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Is dark energy the only solution to the apparent acceleration of the present universe?
Hideo Iguchi, Takashi Nakamura, Ken-ichi Nakao
Even for the observed luminosity distance D_L(z), which suggests the existence of dark energy, we show that an inhomogeneous dust universe solution without dark energy is possible…
Oscillating scalar-field dark matter in supergravity
Osamu Seto, K. Kohri, Takashi Nakamura
We show that an oscillating scalar field in supergravity of mass of the order of TeV with a nonzero vacuum expectation value ( GeV) can be a candidate of cold…
Peak Luminosity-Spectral Lag Relation Caused by the Viewing Angle of the Collimated Gamma-Ray Bursts
Kunihito Ioka, Takashi Nakamura
We compute the kinematical dependence of the peak luminosity, the pulse width and the spectral lag of the peak luminosity on the viewing angle of a jet. For appropriate model…
Microlensing of collimated Gamma-Ray Burst afterglows
Kunihito Ioka, Takashi Nakamura
We investigate stellar microlensing of the collimated gamma-ray burst afterglows. A spherical afterglow appears on the sky as a superluminally expanding thin ring (``ring-like'' im…