3,052 research outputs found
Gravitational radiation from extreme Kerr black hole
Gravitational radiation induced by a test particle falling into an extreme Kerr black hole was investigated analytically. Assuming the radiation is dominated by the infinite sequence of quasi-normal modes which has the limiting frequency m/(2M), where m is an azimuthal eigenvalue and M is the mass of the black hole, it was found that the radiated energy diverges logarithmically in time. Then the back reaction to the black hole was evaluated by appealing to the energy and angular momentum conservation laws. It was found that the radiation has a tendency to increase the ratio of the angular momentum to mass of the black hole, which is completely different from non-extreme case, while the contribution of the test particle is to decrease it
Weak Decay of in Nuclei: Direct Quark Mechanism vs Meson Exchange
Nonmesonic decays of in nuclear medium and light hypernuclei are
studied by using the weak transition potential derived from
the meson exchange mechanism and the direct quark mechanism. The long range
part of the transition potential is described by exchanges of the pseudoscalar
mesons (, , ), while the vector mesons (, ,
) may be considered as the medium- and short-range part in the meson
exchange picture. We propose the direct quark transition potential as the short
range part, which is derived from the matrix elements of the
effective weak Hamiltonian in the two baryon states. The results indicate that
the direct quark contribution is significantly large and its behavior is
qualitatively different from the vector meson exchanges. We also find that the
decay rate is sensitive to the choice of form factor and that a soft cutoff
must be used for the pion-baryon verteces so that the strong tensor transition
is suppressed. We find that the results are compatible with
experiment although the ratio is still too large. The decays of
light hypernuclei are related to the \DI=3/2 amplitudes of the nonmesonic
decay. The role of chiral symmetry for the pionic decays are discussed.Comment: 10 pages, Talk presented by Makoto Oka at the APCTP Workshop on
Strangeness Nuclear Physics (SNP'99), February, 199
Observation of Hysteretic Transport Due to Dynamic Nuclear Spin Polarization in a GaAs Lateral Double Quantum Dot
We report a new transport feature in a GaAs lateral double quantum dot that
emerges only for magnetic field sweeps and shows hysteresis due to dynamic
nuclear spin polarization (DNP). This DNP signal appears in the Coulomb
blockade regime by virtue of the finite inter-dot tunnel coupling and
originates from the crossing between ground levels of the spin triplet and
singlet extensively used for nuclear spin manipulations in pulsed gate
experiments. The unexpectedly large signal intensity is suggestive of
unbalanced DNP between the two dots, which opens up the possibility of
controlling electron and nuclear spin states via DC transport.Comment: 5 pages, 4 figure
Reconstruction of primordial tensor power spectra from B-mode polarization of the cosmic microwave background
Given observations of B-mode polarization power spectrum of the cosmic
microwave background (CMB), we can reconstruct power spectra of primordial
tensor modes from the early Universe without assuming their functional form
such as a power-law spectrum. Shape of the reconstructed spectra can then be
used to probe the origin of tensor modes in a model-independent manner. We use
the Fisher matrix to calculate the covariance matrix of tensor power spectra
reconstructed in bins. We find that the power spectra are best reconstructed at
wavenumbers in the vicinity of and , which correspond to the "reionization bump" at
and "recombination bump" at of the CMB B-mode
power spectrum, respectively. The error bar between these two wavenumbers is
larger because of lack of the signal between the reionization and recombination
bumps. The error bars increase sharply towards smaller (larger) wavenumbers
because of the cosmic variance (CMB lensing and instrumental noise). To
demonstrate utility of the reconstructed power spectra we investigate whether
we can distinguish between various sources of tensor modes including those from
the vacuum metric fluctuation and SU(2) gauge fields during single-field
slow-roll inflation, open inflation and massive gravity inflation. The results
depend on the model parameters, but we find that future CMB experiments are
sensitive to differences in these models. We make our calculation tool
available on-line.Comment: 9 pages, 2 figures, 4 tables; accepted version in Phys. Rev.
A solution for secure use of Kibana and Elasticsearch in multi-user environment
Monitoring is indispensable to check status, activities, or resource usage of
IT services. A combination of Kibana and Elasticsearch is used for monitoring
in many places such as KEK, CC-IN2P3, CERN, and also non-HEP communities.
Kibana provides a web interface for rich visualization, and Elasticsearch is a
scalable distributed search engine. However, these tools do not support
authentication and authorization features by default. In the case of single
Kibana and Elasticsearch services shared among many users, any user who can
access Kibana can retrieve other's information from Elasticsearch. In
multi-user environment, in order to protect own data from others or share part
of data among a group, fine-grained access control is necessary.
The CERN cloud service group had provided cloud utilization dashboard to each
user by Elasticsearch and Kibana. They had deployed a homemade Elasticsearch
plugin to restrict data access based on a user authenticated by the CERN Single
Sign On system. It enabled each user to have a separated Kibana dashboard for
cloud usage, and the user could not access to other's one. Based on the
solution, we propose an alternative one which enables user/group based
Elasticsearch access control and Kibana objects separation. It is more flexible
and can be applied to not only the cloud service but also the other various
situations. We confirmed our solution works fine in CC-IN2P3. Moreover, a
pre-production platform for CC-IN2P3 has been under construction.
We will describe our solution for the secure use of Kibana and Elasticsearch
including integration of Kerberos authentication, development of a Kibana
plugin which allows Kibana objects to be separated based on user/group, and
contribution to Search Guard which is an Elasticsearch plugin enabling
user/group based access control. We will also describe the effect on
performance from using Search Guard.Comment: International Symposium on Grids and Clouds 2017 (ISGC 2017
- …