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Zhe Chang

Publications and source records attributed to Zhe Chang.

At least 127 records · Page 7Linked to original sources
arXiv2008

Lorentz Invariance Violation and Symmetry in Randers--Finsler Spaces

Lorentz Invariance violation is a common feature of new physics beyond the standard model. We show that the symmetry of Randers spaces deduces a modified dispersion relation with characteristics of Lorentz Invariance violation. The counterparts of the Lorentz transformation in the Einstein's Special Relativity are presented explicitly. The coordinate transformations are unitary and form a group. Generators and algebra satisfied by them are different from usual Lorentz ones. The Randersian line element as well as speed of light is invariant under the transformations. In particular, there is another invariant speed which may be related with Planck scale and the mass of moving particle. Thus, the Randers spaces is a suitable framework to discuss the Lorentz Invariance violation.

hep-th↗
arXiv2008

Gravitational collapse of a spherical star with heat flow as a possible energy mechanism of gamma-ray bursts

We investigate the gravitational collapse of a spherically symmetric, inhomogeneous star, which is described by a perfect fluid with heat flow and satisfies the equation of state $p=ρ/3$ at its center. In the process of the gravitational collapsing, the energy of the whole star is emitted into space. And the remaining spacetime is a Minkowski one without a remnant at the end of the process. For a star with a solar mass and solar radius, the total energy emitted is at the order of $10^{54}$ {\rm erg}, and the time-scale of the process is about $8s$. These are in the typical values for a gamma-ray burst. Thus, we suggest the gravitational collapse of a spherical star with heat flow as a possible energy mechanism of gamma-ray bursts.

gr-qc↗
arXiv2008

Ashkin-Teller formalism for elastic response of DNA molecule to external force and torque

We propose an Ashkin-Teller like model for elastic response of DNA molecule to external force and torque. The base-stacking interaction is described in a simple and uniform way. We obtain the phase diagram of dsDNA, and in particular, the transition from B form to the S state induced by stretching and twisting. The elastic response of the ssDNA is presented also in a unified formalism. The close relation of dsDNA molecule structure with elastic response is shown clearly. The calculated folding angle of the dsDNA molecule is $59.2^o$.

physics.bio-ph↗
arXiv2008

Topology Changes and Quantum Phase Transition in Spin-Chain System

The standard Landau-Ginzburg scenario of phase transition is broken down for quantum phase transition. It is difficult to find an order parameter to indicate different phases for quantum fluctuations. Here, we suggest a topological description of the quantum phase transition for the XY model. The ground states are identified as a specialized U(1) principal bundle on the base manifold $S^2$. And then different first Chern numbers of U(1) principal bundle on the base manifold $S^2$ are associated to each phase of quantum fluctuations. The particle-hole picture is used to parameterized the ground states of the XY system. We show that a singularity of the Chern number of the ground states occurs simultaneously with a quantum phase transition. The Chern number is a suitable topological order of the quantum phase transition.

quant-ph↗
arXiv2007

Toward a Gravitation Theory in Berwald--Finsler Space

Finsler geometry is a natural and fundamental generalization of Riemann geometry. The Finsler structure depends on both coordinates and velocities. It is defined as a function on tangent bundle of a manifold. We use the Bianchi identities satisfied by Chern curvature to set up a gravitation theory in Berwald-Finsler space. The geometric part of the gravitational field equation is nonsymmetric in general. This indicates that the local Lorentz invariance is violated. Nontrivial solutions of the gravitational field equation are presented.

gr-qc↗
arXiv2005

Constraints on holographic dark energy from X-ray gas mass fraction of galaxy clusters

We use the Chandra measurements of the X-ray gas mass fraction of 26 rich clusters released by Allen et al. to perform constraints on the holographic dark energy model. The constraints are consistent with those from other cosmological tests, especially with the results of a joint analysis of supernovae, cosmic microwave background, and large scale structure data. From this test, the holographic dark energy also tends to behave as a quintom-type dark energy.

astro-ph↗
arXiv2005

Cosmic ray threshold in an asymptotically dS spacetime

We discuss the threshold anomaly in ultra-high energy cosmic ray physics by assuming that the matter world just be perturbation of a de Sitter universe, which is consistent with the recent astronomical observations: about two thirds of the whole energy in the universe is contributed by a small positive cosmological constant. One-particle states are presented explicitly. It is noticed that the dispersion relation of free particles is dependent on the degrees of freedom of angular momentum. This fact can be regarded as the effects of the cosmological constant on kinematics of particles.

astro-ph↗
arXiv2004

Vacuum Energy Density and Cosmological Constant in dS Brane World

We discuss the vacuum energy density and the cosmological constant of dS$_5$ brane world with a dilaton field. It is shown that a stable AdS$_4$ brane can be constructed and gravity localization can be realized. An explicit relation between the dS bulk cosmological constant and the brane cosmological constant is obtained. The discrete mass spectrum of the massive scalar field in the AdS$_4$ brane is used to acquire the relationship between the brane cosmological constant and the vacuum energy density. The vacuum energy density in the brane gotten by this method is in agreement with astronomical observations.

