334 citations · 4k across the 75 of their papers we have counts for
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Differentiation identities for hypergeometric functions
Hayato Motohashi
It is well-known that differentiation of hypergeometric function multiplied by a certain power function yields another hypergeometric function with a different set of parameters. S…
Consistency of matter coupling in modified gravity
Kazufumi Takahashi, Rampei Kimura, Hayato Motohashi
Matter coupling in modified gravity theories is a nontrivial issue when the gravitational Lagrangian possesses a degeneracy structure to avoid the problem of the Ostrogradsky ghost…
Physical effects of gravitational waves: pedagogical examples
Hayato Motohashi, Teruaki Suyama
General relativity describes gravitation in terms of the geometry of spacetime. It predicts the existence of gravitational waves (GWs) that stretch and compress spacetime and were…
Generalized disformal Horndeski theories: cosmological perturbations and consistent matter coupling
Kazufumi Takahashi, Masato Minamitsuji, Hayato Motohashi
Invertible disformal transformations are a useful tool to investigate ghost-free scalar-tensor theories. By performing a higher-derivative generalization of the invertible disforma…
Spectroscopy of Kerr-AdS spacetime with the Heun function: Quasinormal modes, greybody factor, and evaporation
Sousuke Noda, Hayato Motohashi
We investigate quasinormal modes, greybody factor, and Hawking evaporation of a five-dimensional Kerr-anti de Sitter (AdS) black hole by solving a wave equation for a test mass…
Quasinormal modes of Schwarzschild black holes on the real axis
Koutarou Kyutoku, Hayato Motohashi, Takahiro Tanaka
We study the scattering of gravitational waves by a Schwarzschild black hole and its perturbed siblings to investigate influences of proposed spectral instability of quasinormal mo…
Evaporation of Echoing Black Holes
Naritaka Oshita, Hayato Motohashi, Sousuke Noda
We compute the graybody factor and evaporation rate of a rotating black hole in the presence of a hypothetical reflective surface slightly outside the outer horizon radius, assumin…
Black hole perturbations in higher-order scalar-tensor theories: initial value problem and dynamical stability
Keisuke Nakashi, Masashi Kimura, Hayato Motohashi +1
We propose a physically sensible formulation of initial value problem for black hole perturbations in higher-order scalar-tensor theories. As a first application, we study monopole…