arXiv subjects

G. Y. Chee

Publications and source records attributed to G. Y. Chee.

8 recordsLinked to original sources

arXiv2024

Lorentz group in gravity theories

In this paper, it is argued that in gravity theories the local Lorentz group can not be considered as a gauge group in the sense of Yang-Mills theories, the Lorentz connection is not a gauge potential but an artificial force, the inertial force. A genuine gravity theory should be a translation gauge theory, though a unnormal gauge theory. All the three theories of the Geometrical Trinity of Gravity are translation gauge theories. A real gravity theory should get rid of "gauging" Lorentz group. The covariantization of the teleparallel gravity is not necessary physically.

gr-qc↗

arXiv2016

A Poincare-Starobinsky-Yang-Mills type model of dark energy

Starting from the Poincare Gauge principle and a Starobinsky-Yang-Mills type Lagrangian a model of dark energy is developed. In order to evade any unnecessary controversy regarding frames (i.e. Einstein .vs. Jordan) the theory is treated using the original variables instead of transforming them to a scalar-tensor theory. The field equations are derived directly from the original Lagrangian using the variational principle. The cosmological equations are different from the Friedmann equations, but the acceleration equation gives the same result as the one of the $Λ$CDM model in the matter-dominated era. Furthermore, it indicates an inflation in the early time and the radiation-dominated era as the Starobinsky model. The cosmological constant naturally emerges from the Yang-Mills terms of the Lagrangian rather than be added artificially. The equation of state of the dark energy depends on the density of the matter and then the coincidence and fine tuning problem is solved naturally. In order to compare with the popular $Λ$CDM model, the cosmological perturbations is investigated. The equations for linear perturbations of the metric and for the density contrast growth are derived. The explicit analytic solutions are obtained. The gravitational potential and the growth of the baryon matter density perturbation can be used to clarify whether this model is in agreement with standard $Λ$CDM predictions and experimental data.

gr-qc↗

arXiv2013

Acceleration of the cosmic expansion induced by symmetry breaking

It is proved that in order to obtain a model of the accelerated cosmic expansion the thing one only need to do is to add a perturbation term to the Einstein-Hilbert Lagrangian. This term leads to some symmetry breaking terms in the fields equation, which makes the cosmic expansion accelerating. A vacuum de Sitter solution is obtained. A new explanation of the acceleration of the cosmic expansion is presented. In this model the changing of the expansion from decelerating to accelerating is an intrinsic property of the universe without need of an exotic dark energy. The acceleration of the cosmic expansion is induced by the symmetry breaking perturbation of the gravitational energy. The cosmological constant problem, the coincidence problem and the problem of phantom divide line crossing are naturally solved. The results of the model are roughly consistent with the observations.

gr-qc↗

arXiv2013

Cosmic acceleration and the change of the Hubble parameter

A new model of accelerating expansion of the universe is presented. A de Sitter solution in vacuum and a exact solution with the dust mater source are obtained. A new explanation of the acceleration of the cosmic expansion is given. In is proved that the changing of the expansion from decelerating to accelerating is an intrinsic property of the universe without need of dark energy.

physics.gen-ph↗

arXiv2005

Boundary term, extended Witten identities and positivity of energy

In terms of two-spinors a chiral formulation of general relativity with the Ashtekar Lagrangian and its Hamiltonian formalism in which the basic dynamic variables are the dyad spinors are presented. The extended Witten identities are derived. A new expression of the Hamiltonian boundary term is obtained. Using this expression and the extended Witten identities the proof of the positive energy theorem is extended to a case including momentum and angular momentum.

gr-qc↗

arXiv2004

Self-dual teleparallel gravity and the positive energy theorem

A self-dual and anti-self-dual decomposition of the teleparallel gravity is carried out and the self-dual Lagrangian of the teleparallel gravity which is equivalent to the Ashtekar Lagrangian in vacuum is obtained. Its Hamiltonian formulation and the constraint analysis are developed. Starting from Witten's equation Nester's gauge condition is derived directly and a new expression of the boundary term is obtained. Using this expression and Witten's identity the proof of the positive energy theorem by Nester et al is extended to a case including momentum.

gr-qc↗

arXiv2004

Symmetric Hyperbolic System in the Self-dual Teleparallel Gravity

In order to discuss the well-posed initial value formulation of the teleparallel gravity and apply it to numerical relativity a symmetric hyperbolic system in the self-dual teleparallel gravity which is equivalent to the Ashtekar formulation is posed. This system is different from the ones in other works by that the reality condition of the spatial metric is included in the symmetric hyperbolicity and then is no longer an independent condition. In addition the constraint equations of this system are rather simpler than the ones in other works.

gr-qc↗

arXiv2001

Gravitational energy-momentum and the Hamiltonian formulation of the teleparallel gravity

The transformation properties of the gravitational energy-momentum in the teleparallel gravity are analyzed. It is proved that the gravitational energy-momentum in the teleparallel gravity can be expressed in terms of the Lorentz gauge potential, and therefore is not covariant under local Lorentz transformations. On the other hand, it can also be expressed in terms of the translation gauge field strength, and therefore is covariant under general coordinate transformations. A simplified Hamiltonian formulation of the teleparallel gravity is given. Its constraint algebra has the same structure as that of general relativity, which indicates the equivalence between the teleparallel gravity and general relativity in the Hamiltonian formulation.

gr-qc↗