13,481 research outputs found
Massive Spin-2 fields of Geometric Origin in Curved Spacetimes
We study the consistency of a model which includes torsion as well as the
metric as dynamical fields and has massive spin-2 particle in its spectrum. The
massive spin-2 mode resides in the torsion, rather than in the metric. It is
known that this model is tachyon- and ghost-free in Minkowski background. We
show that this property remains valid and no other pathologies emerge in de
Sitter and anti-de Sitter backgrounds, with some of our results extending to
arbirary Einstein space backgrounds. This suggests that the model is
consistent, at least at the classical level, unlike, e.g., the Fierz--Pauli
theory.Comment: 17 pages, Clarifying remarks added in section 5, minor changes,
version to be published in the Phys. Rev.
Nuclear Magnetic Relaxation Rate in a Noncentrosymmetric Superconductor
For a noncentrosymmetric superconductor such as CePt3Si, we consider a Cooper
pairing model with a two-component order parameter composed of spin-singlet and
spin-triplet pairing components.
We demonstrate that such a model on a qualitative level accounts for
experimentally observed features of the temperature dependence of the nuclear
spin-lattice relaxation rate 1/T1, namely a peak just below Tc and a line-node
gap behavior at low temperatures.Comment: 4 page
Design and performance of the Thomson scattering diagnostic on LHD
This article describes the design and performance of a multi-point (200) high repetition rate (4×50 Hz) Thomson scattering diagnostic installed on the Large Helical Device. A unique feature of this system is its oblique back scattering configuration, which enables us to observe the entire plasma region along a major radius on the midplane under a severely restricted port constraint. High throughput collection optics using a mosaic mirror of 1.5 m×1.8 m area yield high quality data even with 0.5 J pulse energy delivered from 50 Hz repetition rate Nd: yttrium?aluminum?garnet lasers. High repetition and high spatial resolution (2?4 cm) of the system enable us to study island evolution in the plasma
Active control of laser beam direction for LHD YAG Thomson scattering
We have developed a YAG Thomson scattering (TS) system for the measurements of electron temperature and density profiles on the large helical device (LHD). The LHD-TS has four YAG lasers, and flexible operational modes are possible by using them. For example, (1) high-energy mode: The pulse energy can be increased up to four times by firing the four lasers simultaneously. In this mode, the data quality can be improved for low-density plasmas. (2) High repetition mode: When firing the lasers at intervals of 5 ms, the lasers work as a 200 Hz laser. The laser beams are guided to the LHD by seven steering mirrors. The first mirror is real-time feedback controlled for precise beam transport. The beam pointing stability is improved successfully from 200 μrad to below 4 μrad with the feedback-control system. We describe the details of the laser system for the LHD-TS
Design, construction, and performance of a composite mirror for collecting Thomson scattered light from the large helical device plasma
A 1.5 m×1.8 m rectangular composite mirror composed of 138 segment hexagonal spherical mirrors was constructed for collecting Thomson scattered light from the Large Helical Device plasma. The hexagonal mirrors with side length of 87 mm were patched on the surface of a framework made of glass fiber reinforced plastic. The position and angular orientation of each mirror are adjusted with three pairs of push-and-pull screws attached to the back plane of the mirrors so that the image of a tiny light source (0.1 mm in diameter) formed by each segment mirror be minimized and coincide with each other on a charge coupled device plate. The optical quality and its long-term stability of the assembled mirror have been monitored and sufficient for the present purpose
Path Integral for Space-time Noncommutative Field Theory
The path integral for space-time noncommutative theory is formulated by means
of Schwinger's action principle which is based on the equations of motion and a
suitable ansatz of asymptotic conditions. The resulting path integral has
essentially the same physical basis as the Yang-Feldman formulation. It is
first shown that higher derivative theories are neatly dealt with by the path
integral formulation, and the underlying canonical structure is recovered by
the Bjorken-Johnson-Low (BJL) prescription from correlation functions defined
by the path integral. A simple theory which is non-local in time is then
analyzed for an illustration of the complications related to quantization,
unitarity and positive energy conditions. From the view point of BJL
prescription, the naive quantization in the interaction picture is justified
for space-time noncommutative theory but not for the simple theory non-local in
time. We finally show that the perturbative unitarity and the positive energy
condition, in the sense that only the positive energy flows in the positive
time direction for any fixed time-slice in space-time, are not simultaneously
satisfied for space-time noncommutative theory by the known methods of
quantization.Comment: 21 page
Charge transfer and weak bonding between molecular oxygen and graphene zigzag edges at low temperatures
Electron paramagnetic resonance (EPR) study of air-physisorbed defective
carbon nano-onions evidences in favor of microwave assisted formation of
weakly-bound paramagnetic complexes comprising negatively-charged O2- ions and
edge carbon atoms carrying pi-electronic spins. These complexes being located
on the graphene edges are stable at low temperatures but irreversibly
dissociate at temperatures above 50-60 K. These EPR findings are justified by
density functional theory (DFT) calculations demonstrating transfer of an
electron from the zigzag edge of graphene-like material to oxygen molecule
physisorbed on the graphene sheet edge. This charge transfer causes changing
the spin state of the adsorbed oxygen molecule from S = 1 to S = 1/2 one. DFT
calculations show significant changes of adsorption energy of oxygen molecule
and robustness of the charge transfer to variations of the graphene-like
substrate morphology (flat and corrugated mono- and bi-layered graphene) as
well as edges passivation. The presence of H- and COOH- terminated edge carbon
sites with such corrugated substrate morphology allows formation of ZE-O2-
paramagnetic complexes characterized by small (<50 meV) binding energies and
also explains their irreversible dissociation as revealed by EPR.Comment: 28 pages, 8 figures, 2 tables, accepted in Carbon journa
A Convenient Method of Calibrating Relative Sensitivity of Multi-Channel Thomson Scattering Diagnostic System
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