0$. The effects of the nonminimal coupling constant $ξ$ on the resonances of gravity and fermions with finite lifetime on the branes are also discussed.

hep-th↗
arXiv2011

Holographic p-wave Josephson junction

In this work we generalized holographic model for s-wave DC Josephson junction constructed in arXiv:1101.3326[hep-th] to a holographic description for p-wave Josephson junction. By solving numerically the coupled equations of motion of Yang-Mills theory for a non-Abelian SU(2) gauge fields in (3+1)-dimensional AdS spacetimes, we shown that DC current of the p-wave Josephson junction is proportional to the sine of the phase difference across the junction like the s-wave case.

hep-th↗
arXiv2011

Domain wall brane in squared curvature gravity

We suggest a thick braneworld model in the squared curvature gravity theory. Despite the appearance of higher order derivatives, the localization of gravity and various bulk matter fields is shown to be possible. The existence of the normalizable gravitational zero mode indicates that our four-dimensional gravity is reproduced. In order to localize the chiral fermions on the brane, two types of coupling between the fermions and the brane forming scalar is introduced. The first coupling leads us to a Schrödinger equation with a volcano potential, and the other a Pöschl-Teller potential. In both cases, the zero mode exists only for the left-hand fermions. Several massive KK states of the fermions can be trapped on the brane, either as resonant states or as bound states.

hep-th↗
arXiv2011

Effects of temperature on thick branes and the fermion (quasi-)localization

Following Campos's work [Phys. Rev. Lett. 88, 141602 (2002)], we investigate the effects of temperature on flat, de Sitter (dS), and anti-de Following Campos's work [Phys. Rev. Lett. \textbf{88}, 141602 (2002)], we investigate the effects of temperature on flat, de Sitter (dS), and anti-de Sitter (AdS) thick branes in five-dimensional (5D) warped spacetime, and on the fermion (quasi-)localization. First, in the case of flat brane, when the critical temperature reaches, the solution of the background scalar field and the warp factor is not unique. So the thickness of the flat thick brane is uncertain at the critical value of the temperature parameter, which is found to be lower than the one in flat 5D spacetime. The mass spectra of the fermion Kaluza-Klein (KK) modes are continuous, and there is a series of fermion resonances. The number and lifetime of the resonances are finite and increase with the temperature parameter, but the mass of the resonances decreases with the temperature parameter. Second, in the case of dS brane, we do not find such a critical value of the temperature parameter. The mass spectra of the fermion KK modes are also continuous, and there is a series of fermion resonances. The effects of temperature on resonance number, lifetime, and mass are the same with the case of flat brane. Last, in the case of AdS brane, {the critical value of the temperature parameter can less or greater than the one in the flat 5D spacetime.} The spectra of fermion KK modes are discrete, and the mass of fermion KK modes does not decrease monotonically with increasing temperature parameter.

hep-th↗
arXiv2011

Holographic Josephson Junction in 3+1 dimensions

In arXiv:1101.3326[hep-th], a (2+1)-dimensional holographic Josephson junction was constructed, and it was shown that the DC Josephson current is proportional to the sine of the phase difference across the junction. In this paper, we extend this study to a holographic description for the (3+1)-dimensional holographic DC Josephson junction. By solving numerically the coupled differential equations, we also obtain the familiar characteristics of Josephson junctions.

hep-th↗
arXiv2011

Fermion Resonances on a Thick Brane with a Piecewise Warp Factor

In this paper, we mainly investigate the problems of resonances of massive KK fermions on a single scalar constructed thick brane with a piecewise warp factor matching smoothly. The distance between two boundaries and the other parameters are determined by one free parameter through three junction conditions. For the generalized Yukawa coupling $η\barΨϕ^{k}Ψ$ with odd $k=1,3,5,...$, the mass eigenvalue $m$, width $Γ$, lifetime $τ$, and maximal probability $P_{max}$ of fermion resonances are obtained. Our numerical calculations show that the brane without internal structure also favors the appearance of resonant states for both left- and right-handed fermions. The scalar-fermion coupling and the thickness of the brane influence the resonant behaviors of the massive KK fermions.

