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Cosmological Aspects of the D-brane world
Inyong Cho,김항배,Eung Jin Chun,Yoonbai Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I
The D-brane world is the idea that we are living on the D-brane imbedded in a 10- or 11- dimensional spacetime of string theory, aiming at the construction of realistic models from string theory. We investigate the cosmological aspects of the D-brane world, focusing on homogeneous anisotropic cosmology driven by the dilaton and the NS-NS 2-form field which becomes massive in the presence of the D-brane. The dilaton possesses the potential due to the presence of the Dbrane, various form field fluxes, and the curvature of extra dimensions. In the absence of stabilizing potential, we found the attractor solutions for this system which show the overall features of general solutions. In the presence of non-vanishing NS-NS 2-form field, the homogeneous universe expands anisotropically while the D-brane term dominates. Isotropy is recovered as the dilaton rolls down and the curvature term dominates. With the stabilizing potential for the dilaton, the anisotropy developed by the initial NS-NS 2-form field flux is erased as the NS-NS 2-form field begins to oscillate around the minimum, forming B-matter, and an isotropic matter-dominated universe is obtained.
Numerical study of instability of fluid black holes
Cho Inyong,Park Dong-Ho 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.10
Recently neutral and charged black-hole solutions were found for static perfect fluid with the equation of state p(r) = −ρ(r)∕3 , for fluid only as well as for fluid in the presence of electric field. In those works, the stability of the black holes were studied in an analytic manner, which concluded that the black holes are unconditionally unstable. In this work, we focus particularly on the numerical study of the instability. For the black-hole solutions as well as the static solutions without horizons, we solve the perturbation equations numerically and find the unstable mode functions.
Cho, Inyong,Kim, Hyeong-Chan American Physical Society 2017 Physical Review D Vol.95 No.8
<P>We investigate black holes formed by static perfect fluid with p = -rho/3. These represent the black holes in S-3 and H-3 spatial geometries. There are three classes of black-hole solutions, two S-3 types and one H-3 type. The interesting solution is the S-3 type one, which possesses two singularities. One is at the north pole behind the horizon, and the other is naked at the south pole. The observers, however, are free from falling to the naked singularity. There are also nonstatic cosmological solutions in S-3 and H-3 and a singular static solution in H-3.</P>