Browsing by Author "Do, Tuan Q."

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Anisotropic power-law inflation for a conformal-violating Maxwell model
(2018-05-08)
Do, Tuan Q.
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Kao, W. F.
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物理研究所
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Institute of Physics
A set of power-law solutions of a conformal-violating Maxwell model with a non-standard scalar-vector coupling will be shown in this paper. In particular, we are interested in a coupling term of the form X(2n)F(mu v)F(mu v )with X denoting the kinetic term of the scalar field. Stability analysis indicates that the new set of anisotropic power-law solutions is unstable during the inflationary phase. The result is consistent with the cosmic no-hair conjecture. We show, however, that a set of stable slowly expanding solutions does exist for a small range of parameters lambda and n. Hence a small anisotropy can survive during the slowly expanding phase.
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
;
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.
Anisotropic power-law inflation for the Dirac-Born-Infeld theory
(2011-12-28)
Do, Tuan Q.
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Kao, W. F.
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物理研究所
;
Institute of Physics
We find a new set of the Bianchi type I power-law expanding solutions in a string-motivated Dirac-Born-Infeld theory. Stability analysis shows that these power-law inflationary solutions remain stable with or without the contribution of the Dirac-Born-Infeld effect. We also find a new set of Bianchi type I expanding power-law solutions in a two scalar Dirac-Born-Infeld model with an additional phantom field. It is shown that the inclusion of the phantom field turns the Bianchi type I power-law solutions unstable during the inflationary phase.
Anisotropic power-law inflation of the five dimensional scalar-vector and scalar-Kalb-Ramond model
(2018-06-28)
Do, Tuan Q.
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Kao, W. F.
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物理研究所
;
Institute of Physics
We will study the cosmological implications of the five dimensional scalar-vector and scalar-Kalb-Ramond model. In particular, a new set of Bianchi type I power-law analytic solution will be obtained for this model. The cosmic no-hair conjecture can be shown to break down in the presence of the scalar-vector and scalar-Kalb-Ramond couplings. The effect of the Kalb-Ramond field in the presence of the power-law solution will be shown explicitly. We will also show that the presence of a phantom field does, however, destabilize the corresponding Bianchi type I power-law inflationary solutions.
Anisotropic power-law solutions for a supersymmetry Dirac-Born-Infeld theory
(2016-04-21)
Do, Tuan Q.
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Kao, W. F.
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物理研究所
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Institute of Physics
A new set of Bianchi type I power-law expanding solutions is obtained for a supersymmetric Dirac-Born-Infeld (SDBI) theory coupled to a gauge field. Stability analysis is also performed to show that this set of power-law expanding solutions is stable. In particular, this set of power-law solutions provides an explicit example to the role played by the supersymmetry correction term. We also show by a general approach that any stable anisotropic solution of SDBI model will turn unstable when a phantom field is introduced. We also show that the result of the scalar perturbation indicates that the SDBI model is a realistic model.
Anisotropically expanding universe in massive gravity
(2013-09-05)
Do, Tuan Q.
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Kao, W. F.
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物理研究所
;
Institute of Physics
We study the cosmological implications of a ghost-free nonlinear massive gravity theory with a cosmological constant. We find that the massive terms serve as an effective cosmological constant for a large class of metric spaces with a compatible fiducial metric associated with the massive terms. A specific solution is solved as an example for this model under the Bianchi type I space and a compatible Bianchi type I fiducial metric. A stability analysis indicates that this set of solutions tends to be stable. Nonetheless, the anisotropically expanding solution will, in general, turn unstable when an additional scalar field with negative kinetic energy is introduced.
Bianchi type I anisotropic power-law solutions for the Galileon models
(2017-07-25)
Do, Tuan Q.
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Kao, W. F.
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物理研究所
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Institute of Physics
We will study the cosmological solutions of a class of Galileon models. A special class of the Bianchi type I power-law solutions will be presented in this paper. We will show that these Bianchi type I power-law solutions are stable during the inflationary phase. In addition, we will also show that the presence of a phantom field induces at least an unstable mode for the perturbation equation and destabilizes the power-law solutions.
Five-dimensional scalar-vector Kalb-Ramond black holes
(2020-02-10)
Do, Tuan Q.
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Kao, W. F.
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物理研究所
;
Institute of Physics
We will focus on a model with a scalar-vector coupling and a scalar Kalb-Ramond coupling. The Kalb-Ramond two-form is known to be equivalent to a U-1 gauge one-form in five dimensions. The model with both scalar-vector and scalar Kalb-Ramond interactions is hence effectively equivalent to an action with two independent vector fields. As a result, a new set of spherically symmetric black hole solutions will be presented for the scalar-vector Kalb-Ramond theory in five dimensions. We will show that the presence of the scalar fields and gauge fields affect the black hole structure in a nontrivial manner. Related implications will also be discussed in this paper.