hep-th↗
arXiv2011

Area spectrum of Schwarzschild black hole inspired by noncommutative geometry

It is known that, in the noncommutative Schwarzschild black hole spacetime, the point-like object is replaced by the smeared object, whose mass density is described by a Gaussian distribution of minimal width $\sqrtθ$ with $θ$ the noncommutative parameter. The elimination of the point-like structures makes it quite different from the conventional Schwarzschild black hole. In this paper, we mainly investigate the area spectrum and entropy spectrum for the noncommutative Schwarzschild black hole with $0\leq θ\leq (\frac{M}{1.90412})^{2}$. By the use of the new physical interpretation of the quasinormal modes of black holes presented by Maggiore, we obtain the quantized area spectrum and entropy spectrum with the modified Hod's and Kunstatter's methods, respectively. The results show that: (1) The area spectrum and entropy spectrum are discrete. (2) The spectrum spacings are dependent on the parameter $\frac{M}{\sqrtθ}$. (3) The spacing of the area spectrum of the noncommutative Schwarzschild black hole is smaller than that of the conventional one. So does the spacing of the entropy spectrum. (4) The spectra from the two methods are consistent with each other.

hep-th↗
arXiv2010

Bulk Matters on a GRS-Inspired Braneworld

In this paper we investigate the localization and mass spectra of bulk matter fields on a Gergory-Rubakov-Sibiryakov-inspired braneworld. In this braneworld model, there are one thick brane located at the origin of the extra dimension and two thin branes at two sides. For spin 1/2 fermions coupled with the background scalar $ϕ$ via $η\barΨϕ^pΨ$ with $p$ a positive odd integer, the zero mode of left-hand fermions can be localized on the thick brane for finite distance of the two thin branes, and there exist some massive bound modes and resonance modes. The resonances correspond to the quasi-localized massive fermions. For free massless spin 0 scalars, the zero mode can not be localized on the thick brane when the two thin branes are located finitely. While for a massive scalar $Φ$ coupled with itself and the background scalar field $ϕ$, in order to get a localized zero mode on the thick brane, a fine-tuning relation should be introduced. Some massive bound modes and resonances also will appear. For spin 1 vectors, there is no bound KK mode because the effective potential felt by vectors vanishes outside the two thin branes. We also investigate the physics when the distance of the two thin branes tends to infinity.

hep-th↗
arXiv2010

Effects of the variation of mass on fermion localization and resonances on thick branes

A few years ago, Campos investigated the critical phenomena of thick branes in warped spacetimes [Phys. Rev. Lett. {\bf 88} (2002) 141602]. Inspired by his work, we consider a toy model of thick branes generated by a real scalar field with the potential $V(ϕ)=aϕ^2-bϕ^4+cϕ^6$, and investigate the variation of the mass parameter $a$ on the branes as well as the localization and resonances of fermions. An interesting result is found: there is a critical value for the mass parameter $a$, and when the critical value of $a$ is reached the solution of the background scalar field is not unique and has the shape of a double kink. This happens in both cases with and without gravity. It is also shown that the numbers of the bound Kaluza-Klein modes of fermions on the gravity-free brane and the resonant states of fermions on the brane with gravity increase with the value of $a$.

hep-th↗
arXiv2010

Fermion localization on asymmetric two-field thick branes

In this paper we investigate the localization of fermions on asymmetric thick branes generated by two scalars $ϕ$ and $χ$. In order to trap fermions on the asymmetric branes with kink-like warp factors, the couplings with the background scalars $η\barΨF(χ,ϕ)Ψ$ are introduced, where $F(χ,ϕ)$ is a function of $ϕ$ and $χ$. We find that the coupling $η\barΨχϕΨ$ do not support the localization of 4-dimensional fermions on the branes. While, for the case $η\barΨχΨ+η'\barΨϕΨ$, which is the kink-fermion coupling corresponding to one-scalar-generated brane scenarios, the zero mode of left-handed fermions could be trapped on the branes under some conditions.

hep-th↗
arXiv2009

Fermion Resonances on Multi-field Thick Branes

Motivated by the recent work on the fermion resonances on scalar-constructed thick branes (arXiv:0901.3543 and arXiv:0904.1785), we extend the idea to multi-scalar generated thick branes and complete previous work. The fermion localization and resonances on the three-field and two-field thick branes are investigated. With the Numerov method, our numerical results show that the resonance states also exist in the brane besides the single-field thick branes and the two-field thick branes in the former cases. This interesting phenomenon is related to the internal structure of the brane and the coupling of fermions and scalars. We find that the Kaluza-Klein chiral decomposition of massive fermion resonances is the parity-chiral decomposition. For the couplings $η\barΨϕ^{k}χρΨ$ and $η\barΨϕ^{k}χρΨ$ for three-field and two-field models with odd positive $k$, respectively, the number of the resonant states decreases with $k$. This result is opposite to the one obtained in the single-field de Sitter thick brane (arXiv:0904.1785).

