Yoshiyuki Morisawa

Boundary value problem for five-dimensional stationary rotating black holes

We study the boundary value problem for stationary rotating black hole solutions to the five-dimensional vacuum Einstein equation. Assuming the existence of two additional commuting rotational Killing vector fields and sphericity of the horizon topology, we show that a black hole with a regular event horizon is uniquely characterized by its mass and a pair of angular momenta.

Kerr–Schild ansatz in Einstein–Gauss–Bonnet gravity: an exact vacuum solution in five dimensions

As is well known, Kerr-Schild metrics linearize the Einstein tensor. We shall see here that they also simplify the Gauss-Bonnet tensor, which turns out to be only quadratic in the arbitrary Kerr-Schild function f when the seed metric is maximally symmetric. This property allows us to give a simple analytical expression for its trace, when the seed metric is a five-dimensional maximally symmetric spacetime in spheroidal coordinates with arbitrary parameters a and b. We also write in a (fairly) simple form the full Einstein-Gauss-Bonnet tensor (with a cosmological term) when the seed metric is flat and the oblateness parameters are equal, a = b. Armed with these results we give in a compact form the solution of the trace of the Einstein-Gauss-Bonnet field equations with a cosmological term and a ≠ b. We then examine whether this solution for the trace does solve the remaining field equations. We find that it does not in general, unless the Gauss-Bonnet coupling is such that the field equations have a unique maximally symmetric solution.

Vacuum solutions of five dimensional Einstein equations generated by inverse scattering method

We study stationary and axially symmetric two solitonic solutions of five dimensional vacuum Einstein equations by using the inverse scattering method developed by Belinski and Zakharov. In this generation of the solutions, we use five dimensional Minkowski spacetime as a seed. It is shown that if we restrict ourselves to the case of one angular momentum component, the generated solution coincides with a black ring solution with a rotating two sphere which was found by Mishima and Iguchi recently.

Scalar perturbation of the higher-dimensional rotating black holes

The massless scalar field in the higher-dimensional Kerr black hole (Myers- Perry solution with a single rotation axis) has been investigated. It has been shown that the field equation is separable in arbitrary dimensions. The quasi-normal modes of the scalar field have been searched in five dimensions using the continued fraction method. The numerical result shows the evidence for the stability of the scalar perturbation of the five-dimensional Kerr black holes. The time scale of the resonant oscillation in the rapidly rotating black hole, in which case the horizon radius becomes small, is characterized by (black hole mass)^{1/2}(Planck mass)^{-3/2} rather than the light-crossing time of the horizon.

Relativistic Gravitational Collapse of a Cylindrical Shell of Dust. II— Settling Down Boundary Condition —

We numerically study the dynamics of an imploding hollow cylinder composed of dust. Since there is no cylindrical black hole in 4-dimensional spacetime with physically reasonable energy conditions, a collapsed dust cylinder involves a naked singularity accompanied by its causal future, or a fatal singularity which terminates the history of the whole universe. In a previous paper, the present authors have shown that if the dust is assumed to be composed of collisionless particles such that these particles go through the symmetry axis of the cylinder, then the scalar polynomial singularity formed on the symmetry axis is so weak that almost all of geodesics are complete, and thus effectively no singularity forms by the collapse of a hollow dust cylinder. By contrast, in this paper, we assume that whole of the collapsed dust settles down on the symmetry axis by changing its equation of state. Obtained solutions are the straightforward extension of Morgans null dust solution, in which no gravitational radiation is emitted. However, in the present case with timelike dust, infinite amount of

Mass and angular momenta of Kerr anti-de Sitter spacetimes in Einstein-Gauss-Bonnet theory

C

Charged rotating Kaluza–Klein black holes generated by G2(2) transformation

-energy initially stored in the system is released through gravitational radiation. We also show that the gravitational waves asymptotically behave in a self-similar manner.

High-Speed Cylindrical Collapse of Perfect Fluid

We briefly review how to compute the mass and angular momenta of rotating, asymptotically anti-de Sitter spacetimes in Einstein-Gauss-Bonnet theory of gravity using superpotentials derived from standard Noether identities. The calculations depend on the asymptotic form of the metrics only and hence take no account of the source of the curvature. When the source of curvature is a black hole, the results can be checked using the first law of black hole thermodynamics.

Thick domain walls intersecting a black hole

Applying the G2(2) generating technique for minimal D = 5 supergravity to the Rasheed black hole solution, we present a new rotating charged Kaluza–Klein black hole solution to the five-dimensional Einstein–Maxwell–Chern–Simons equations. At infinity, our solution behaves as a four-dimensional flat spacetime with a compact extra dimension and hence describes a Kaluza–Klein black hole. In particular, the extreme solution is non-supersymmetric, which is in contrast to a static case. Our solution has the limits to the asymptotically flat charged rotating black hole solution and a new charged rotating black string solution.

Cosmological black holes on taub-NUT space in five-dimensional Einstein-Maxwell theory

The gravitational collapse of a cylindrically distributed perfect fluid is studied. We assume that the collapsing speed of the fluid is very large and investigate such a situation using recently proposed high-speed approximation scheme. We show that if the value of the pressure divided by the energy density is bounded below by some positive value, the high-speed collapse is necessarily decelerated by pressure repulsion so significantly that this approximation scheme becomes inapplicable. However, even in the case of a mono-atomic ideal gas, which is a typical example of the bounded case, an arbitrarily large tidal force for freely falling observers can be realized before the high-speed approximation breaks down if the initial collapsing velocity is set to a very large value. By contrast, in case that the equation of state is sufficiently soft, we find that the high-speed collapse is maintained until a spacetime singularity forms.