75 research outputs found
Classical Solutions of Ghost Condensation Models
Motivated by ideas obtained from both ghost condensation and gravitational
Higgs mechanism, we attempt to find classical solutions in the unitary gauge in
general ghost condensation models. It is shown that depending on the form of
scalar fields in an action, there are three kinds of exact solutions, which are
(anti-) de Sitter space-time, polynomially expanding universes and flat
Minkowski space-time. We briefly comment on gravitational Higgs mechanism in
these models where we have massive gravitons of 5 degrees of freedom and 1
unitary scalar field (Nambu-Goldstone boson) after spontaneous symmetry
breakdown of general coordinate reparametrization invariance. The models at
hand are free from the problem associated with the non-unitary propagating
mode.Comment: 9 pages, no figure
Modes in Light-Cone Quantization
We investigate the light-cone quantization of theory in 1+1
dimensions with a regularization of discretized light-cone momentum .
Solving a second-class constraint associated with the mode, we show
that the mode propagates along the internal lines of Feynman diagrams
in any order of perturbation, hence our theory recovers the Lorentz invariance.Comment: 14p
Nickel-based phosphide superconductor with infinite-layer structure, BaNi2P2
Analogous to cuprate high-Tc superconductors, a NiP-based compound system has
several crystals in which the Ni-P layers have different stacking structures.
Herein, the properties of BaNi2P2 are reported. BaNi2P2 has an infinite-layer
structure, and shows a superconducting transition at ~3 K. Moreover, it
exhibits metallic conduction and Pauli paramagnetism in the temperature range
of 4-300 K. Below 3 K, the resistivity sharply drops to zero, and the magnetic
susceptibility becomes negative, while the volume fraction of the
superconducting phase estimated from the diamagnetic susceptibility reaches
~100 vol.% at 1.9 K. These observations substantiate that BaNi2P2 is a bulk
superconductor.Comment: 9 pages, 4 figures, Solid State Communications, in press. Received 4
March 2008. Accepted 2 May 2008. Available online 14 May 200
Massive Gravity in Curved Cosmological Backgrounds
We study the physical propagating modes in a massive gravity model in curved
cosmological backgrounds, which we have found as classical solutions in our
previous paper. We show that, generically, there exist such the cosmological
background solutions consistent with the equations of motion where we assume
the ghost condensation ansatzes. Using the (1+3)-parametrization of the metric
fluctuations with 'unitary' gauge, we find that there is neither a scalar ghost
nor a tachyon in the spectrum of the propagating modes, the tensor modes become
massive owing to gravitational Higgs mechanism, and the model is free of the
Boulware-Deser instability. The price we have to pay is that the scalar sector
breaks the Lorentz-invariance, but there are no pathologies in the spectrum and
lead to interesting phenomenology. Moreover, we present a proof of the absence
of non-unitary modes for a specific ghost condensation model in a cosmological
background.Comment: 20 page
Integrated radiation monitoring and interlock system for the LHD deuterium experiments
The Large Helical Device (LHD) successfully started the deuterium experiment in March 2017, in which further plasma performance improvement is envisaged to provide a firm basis for the helical reactor design. Some major upgrades of facilities have been made for safe and productive deuterium experiments. For radiation safety, the tritium removal system, the integrated radiation monitoring system, and the access control system have been newly installed. Each system has new interlock signals that will prevent any unsafe plasma operation or plant condition. Major interlock extensions have been implemented as a part of the integrated radiation monitoring system, which also has an inter-connection to the LHD central operation and control system. The radiation monitoring system RMSAFE (Radiation Monitoring System Applicable to Fusion Experiments) is already operating for monitoring γ(X)-rays in LHD. Some neutron measurements have been additionally applied for the deuterium experiments. The LHD data acquisition system LABCOM can acquire and process 24 h every day continuous data streams. Since γ(X)-ray and neutron measurements require higher availability, the sensors, controllers, data acquisition computers, network connections, and visualization servers have been designed to be duplicated or multiplexed for redundancy. The radiation monitoring displays in the LHD control room have been carefully designed to have excellent visual recognition, and to make users immediately aware of several alerts regarding the dose limits. The radiation safety web pages have been also upgraded to always show both dose rates of γ(X)-rays and neutrons in real time
- …