Kohkichi Konno

Rotating Black Hole in Extended Chern-Simons Modified Gravity

We investigate a slowly rotating black hole in four-dimensional extended Chern-Simons modified gravity. We obtain an approximate solution that reduces to the Kerr solution when a coupling constant vanishes. The Chern-Simons correction effectively reduces the frame-dragging effect around a black hole in comparison with that of the Kerr solution. Subject Index: 420, 453

General Relativistic Modification of a Pulsar Electromagnetic Field

We consider an exterior electromagnetic field surrounding a rotating star endowed with a dipole magnetic field in the context of general relativity. The analytic solution for a stationary configuration is obtained, and the general relativistic modifications and the implications for pulsar radiation are investigated in detail. We find that the general relativistic corrections of both the electric field strength and the curvature radii of magnetic field lines tend to enhance the curvature radiation photon energy.

Flat rotation curves in Chern-Simons modified gravity

Introduction.—There are three fundamental unsolved issues in the theory of gravity: quantization of gravity, dark energy, and dark matter. The string theory [1] is a promising candidate for a consistent quantum theory of gravity. Many attempts in quantizing gravity, however, have not been successful. In astronomy/astrophysics, a number of observations suggest the existence of dark energy [2, 3] and dark matter [3, 4]. Although many surveys of astrophysical objects have been conducted [5], it has not yet been revealed what is dark matter. For instance, the flat rotation curves of galaxies [6] have been considered to be a robust evidence of dark matter. The velocity v of a star orbiting around the center of a galaxy becomes a constant at a certain distance r far from the center. While the Newtonian gravity yields a relation v ∝ 1/ √ r. At present, we usually attribute the discrepancy to dark matter. However it may be still possible to explain the phenomenon based on a theory without dark matter. In this paper, we propose a model to solve this discrepancy in the framework of the Chern-Simons (CS) gravity.

High frequency response of p-i-n photodiodes analyzed by an analytical model in Fourier space

A formulation of carrier transport in vertical p-i-n photodiodes is presented in Fourier space, taking into account diffusion effects of carriers outside the intrinsic region. High frequency response of photodiodes is investigated using the model. Calculated results show that diffusion limits the cutoff frequency characteristics of photodiodes with short intrinsic region length. Photocurrent calculations via the spectral method are in excellent agreement with two-dimensional device simulator results. The model can be utilized in circuit simulation because of its reduced computational runtime.

Scalar field excited around a rapidly rotating black hole in Chern-Simons modified gravity

We discuss a Chern-Simons (CS) scalar field around a rapidly rotating black hole in dynamical CS modified gravity. The CS correction can be obtained perturbatively by considering the Kerr spacetime to be the background. We obtain the CS scalar field solution around the black hole analytically and numerically, assuming a stationary and axisymmetric configuration. The scalar field diverges on the inner horizon when we impose the boundary conditions that the scalar field be regular on the outer horizon and vanish at infinity. Therefore, the CS scalar field becomes problematic on the inner horizon.

Does a black hole rotate in Chern-Simons modified gravity?

The latest observational results of the cosmic microwave background (CMB) anisotropy from the Wilkinson Microwave Anisotropy Probe (WMAP) (1) are success- fully explained by thecold dark matter standard model. However, two big issues still remain: what is dark matter, and what is dark energy? According to the WMAP results, unfortunately about 96% of the contents of the Universe is given by the dark components that we still do not know. Therefore, properties of dark matter and dark energy have eagerly been investigated from observations (2,3). In contrast with the ordinary approaches (2,3), in which the existence of the dark components is assumed, it is of great interest to investigate alternative gravity theories (4 - 8) to solve the dark matter and dark energy problem. In this paper, we focus our attention on the Chern-Simons modi- fied gravity theory (9). This gravity theory was constructed by Deser et al. (9 )i n (2 � 1) spacetime dimensions for the first time by analogy with the topologically massive U(1) and SU(2) gauge theories. The Chern-Simons modified gravity theory was relatively recently extended by Jackiw and Pi (10 )t o (3 � 1) spacetime dimensions. In the ex- tended theory, the Schwarzschild solution holds without any modification (10). Therefore, the theory passes the classical tests of general relativity (11). In this gravity theory, however, the Kerr solution does not hold. Thus, the solution for a rotating black hole should have a differ- ent form from the Kerr solution. In � 2 � 1� -dimensional Chern-Simons modified gravity, a family of rotating black hole solutions was found by Moussa et al. (12). The solutions have a fascinating feature that observers in this spacetime behave like ones inside the ergosphere of the Kerr spacetime. This feature is similar to that of the rota- tion of galaxies (13). Therefore, it is very interesting to investigate rotating black hole solutions in the � 3 � 1� -dimensional Chern-Simons modified gravity theory. In this paper, we discuss rotating black hole solutions taking account of perturbation around the Schwarzschild solution. This paper is organized as follows. In Sec. II, we briefly review the � 3 � 1� -dimensional Chern-Simons modified gravity theory. In Sec. III, we consider the perturbation around the Schwarzschild solution to discuss slow rotation of the black hole. First we investigate a constraint equation independently of a choice of the embedding coordinate. In Sec. III A, from the first-order equations of the field equa- tion, we obtain the metric solution taking the embedding coordinate to be timelike. In Sec. III B, we investigate the metric solution for the case in which the embedding coor- dinate is spacelike. Finally, we provide a summary in Sec. IV. In this paper, we use a unit in which cG � 1.

Moments of inertia of relativistic magnetized stars

We consider principal moments of inertia of axisymmetric, magnetically deformed stars in the context of general relativity. The general expression for the moment of inertia with respect to the symmetric axis is obtained. The numerical estimates are derived for several polytropic stellar models. We find that the values of the principal moments of inertia are modified by a factor of 2 at most from Newtonian estimates.

Physics-Based Photodiode Model Enabling Consistent Opto-Electronic Circuit Simulation

The paper developed a photodiode (PD) model for circuit simulation considering, contrary to existing models, the transient carrier generation explicitly in the solution of the continuity equation. The developed model is compatible with conventional compact electrical device models and is demonstrated to enable accurate simulation of opto-electronic integrated circuits. The electric field distribution along the depth direction of the PD is found to cause a tail in the photo current, which has an adverse effect on optical response of PD and the performance of opto-electronic circuits. The developed opto-electronic circuit model is also applicable to predict how circuit performance is improved with respect to the improvement of photo diode characteristics

Limit of validity of the drift-diffusion approximation for simulation of photodiode characteristics

We have investigated the photoresponse of a Si p–n photodiode under different illumination and bias conditions. Under high illumination and low applied reverse bias, a clear discrepancy between experimental results and conventional two-dimensional device simulation results is observed. The discrepancy is found to be caused by the fact that the space-charge limitation effect under the drift-diffusion approximation used in conventional simulations does not describe the real situation. Thus, in the framework of the drift-diffusion approximation, modification of the mobility model is needed for the early stage of carrier transport under such operating conditions.

Parity violation in a single domain of spin-triplet Sr2RuO4 superconductors

Abstract We observed an unconventional parity-violating vortex in single domain Sr 2 RuO 4 single crystals using a transport measurement. The current–voltage characteristics of submicron Sr 2 RuO 4 show that the induced voltage has anomalous components which are even functions of the bias current. The results may suggest that the vortex itself has a helical internal structure characterized by a Hopf invariant (a topological invariant). We also discuss that the hydrodynamics of such a helical vortex causes the parity violation to retain the topological invariant.