28 citations · 136 across the 11 of their papers we have counts for
12 papers
Ellis-Bronnikov wormholes with NUT charge
Masato Nozawa, Tomohiro Harada, Keisuke Nakashi
We construct an exact NUT-charged generalization of the Ellis-Bronnikov wormhole in the Einstein-phantom-scalar system. The solution is stationary, asymptotically locally flat at b…
Ellis-Bronnikov Wormhole Shadows with Spherically Symmetric Accretion Flow
Mikiya M. Takahashi, Keisuke Nakashi
We investigate the observational differences between the Ellis--Bronnikov (EB) wormhole and the Schwarzschild black hole (BH) by performing general relativistic radiative transfer…
Probing higher curvature gravity via ringdown with overtones
Keisuke Nakashi, Masashi Kimura, Hayato Motohashi +1
We investigate metric perturbations of a spherically symmetric black hole in higher curvature gravity. We show that higher curvature corrections deform the near-horizon region of t…
Black hole ringdown from physically sensible initial value problem in higher-order scalar-tensor theories
Keisuke Nakashi, Masashi Kimura, Hayato Motohashi +1
We study odd-parity perturbations about static and spherically symmetric black hole solutions with a linearly time-dependent scalar field in higher-order scalar-tensor theories. In…
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…
Revisiting timelike geodesics in the Fisher-Janis-Newman-Winicour-Wyman spacetime
Keisuke Ota, Shinpei Kobayashi, Keisuke Nakashi
We investigate the timelike geodesics and the periapsis precession of orbits in the Fisher-Janis-Newman-Winicour-Wyman spacetime. This spacetime represents the naked singularity sp…
Photon surfaces in less symmetric spacetimes
Yasutaka Koga, Takahisa Igata, Keisuke Nakashi
We investigate photon surfaces and their stability in a less symmetric spacetime, a general static warped product with a warping function acting on a Riemannian submanifold of codi…
Towards rotating non-circular black holes in string-inspired gravity
Keisuke Nakashi, Masashi Kimura
We study stationary slowly rotating black holes, up to quadratic order in the spin angular momentum, in dynamical Chern-Simons gravity and shift symmetric Einstein scalar Gauss-Bon…
Observability of the innermost stable circular orbit in a near-extremal Kerr black hole
Takahisa Igata, Keisuke Nakashi, Kota Ogasawara
We consider the escape probability of a photon emitted from the innermost stable circular orbit (ISCO) of a rapidly rotating black hole. As an isotropically emitting light source o…
Effect of a second compact object on stable circular orbits
Keisuke Nakashi, Takahisa Igata
We investigate how stable circular orbits around a main compact object appear depending on the presence of a second one by using the Majumudar--Papapetrou dihole spacetime, which c…
Innermost stable circular orbits in Majumdar--Papapetrou dihole spacetime
Keisuke Nakashi, Takahisa Igata
We investigate the positions of stable circular massive particle orbits in the Majumdar--Papapetrou dihole spacetime with equal mass. In terms of qualitative differences of their s…
Null Geodesics and Repulsive Behavior of Gravity in (2+1)-dimensional Massive Gravity
Keisuke Nakashi, Shinpei Kobayashi, Shu Ueda +1
We study the null geodesics in a static circularly symmetric (SCS) black hole spacetime which is a solution in the -dimensional massive gravity proposed by Bergshoeff, Hohm…