hep-th↗
arXiv2009

Fermion Localization and Resonances on A de Sitter Thick Brane

In arXiv:0901.3543, the simplest Yukawa coupling $η\barΨϕχΨ$ was considered for a two-scalar-generated Bloch brane model. Fermionic resonances for both chiralities were obtained, and their appearance is related to branes with internal structure. Inspired on this result, we investigate the localization and resonance spectrum of fermions on a one-scalar-generated $dS$ thick brane with a class of scalar-fermion couplings $η\barΨϕ^kΨ$ with positive odd integer $k$. A set of massive fermionic resonances for both chiralities are obtained when provided large couple constant $η$. We find that the masses and life-times of left and right chiral resonances are almost the same, which demonstrates that it is possible to compose massive Dirac fermions from the left and right chiral resonances. The resonance with lower mass has longer life-time. For a same set of parameters, the number of resonances increases with $k$ and the life-time of the lower level resonance for larger $k$ is much longer than the one for smaller $k$.

hep-th↗
arXiv2009

Bulk Matters on Symmetric and Asymmetric de Sitter Thick Branes

An asymmetric thick domain wall solution with de Sitter ($dS$) expansion in five dimensions can be constructed from a symmetric one by using a same scalar (kink) with different potentials. In this paper, by presenting the mass-independent potentials of Kaluza--Klein (KK) modes in the corresponding Schrödinger equations, we investigate the localization and mass spectra of various bulk matter fields on the symmetric and asymmetric $dS$ thick branes. It is shown that the spectrum of scalar KK modes on the symmetric $dS$ brane contains only one bound mode (the massless mode). However, for the asymmetric $dS$ brane with a large asymmetric factor $a$, there are two bound scalar KK modes: a zero mode and a massive mode. For spin 1 vectors, the spectra of KK modes on both $dS$ branes consist of a bound massless mode and a set of continuous ones, i.e., the asymmetric factor does not change the number of the bound vector KK modes. For spin 1/2 fermions with the scalar-fermion coupling $η\barΨ\sin(ϕ/ϕ_0)\cos^{-δ}(ϕ/ϕ_0)Ψ$, there exist some discrete bound KK modes and a series of continuous ones. The asymmetric factor $a$ reduces the number of the bound fermion KK modes.

hep-th↗
arXiv2007

The Energy-Level Shifts of a Stationary Hydrogen Atom in Static External Gravitational Field with Schwarzschild Geometry

The first order perturbations of the energy levels of a stationary hydrogen atom in static external gravitational field, with Schwarzschild metric, are investigated. The energy shifts are calculated for the relativistic 1S, 2S, 2P, 3S, 3P, 3D, 4S, 4P, 4D and 4F levels. The results show that the energy-level shifts of the states with total angular momentum quantum number 1/2 are all zero, and the ratio of absolute energy shifts with total angular momentum quantum number 5/2 is 1:4:5. This feature can be used to help us to distinguish the gravitational effect from other effect.

gr-qc↗
arXiv2007

The total energy-momentum of the universe in teleparallel gravity

We investigate the conservation law of energy-momentum in teleparallel gravity by using general Noether theorem. The energy-momentum current has also superpotential and is therefore identically conserved. The total energy-momentum, which includes the contributions of both matter and gravitational fields, is given by the integral of scalar densities over a three-dimensional spacelike hypersurface. As an example, the universe in teleparallel gravity is investigated. It is shown that the total energy-momentum vanishes independently of both the curvature parameter and the three dimensionless coupling constants of teleparallel gravity.

gr-qc↗
arXiv2007

Gravitational Corrections to the Energy-Levels of a Hydrogen Atom

The first order perturbations of the energy levels of a hydrogen atom in central internal gravitational field are investigated. The internal gravitational field is produced by the mass of the atomic nucleus. The energy shifts are calculated for the relativistic 1S, 2S, 2P, 3S, 3P, 3D, 4S and 4P levels with Schwarzschild metric. The calculated results show that the gravitational corrections are sensitive to the total angular momentum quantum number.

gr-qc↗