Cuscuton: A Causal Field Theory with an Infinite Speed of Sound

We introduce a model of scalar field dark energy, Cuscuton, which can be realized as the incompressible (or infinite speed of sound) limit of a scalar field theory with a non-canonical kinetic term (or k-essence). Even though perturbations of Cuscuton propagate superluminally, we show that they have a locally degenerate phase space volume (or zero entropy), implying that they cannot carry any microscopic information, and thus the theory is causal. Even coupling to ordinary scalar fields cannot lead to superluminal signal propagation. Furthermore, we show that the family of constant field hypersurfaces are the family of Constant Mean Curvature (CMC) hypersurfaces, which are the analogs of soap films (or soap bubbles) in a Euclidian space. This enables us to find the most general solution in 1+1 dimensions, whose properties motivate conjectures for global degeneracy of the phase space in higher dimensions. Finally, we show that the Cuscuton action can model the continuum limit of the evolution of a field with discrete degrees of freedom and argue why it is protected against quantum corrections at low energies. While this paper mainly focuses on interesting features of Cuscuton in a Minkowski spacetime, a companion paper (astro-ph/0702002) examines cosmology with Cuscuton dark energy.Comment: 11 pages, 1 figure, added discussion of "coupled cuscuton", matches the published version in PR

Nozzle Wear and Pressure Rise in Heating Volume of Self-blast Type Ultra-high Pressure Nitrogen Arc

This paper reports on experiments with ultra-high pressure nitrogen arcs in a self-blast type switch design. The effect of filling pressure on nozzle mass loss and pressure-rise in the heating volume were investigated. An arc current peak of 130 A at 190 Hz and a fixed inter-electrode gap of 50 mm were used throughout the experiment. The arc burns inside a polytetrafluoroethylene nozzle with a gas outflow vent in the middle. Nitrogen filling pressure of 1 bar, 20 bar, and 40 bar was tested, which also covers the supercritical region. Moreover, to study the effect of vent size on blow pressure near current zero, three different vent dimensions were investigated. By increasing the filling pressure, the energy deposited in the arc increases as a result of increased arcing voltage. It was observed that the pressure-rise in the heating volume is linked to the filling pressure, while the vent size plays a crucial role in the blow pressure near current zero. The nozzle mass loss per unit energy deposited in the arc is found to be independent of the filling pressure

Experimental investigation of dielectric barrier impact on breakdown voltage enhancement of copper wire-plane electrode systems

Non-pressurized air is extensively used as basic insulation media in medium / high voltage equipments. An inherent property of air-insulated designs is that the systems tend to become physically large. Application of Dielectric barrier can increase the breakdown voltage and therefore decrease the size of the equipments. In this paper, the impact of dielectric barrier on breakdown voltage enhancement of a copper wire-plane system is investigated. For this purpose, the copper wire is covered with different dielectric materials. Depending on the air gap and dielectric strength of the barrier the breakdown can be initiated in the solid or gas dielectric. Theoretically, free charges are affected by the electric field between the electrodes and accumulated at the dielectric surface, this leads to the reduction of electric field in air gap and enhancement of the ifield in the dielectric layer. Therefore, with appropriate selection of the barrier thickness and material, it is possible to increase the breakdown voltage of the insulation system. The influence of different parameters like inter-electrode spacing, and dielectric material on the break-down voltage is investigated for applied 50 Hz AC and DC voltages. The results indicate that up to 240% increase of the breakdown voltage can be achieved

CMB B-mode polarization from Thomson scattering in the local universe

[Abridged] The polarization of the CMB is widely recognized as a potential source of information about primordial gravitational waves. The gravitational wave contribution can be separated from the dominant CMB polarization created by density perturbations because it generates both E and B polarization modes, whereas the density perturbations create only E polarization. The limits of our ability to measure gravitational waves are thus determined by statistical and systematic errors, foregrounds, and nonlinear evolution effects such as lensing of the CMB. Usually it is assumed that most foregrounds can be removed because of their frequency dependence, however Thomson scattering of the CMB quadrupole by electrons in the Galaxy or nearby structures shares the blackbody frequency dependence of the CMB. If the optical depth from these nearby electrons is anisotropic, the polarization generated can include B modes even without tensor perturbations. We estimate this effect for the Galactic disk and nearby extragalactic structures, and find that it contributes to the B polarization at the level of ~(1--2)x10^-4\mu K per logarithmic interval in multipole L for L<30. This is well below the detectability level even for a future CMB polarization satellite. Depending on its structure and extent, the Galactic corona may be a source of B-modes comparable to the residual large-scale lensing B-mode after the latter has been cleaned using lensing reconstruction techniques. For an extremely ambitious post-Planck CMB experiment, Thomson scattering in the Galactic corona is thus a potential contaminant of the gravitational wave signal; conversely, if the other foregrounds can be cleaned out, such an experiment might be able to constrain models of the corona.Comment: 10 pages, 4 figures, to be submitted to Phys. Rev.

Cross-Correlation of the Cosmic Microwave Background with the 2MASS Galaxy Survey: Signatures of Dark Energy, Hot Gas, and Point Sources

We cross-correlate the Cosmic Microwave Background (CMB) temperature anisotropies observed by the Wilkinson Microwave Anisotropy Probe (WMAP) with the projected distribution of extended sources in the Two Micron All Sky Survey (2MASS). By modelling the theoretical expectation for this signal, we extract the signatures of dark energy (Integrated Sachs-Wolfe effect;ISW), hot gas (thermal Sunyaev-Zeldovich effect;thermal SZ), and microwave point sources in the cross-correlation. Our strongest signal is the thermal SZ, at the 3.1-3.7 \sigma level, which is consistent with the theoretical prediction based on observations of X-ray clusters. We also see the ISW signal at the 2.5 \sigma level, which is consistent with the expected value for the concordance LCDM cosmology, and is an independent signature of the presence of dark energy in the universe. Finally, we see the signature of microwave point sources at the 2.7 \sigma level.Comment: 35 pages (preprint format), 8 figures. In addition to minor revisions based on referee's comments, after correcting for a bug in the code, the SZ detection is consistent with the X-ray observations. Accepeted for publication in Physical Review

Statistical Characteristics of the Output Voltage in Compact Marx Generators

Compact Marx generators are widely used as portable pulse generator in different industrial applications, where high power pulses with rise times of order of some tens of nanoseconds are needed. For those applications, closing switches with very short delay and jitter times have to be used. Considering the fact that the breakdown of spark gap is a statistical process, the delay times of the closing switches are statistical voltage-dependent parameters. As a result, the characteristics of the output voltage of the Marx generator, i.e. its amplitude and rise time, are also statistical parameters. In this paper, taking the statistical behaviour of the breakdown process in spark gaps into consideration, the statistical characteristics of the output voltage have been studied in detail