96 citations · 1.2k across the 37 of their papers we have counts for
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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…
Approximately stealth black hole in higher-order scalar-tensor theories
Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi
We investigate a generic quadratic higher-order scalar-tensor theory with a scordatura term, which is expected to provide a consistent perturbative description of stealth solutions…
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…
Generalized Regge-Wheeler Equation from Effective Field Theory of Black Hole Perturbations with a Timelike Scalar Profile
Shinji Mukohyama, Kazufumi Takahashi, Vicharit Yingcharoenrat
Recently, the Effective Field Theory (EFT) of perturbations on an arbitrary background metric with a timelike scalar profile was formulated in the context of scalar-tensor theories…
Linear stability of black holes with static scalar hair in full Horndeski theories: generic instabilities and surviving models
Masato Minamitsuji, Kazufumi Takahashi, Shinji Tsujikawa
In full Horndeski theories, we show that the static and spherically symmetric black hole (BH) solutions with a static scalar field~ whose kinetic term~ is nonvanishing on the…
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…
Built-in scordatura in U-DHOST
Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi
Modified gravity theories can accommodate exact solutions, for which the metric has the same form as the one in general relativity, i.e., stealth solutions. One problem with these…
Linear stability of black holes in shift-symmetric Horndeski theories with a time-independent scalar field
Masato Minamitsuji, Kazufumi Takahashi, Shinji Tsujikawa
We study linear perturbations about static and spherically symmetric black holes with a time-independent background scalar field in shift-symmetric Horndeski theories, whose Lagran…