96 citations · 1.2k across the 37 of their papers we have counts for
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Invertible disformal transformations with higher derivatives
Kazufumi Takahashi, Hayato Motohashi, Masato Minamitsuji
We consider a higher-derivative generalization of disformal transformations in -dimensional spacetime and clarify the conditions under which they form a group with respect to th…
Nonlinear definition of the shadowy mode in higher-order scalar-tensor theories
Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi
We study U-DHOST theories, i.e., higher-order scalar-tensor theories which are degenerate only in the unitary gauge and yield an apparently unstable extra mode in a generic coordin…
Black hole perturbations in DHOST theories: Master variables, gradient instability, and strong coupling
Kazufumi Takahashi, Hayato Motohashi
We study linear perturbations about static and spherically symmetric black hole solutions with stealth scalar hair in degenerate higher-order scalar-tensor (DHOST) theories. We cla…