41793917
Quasinormal modes of boson stars.
We investigate nonradial oscillations of a boson star by taking into account the emission of the gravitational waves in the framework of general relativity. Since only even-parity modes of perturbations couple to the gravitational waves, we analyze these modes. We solve the linearized perturbed equations for l=2 modes and find that there exist new types of quasinormal modes of boson stars. Contrary to the behavior of quasinormal modes of compact fluid stars, the imaginary part of the frequencies of the normal modes of boson stars are large, which implies a short damping time scale of oscillations.
119398029
Highly damped quasinormal modes of Kerr black holes: A complete numerical investigation
We compute for the first time very highly damped quasinormal modes of the (rotating) Kerr black hole. Our numerical technique is based on a decoupling of the radial and angular equations, performed using a large-frequency expansion for the angular separation constant_{s}A_{l m}. This allows us to go much further in overtone number than ever before. We find that the real part of the quasinormal frequencies approaches a non-zero constant value which does not depend on the spin s of the perturbing field and on the angular index l: \omega_R=m\varpi(a). We numerically compute \varpi(a). Leading-order corrections to the asymptotic frequency are likely to be of order 1/\omega_I. The imaginary part grows without bound, the spacing between consecutive modes being a monotonic function of a.
31193559
Scalar perturbations of higher dimensional rotating and ultraspinning black holes
We investigate the stability of higher dimensional rotating black holes against scalar perturbations. In particular, we make a thorough numerical and analytical analysis of six dimensional black holes, not only in the low rotation regime but in the high rotation regime as well. Our results suggest that higher dimensional Kerr black holes are stable against scalar perturbations, even in the ultraspinning regime.
43796922
Classical instability of Kerr-AdS black holes and the issue of final state
It is now established that small Kerr\char21{}anti-de Sitter (Kerr-AdS) black holes are unstable against scalar perturbations, via the superradiant amplification mechanism. We show that small Kerr-AdS black holes are also unstable against gravitational perturbations and we compute the features of this instability. We also describe with great detail the evolution of this instability. In particular, we identify its end-point state. It corresponds to a Kerr-AdS black hole whose boundary is an Einstein universe rotating with the light velocity. This black hole is expected to be slightly oblate and to coexist in equilibrium with a certain amount of outside radiation.
119483126
Possible Measurement of Quintessence and Density Parameter Using Strong Gravitational Lensing Events
We propose a possible method of measurement of the time variability of the vacuum energy using strong gravitational lensing events. As an example we take an Einstein cross lens HST 14176+5226 and demonstrate that the measurement of the velocity dispersion with an accuracy of ± 5 km/sec may allow for the determination of the time dependence of the vacuum energy as well as the density parameter with an accuracy of order 0.1 if the lens model is fixed.
17445562
Accuracy of the relativistic Cowling approximation in slowly rotating stars
We have calculated the non-radial oscillation in slowly rotating relativistic stars with the Cowling approximation. The frequencies are compared with those based on the complete linearized equations of general relativity. It is found that the results with the approximation differ by less than about $20 %$ for typical relativistic stellar models. The approximation is more accurate for higher-order modes as in the Newtonian case.
138747704
Status of the MIR FEL Facility in Kyoto University
A mid-infrared free electron laser (MIR-FEL) facility (KU-FEL: Kyoto University Free Electron Laser) has been constructed for developing energy materials in Institute of Advanced Energy (IAE), Kyoto University. FEL gain saturation at 13.2 μm has been achieved for the first time in May 2008. A beam loading compensation method with feedforward RF phase control has been developed to supply the required quality of electron beam. The FEL beam characterization has been performed. The macro pulse energy of 5 mJ/pulse and the peak power of about 3 MW has been measured. The FEL transport system of wavelength range from 5 to 20 μm has been constructed to the application room. Applications of the MIR-FEL in the renewable energy research at Kyoto University will be started within this financial year.
8188983
Euclidean wormhole solutions of Einstein-Yang-Mills theory in diverse dimensions.
We solve the Euclidean Einstein equations with non-Abelian gauge fields of sufficiently large symmetry in various dimensions. In higher-dimensional spaces, we find the solutions which are similar to so-called scalar wormholes. In four-dimensional space-time, we find singular wormhole solutions with infinite Euclidean action. Wormhole solutions in the three-dimensional Einstein-Yang-Mills theory with a Chern-Simons term are also constructed.
54014117
END FIELD TERMINATION FOR BULK HTSC STAGGERED ARRAY UNDULATOR
Aiming at realizing a short period undulator with strong magnetic field, we have proposed a Bulk HTSC (High Temperature SuperConductor) Staggered Array Undulator which consists of Bulk HTSC magnets with a staggered array configuration [1]. The experiment with the prototype undulator at 77 K shows this configuration can be applicable to real device [2, 3]. We also estimated the magnetic performance of real devices by calculations with a loop current model based on Bean model of type II superconductor [4]. In these experiments, the magnetic field in the ends of the prototype were larger than the field in the center area. End field termination is required for practical use. To suppress the larger magnetic field for end field termination, we performed the calculations and the prototype experiments with the large end gap method. We concluded that the method is effective for Bulk HTSC Staggered Array Undulator.