Browsing by Author "Chang, ChiaMing"

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Stability analysis of the Lorentz Chern-Simons expanding solutions
(2011-09-26)
Chang, ChiaMing
;
Kao, W. F.
;
Lin, Ing-Chen
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物理研究所
;
Institute of Physics
A class of Bianchi type II expanding solutions in a Lorentz Chern-Simons theory has been known to break the cosmic no-hair theorem. These solutions do not approach the late-time de Sitter Universe. We will show that there are two independent solutions classified by the parameter p for each given cosmological constant Lambda. One of them is in the small-p phase; the other solution is in the large-p phase. It can be shown that an unstable mode always exists for the solution in its small-p phase that comes with smaller energy T-00 and T-00 + T/2. The result indicates that the large-p phase is unlikely to be stable from an observation of a modified version of Wald's theorem.
Weyl-invariant Kaluza-Klein theory and the teleparallel equivalent of Weyl-invariant general relativity
(2013-09-03)
Chang, ChiaMing
;
Kao, W. F.
;
物理研究所
;
Institute of Physics
A simple method is shown to demonstrate that the teleparallel equivalent of general relativity can be generalized to the Weyl-invariant models. We will also show explicitly that Weyl symmetry is preserved step by step throughout the 5D Kaluza-Klein dimensional-reduction process. As a result, the dimensional reduced model will be shown to be a theory with two scalar fields. When a symmetry-breaking potential is introduced, a strong constraint will effectively turn off one of the scalar fields. For heuristic reasons, the stability properties of the power-law solution associated with the resulting one-scalar-field model will be presented explicitly. In particular, all stable modes can be solved explicitly as functions of the free parameter associated with the symmetry-breaking potential.