Waseda University

About: Waseda University is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Large Hadron Collider & Catalysis. The organization has 24220 authors who have published 46859 publications receiving 837855 citations. The organization is also known as: Waseda daigaku & Sōdai.

Classical instability of Kerr-AdS black holes and the issue of final state

Abstract: It is now established that small Kerr--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.

Combined search for the Standard Model Higgs boson in pp collisions at root s=7 TeV with the ATLAS detector

Abstract: A combined search for the Standard Model Higgs boson with the ATLAS detector at the LHC is presented. The data sets used correspond to integrated luminosities from 4.6 fb(-1) to 4.9 fb(-1) of proton-proton collisions collected at root s = 7 TeV in 2011. The Higgs boson mass ranges of 111.4 GeV to 116.6 GeV, 119.4 GeV to 122.1 GeV, and 129.2 GeV to 541 GeV are excluded at the 95% confidence level, while the range 120 GeV to 560 GeV is expected to be excluded in the absence of a signal. An excess of events is observed at Higgs boson mass hypotheses around 126 GeV with a local significance of 2.9 standard deviations (sigma). The global probability for the background to produce an excess at least as significant anywhere in the entire explored Higgs boson mass range of 110-600 GeV is estimated to be similar to 15%, corresponding to a significance of approximately 1 sigma.

Chaos in Schwarzschild spacetime: The motion of a spinning particle

Abstract: We study the motion of a spinning test particle in Schwarzschild spacetime, analyzing the Poincar\'e map and the Lyapunov exponent We find chaotic behavior for a particle with spin higher than some critical value (eg, ${S}_{\mathrm{}\mathrm{cr}}\ensuremath{\sim}0635\ensuremath{\mu}M$ for the total angular momentum $J=4\ensuremath{\mu}M)$, where $\ensuremath{\mu}$ and $M$ are the masses of a particle and of a black hole, respectively The inverse of the Lyapunov exponent in the most chaotic case is about five orbital periods, which suggests that chaos of a spinning particle may become important in some relativistic astrophysical phenomena The ``effective potential'' analysis enables us to classify the particle orbits into four types as follows When the total angular momentum $J$ is large, some orbits are bounded and the ``effective potentials'' are classified into two types: (B1) one saddle point (unstable circular orbit) and one minimal point (stable circular orbit) on the equatorial plane exist for small spin; and (B2) two saddle points bifurcate from the equatorial plane and one minimal point remains on the equatorial plane for large spin When $J$ is small, no bound orbits exist and the potentials are classified into another two types: (U1) no extremal point is found for small spin; and (U2) one saddle point appears on the equatorial plane, which is unstable in the direction perpendicular to the equatorial plane, for large spin The types (B1) and (U1) are the same as those for a spinless particle, but the potentials (B2) and (U2) are new types caused by spin-orbit coupling The chaotic behavior is found only in the type (B2) potential The ``heteroclinic orbit,'' which could cause chaos, is also observed in type (B2)

Polarizations of J/ψ and ψ(2S) mesons produced in pp̄ collisions at s=1.96TeV

Abstract: The authors have measured the polarizations of J/{psi} and {psi}(2S) mesons as functions of their transverse momentum p{sub T} when they are produced promptly in the rapidity range |y| < 0.6 with p{sub T} {ge} 5 GeV/c. The analysis is performed using a data sample with an integrated luminosity of about 800 pb{sup -1} collected by the CDF II detector. For both vector mesons, they find that the polarizations become increasingly longitudinal as p{sub T} increases from 5 to 30 GeV/c. These results are compared to the predictions of non-relativistic quantum chromo-dynamics and other contemporary models. The polarizations of J/{psi} and {psi}(2S) mesons from B-hadron decays are also reported.