hep-th↗
arXiv2004

Statistical properties of radiation fields in a compact space

We discuss radiation fields in a compact space of finite size instead of that in a cavity for investigating the coupled atom-radiation field system. Representations of $T(1)\times SO(4)$ group are used to give a formulation for kinematics of the radiation fields. The explicit geometrical parameter dependence of statistical properties of radiation fields is obtained. Results show remarkable differences from that of the black-body radiation system in free space.

quant-ph↗
arXiv2004

Effects of the Cosmological Constant as the Origin of the Cosmic-Ray Paradox

We show that a tiny but non-zero positive cosmological constant, which has been strongly suggested by the recent astronomical observations on supernovae and CMBR, may change notably the behaviors of the ultrahigh energy cosmic ray interacting with soft photons. The threshold anomaly of the ultrahigh energy cosmic ray disappears naturally after the effects of the cosmological constant are taken into account.

astro-ph↗
arXiv2004

Cosmic ray threshold anomaly and kinematics in the dS spacetime

We present a covariant framework of kinematics in the dS spacetime, which is a natural postulate of recent astronomical observations ($Λ>0)$. One-particle states are presented explicitly. It is noticed that the dispersion relation of free particles is dependent on the degrees of freedom of angular momentum and spin. This fact can be referred to as the effects of the cosmological constant on kinematics of particles. The kinematics in dS spacetime is used to investigate the phenomenon of ultra high energy cosmic rays. We emphasize the possibility of solving the threshold anomalies of the interactions between ultra high energy cosmic rays and soft photons in the covariant framework of kinematics in the dS spacetime.

astro-ph↗
arXiv2003

Minkowski Brane in Asymptotic dS$_5$ Spacetime without Fine-tuning

We discuss properties of a 3-brane in an asymptotic 5-dimensional de-Sitter spacetime. It is found that a Minkowski solution can be obtained without fine-tuning. In the model, the tiny observed positive cosmological constant is interpreted as a curvature of 5-dimensional manifold, but the Minkowski spacetime, where we live, is a natural 3-brane perpendicular to the fifth coordinate axis.

hep-th↗
arXiv2002

Thermodynamics of a deformed Bose gas

By making use of the double-time Green function technique, we study thermodynamics of a deformed Bose gas, which describes well properties of density intensive photonic gas and radiation fields of the early universe. General form of statistical distribution function is obtained. We show explicitly the expression of the distribution function in some limitation cases. The free energy, equation of state, specific heat and other thermodynamic properties of the deformed Bose gas are presented.

cond-mat↗
arXiv2002

Possible Effects of Noncommutative Geometry on Weak CP Violation and Unitarity Triangles

Possible effects of noncommutative geometry on weak CP violation and unitarity triangles are discussed by taking account of a simple version of the momentum-dependent quark mixing matrix in the noncommutative standard model. In particular, we calculate nine rephasing invariants of CP violation and illustrate the noncommutative CP-violating effect in a couple of charged D-meson decays. We also show how inner angles of the deformed unitarity triangles are related to CP-violating asymmetries in some typical B_d and B_s transitions into CP eigenstates. B-meson factories are expected to help probe or constrain noncommutative geometry at low energies in the near future.

hep-ph↗
arXiv2000

Global geometric properties of AdS space and the AdS/CFT correspondence

The Poisson kernels and relations between them for a massive scalar field in a unit ball $B^n$ with Hua's metric and conformal flat metric are obtained by describing the $B^n$ as a submanifold of an $(n+1)$-dimensional embedding space. Global geometric properties of the AdS space are discussed. We show that the $(n+1)$-dimensional AdS space AdS$_{n+1}$ is isomorphic to $RP^1\times B^n$ and boundary of the AdS is isomorphic to $RP^1\times S^{n-1}$. Bulk-boundary propagator and the AdS/CFT like correspondence are demonstrated based on these global geometric properties of the $RP^1\times B^n$.

hep-th↗
arXiv1999

Symmetry Realization, Poisson Kernel and the AdS/CFT Correspondence

Two kinds of realizations of symmetry on classical domains or the Euclidean version of AdS space are used to study AdS/CFT correspondence. Mass of free particles is defined as an AdS group invariant, the Klein-Gordon and Dirac equations for relativistic particles in the AdS space are set up as a mimic in the case of Minkowskian space. The bulk-boundary propagator on the AdS space is given by the Poisson kernel. Theorems on the Poisson kernel guarantee the existence and sole of the bulk-boundary propagator. The propagator is used to calculate correlators of the theories that live on the boundary of the AdS space and show conformal invariance, which is desired by the AdS/CFT correspondence.

hep-th↗
arXiv1999

Holography based on noncommutative geometry and the AdS/CFT correspondence

Exponential regularization of orthogonal and Anti-de Sitter (AdS) space is presented based on noncommutative geometry. We show that an adequately adopted noncommutative deformation of geometry makes the holography of higher dimensional quantum theory of gravity and low dimensional theory possible. Detail counting for observable degrees of freedom of quantum system of gravity in the bulk of noncommutative space SO_q(3) and the classical limit of its boundary surface S^2 is discussed. Taking noncommutivity effect into account, we get the desired form of entropy for our world, which is consistent with the physical phenomena associated with gravitational collapse. Conformally invariant symmetry is obtained for the equivalent theory of the qunatum gravity living on the classical limit of boundary of the noncommutative AdS space. This is the basis of the AdS/CFT correspondence in string theory.

hep-th↗