214 citations · 1.6k across the 81 of their papers we have counts for
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Expanding universe with nonlinear gravitational waves
Taishi Ikeda, Chul-Moon Yoo, Yasusada Nambu
We test the validity of Isaacson's formula which states that high frequency and low amplitude gravitational waves behave as a radiation fluid on average. For this purpose, we numer…
Derivation of Markovian master equation by renormalization group method
Yasusada Nambu, Shingo Kukita
We present a derivation of the Markovian master equation by the renormalization group method. Starting from a naive perturbative solution of the von Neumann equation, the reduced d…
Spherical polytropic balls cannot mimic black holes
Hiromi Saida, Atsuhito Fujisawa, Chul-Moon Yoo +1
The so-called black hole shadow is a dark region which is expected to appear in a fine image of optical observation of black holes. It is essentially an absorption cross section of…
Maximum mass of a barotropic spherical star
Atsuhito Fujisawa, Hiromi Saida, Chul-Moon Yoo +1
The ratio of total mass to surface radius of spherical perfect fluid ball has an upper bound, . Buchdahl obtained under the assumptions; non-increasing m…
Wave Optics in Black Hole Spacetimes: Schwarzschild Case
Yasusada Nambu, Sousuke Noda
We investigate the wave optics in the Schwarzschild spacetime. Applying the standard formalism of wave scattering problems, the Green function represented by the sum over the parti…