Browsing by Author "Lin, Ing-Chen"

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Anisotropic power-law inflation for a two scalar fields model
(2011-06-07)
Do, Tuan Q.
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Kao, W. F.
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Lin, Ing-Chen
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物理研究所
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Institute of Physics
A special class of Bianchi type I expanding solutions in a string motivated theory with a single scalar field has been speculated to break the cosmic no-hair theorem that will not approach the late time isotropic expanding solution. We will show by a new perturbation approach that an unstable mode for the inflationary solutions exists when an additional phantom field is introduced. The result indicates that the existence of an unstable mode is closely related to the extra fields that could be present during the very early Universe.
Anisotropically inflating universes in a scalar-tensor theory
(2009-02-01)
Kao, W. F.
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Lin, Ing-Chen
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物理研究所
;
Institute of Physics
We show that a Brans-Dicke model admits some anisotropically inflating solutions which are identical to the solutions found in a higher derivative pure gravity theory. These inflating solutions were shown to break the cosmic no-hair theorem such that they do not approach the de Sitter universe at large times. The stability conditions of these solutions in this scalar-tensor theory are shown explicitly in this paper. It is shown that there exist unstable modes of the anisotropic perturbations. Therefore the inflating solutions are unstable in the scalar-tensor theory.
Bianchi type I expanding universe in Weyl-invariant gravity with a quartic interaction term
(2017-11-26)
Kao, W. F.
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Lin, Ing-Chen
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物理研究所
;
Institute of Physics
We will focus on the effect of a Weyl-invariant model with a quadratic interaction term and a free scalar field psi. A set of analytic solutions will be obtained for this model. This model provides a dynamical alternative to the standard Lambda CDM model. In particular, we will show that the quartic Weyl-invariant model prediction is consistent with the Hubble diagram observations.
Bianchi type I expanding universe in Weyl-invariant massive gravity
(2014-09-10)
Kao, W. F.
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Lin, Ing-Chen
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物理研究所
;
Institute of Physics
We will study the cosmological evolutions of aWeyl-invariant de Rham, Gabadadze, and Tolley (dRGT) massive gravity theory with a general fiducial metric. In the unitary gauge, this model is equivalent to a massive gauge field coupled to the dRGT massive gravity model. The massive gravity terms will serve as an effective cosmological constant for all metric spaces if the fiducial metric is treated as an auxiliary field. A further discussion will also be addressed on the bimetric theory. In particular, we will discuss the role played by the Weyl vector boson in Bianchi type I expanding space.
Stability analysis of the Lorentz Chern-Simons expanding solutions
(2011-09-26)
Chang, ChiaMing
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Kao, W. F.
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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.
Stability conditions for the Bianchi type II anisotropically inflating universes
(2009-01-01)
Kao, W. F.
;
Lin, Ing-Chen
;
物理研究所
;
Institute of Physics
Stability conditions for a class of anisotropically inflating solutions in the Bianchi type II background space are shown explicitly in this paper. These inflating solutions were known to break the cosmic no-hair theorem such that they do not approach the de Sitter universe at large times. It can be shown that unstable modes of the anisotropic perturbations always exist for this class of expanding solutions. As a result, we show that these set of anisotropically expanding solutions are unstable against anisotropic perturbations in the Bianchi type II space.
Stability of the anisotropically inflating Bianchi type VI expanding solutions
(2011-03-21)
Kao, W. F.
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Lin, Ing-Chen
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物理研究所
;
Institute of Physics
A special class of the Bianchi type VI expanding solutions was speculated to break the cosmic no-hair theorem that will not approach the late-time de Sitter solution. We will show that an unstable mode always exists when the perturbation of the field equations is applied to the system. In addition to a model-independent perturbation formula, a simplification is also achieved by the introduction of a delta R = 0 solution good for quadratic models in all Bianchi spaces. The result shows that this special class of anisotropically expanding solutions is unstable.