Hang Bae Kim

It is suggested that an axino mass in the 10 MeV region and a gravitino mass in the sub-eV region can provide an explanation for the observed power spectrum. In this case, cold axions act as cold dark matter and axino decay products (gravitinos and axions) control the commencement of the matter domination.

In string or $M$ theory with a large compactification radius, some axionlike moduli can be much lighter than the gravitino. Generic moduli in gauge-mediated supersymmetry breaking models also have a mass far below the weak scale. Motivated by these, we examine the cosmological implications of light moduli for the mass range from the weak scale to an extremely small scale of $\mathcal{O}{(10}^{\ensuremath{-}26}) \mathrm{eV},$ and obtain an upper bound on the initial moduli misalignment for both c

The Telescope Array (TA) is a large scale ground experiment in Utah, USA for the measurement of extensive air showers from the ultra-high energy cosmic rays. Its construction is completed in March, 2008 and the data taking started. ?? 2009 The Physical Society of Japan.

Recent developments in string theory such as flux compactifications and moduli stabilization by non-perturbative effects of D-branes provided a solid framework where we discuss the realization of inflation in string theories. We review two prototype models, modular inflation and brane inflation, and discuss their observational consequences and outlook.

We study dynamics of rolling tachyon and Abelian gauge field on unstable D-branes, of which effective action is given by Born-Infeld type nonlocal action. Possible cosmological evolutions are also discussed. In the Einstein frame of string cosmology, every expanding flat universe is proven to be decelerating.

Cosmological implication of rolling tachyons is reported in the context of effective field theory. With a brief review of rolling tachyons in both flat and curved spacetimes, we study the string cosmological model with both tachyon and dilaton. In the string frame, flat space solutions of both initial-stage and late-time are obtained in closed form. In the Einstein frame, every expanding solution is decelerating. When a Born-Infeld U(1) gauge field is coupled, enhancement of e-folding of scale f

We analyze homogeneous anisotropic cosmology driven by the dilaton and the self-interacting ``massive'' antisymmetric tensor field which are indispensable bosonic degrees with the graviton in the NS-NS sector of string theories with $D$-branes. We found the attractor solutions for this system, which show the overall features of general solutions, and confirmed it through numerical analysis. The dilaton possesses the potential due to the presence of the $D$-brane and the curvature of extra dimens

Cosmological implication of rolling tachyons is reported in the context of effective field theory. With a brief review of rolling tachyons in both flat and curved spacetimes, we study the string cosmological model with both tachyon and dilaton. In the string frame, flat space solutions of both initial-stage and late-time are obtained in closed form. In the Einstein frame, every expanding solution is decelerating. When a Born-Infeld U(1) gauge field is coupled, enhancement of e-folding of scale f

We discuss the cosmological implications of an antisymmetric tensor .eld when it experiences a kind of \Higgs mechanism," including nonlocal interaction terms, on D-branes. Even when a huge magnetic-condensation-inducing anisotropy is assumed in the early universe, the expansion of the universe leads to an isotropic B-matter-dominated universe.

The void regions found in the arrival direction distribution of ultra-high-energy cosmic rays (UHECRs) observed by the Pierre Auger Observatory (PAO) may be an important clue in UHECR source hunting. We claim that there is a circular void band structure around the Centaurus A (Cen A) direction. We incorporated this observed void structure in the background contribution into the Cen A dominance model to improve the fitting of the arrival direction distribution. The best fit is obtained for the Ce

We obtain the static spherically symmetric vacuum solutions of Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity theory, imposing the detailed balance condition only in the UV limit. We find the solutions in two different coordinate systems, the Painlev\'e-Gullstrand coordinates and the Poincar\'e coordinates, to examine the consequences of imposing the projectability condition. The solutions in two coordinate systems are distinct due to the nonrelativistic nature of the Ho\ifmmode \check