61 citations · 221 across the 14 of their papers we have counts for
14 papers
Relation between circular photon orbits and the stability of wormholes with the thin shell of a barotropic fluid
Naoki Tsukamoto, Takafumi Kokubu
We cut a general, static, spherically symmetric spacetime and paste its copy to make a wormhole with a thin shell of any barotropic fluid in general relativity. We show that the st…
Quasi-periodic relativistic shells in reflecting boundaries: How likely are black holes to form?
Takafumi Kokubu
A system of two gravitating bodies floating around a restricted region of strong gravitational field is investigated. We consider two concentric spherically symmetric timelike shel…
Confined Penrose process with charged particles
Takafumi Kokubu, Shou-Long Li, Puxun Wu +1
We show that kinematics of charged particles allows us to model the growth of particles' energy by consecutive particle-splits, once a spherical mirror as a perfectly reflective bo…
High energy collision without fine tuning: Acceleration and multiple collisions of shells in a bound system
Takafumi Kokubu
High energy collision of massive bodies is investigated without fine tuning. We study multiple collisions of two spherical concentric shells in a gravitationally bound system and c…
Thin-shell wormholes in Einstein and Einstein-Gauss-Bonnet theories of gravity
Takafumi Kokubu, Tomohiro Harada
We review recent works on the possibility for eternal existence of thin-shell wormholes on Einstein and Einstein-Gauss-Bonnet gravity. We introduce thin-shell wormholes that are ca…
High energy particle collisions in static, spherically symmetric black-hole-like wormholes
Naoki Tsukamoto, Takafumi Kokubu
A Damour-Solodukhin wormhole with a metric which is similar to a Schwarzschild black hole seems to be a black hole mimicker since it is difficult to distinguish them by practical a…
Burst particle creation in gravitational collapse to a horizonless compact object
Takafumi Kokubu, Tomohiro Harada
In the previous paper [Harada, Cardoso, and Miyata, Phys.\ Rev.\ D {\bf 99} (2019), 044039], it is shown that a hollow transmissive shell collapsing to an ultracompact object of ra…
Particle creation in gravitational collapse to a horizonless compact object
Tomohiro Harada, Vitor Cardoso, Daiki Miyata
Black holes (BHs) play a central role in physics. However, gathering observational evidence for their existence is a notoriously difficult task. Current strategies to quantify the…
Effect of Inhomogeneity on Primordial Black Hole Formation in the Matter Dominated Era
Takafumi Kokubu, Koutarou Kyutoku, Kazunori Kohri +1
We investigate the effect of inhomogeneity on primordial black hole formation in the matter dominated era. In the gravitational collapse of an inhomogeneous density distribution, a…
Linear stability analysis of a rotating thin-shell wormhole
Naoki Tsukamoto, Takafumi Kokubu
We cut and paste two Banados-Teitelboim-Zanelli (BTZ) spacetimes at a throat by the Darmois-Israel method to construct a rotating wormhole with a thin shell filled with a barotropi…
Energy emission from high curvature region and its backreation
Takafumi Kokubu, Sanjay Jhingan, Tomohiro Harada
A strong gravity naked singular region can give important clues towards understanding classical as well as spontaneous nature of General Relativity. We propose here a model for ene…
Does the Gauss-Bonnet term stabilize wormholes?
Takafumi Kokubu, Hideki Maeda, Tomohiro Harada
The effect of the Gauss-Bonnet term on the existence and dynamical stability of thin-shell wormholes as negative tension branes is studied in the arbitrary dimensional spherically,…
Negative tension branes as stable thin shell wormholes
Takafumi Kokubu, Tomohiro Harada
We investigate negative tension branes as stable thin shell wormholes in Reissner-Nordstrom-(anti) de Sitter spacetimes in dimensional Einstein gravity. Imposing Z2 symmetry, w…
Escape of superheavy and highly energetic particles produced by particle collisions near maximally charged black holes
Hiroya Nemoto, Umpei Miyamoto, Tomohiro Harada +1
For particle collision near rapidly rotating Kerr black holes, the center-of-mass energy can be arbitrarily high if the angular momentum of either of the colliding particles is fin…