334 citations · 4k across the 75 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…
Inflation with
Mohammad Ali Gorji, Hayato Motohashi, Shinji Mukohyama
We investigate a novel single field inflationary scenario which allows a transition between a slow-roll k-inflation with of order unity and a ghost inflation with $ c_{…
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…
Exact solution for wave scattering from black holes: Formulation
Hayato Motohashi, Sousuke Noda
We establish an exact formulation for wave scattering of a massless field with spin and charge by a Kerr-Newman-de Sitter black hole. Our formulation is based on the exact solution…