A Superluminal Subway: The Krasnikov Tube

The ``warp drive'' metric recently presented by Alcubierre has the problem that an observer at the center of the warp bubble is causally separated from the outer edge of the bubble wall. Hence such an observer can neither create a warp bubble on demand nor control one once it has been created. In addition, such a bubble requires negative energy densities. One might hope that elimination of the first problem might ameliorate the second as well. We analyze and generalize a metric, originally proposed by Krasnikov for two spacetime dimensions, which does not suffer from the first difficulty. As a consequence, the Krasnikov metric has the interesting property that although the time for a one-way trip to a distant star cannot be shortened, the time for a round trip, as measured by clocks on Earth, can be made arbitrarily short. In our four dimensional extension of this metric, a ``tube'' is constructed along the path of an outbound spaceship, which connects the Earth and the star. Inside the tube spacetime is flat, but the light cones are opened out so as to allow superluminal travel in one direction. We show that, although a single Krasnikov tube does not involve closed timelike curves, a time machine can be constructed with a system of two non-overlapping tubes. Furthermore, it is demonstrated that Krasnikov tubes, like warp bubbles and traversable wormholes, also involve unphysically thin layers of negative energy density, as well as large total negative energies, and therefore probably cannot be realized in practice.Comment: 20 pages, LATEX, 5 eps figures, uses \eps

An Axial Time-of-flight Mass Spectrometer for Upper Atmospheric Measurements

As the “shoreline” of the Earth’s atmosphere, the mesosphere/lower thermosphere (MLT) region is home to many interesting and important phenomena, the most visible of which are the auroras. Geomagnetic storms, in addition to causing very intense auroral activity, also deposit large amounts of energy into the earth’s ionosphere. Recent analysis of data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument aboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite suggests that 5.3μm emission from vibrationally excited NO is the main method of energy dissipation from energy deposited by geomagnetic storms. Additionally, NO+ has been shown to be the major contributor to geomagnetic storm induced 4.3μm nighttime emission. In order to better physically understand these two large sources of geomagnetic storm energy dissipation, a sounding rocket mission, ROCKet-borne Storm Energetics of Auroral Dosing in the E-region (ROCK-STEADE) is being proposed. The ROCK-STEADE instrument suite consists of several photometers, an interferometer, an IR spectrometer, and two time-of-flight mass spectrometers (TOFMS). The TOFMS will measure the ion and neutral compositions in the atmosphere as the sounding rocket travels through the MLT. Due to the use of microchannel plate (MCP) detectors in TOFMS, one of the major challenges to making measurements in the MLT is the high ambient pressure. Other challenges and sources of error and background include stray UV photons, scattering of gas molecules from the interior surfaces of the instrument, dissociation of molecules in the bow shock caused by the supersonic rocket flight, and reactive recombination at the surfaces of the instrument. Methods of dealing with these challenges include: • Recent advances in MCP technology allowing MCP operation into the mtorr range • Cooling the front surface of the TOFMS using liquid He to eliminate the bow shock (thus making possible the direct sampling of the ambient atmosphere) • Cryogenically cooling the interior of the instrument to eliminate scattering of gas from instrument walls and therefore also reducing the contribution of reactive recombination • Rigorous error analysis to account for the background contribution of stray U

Multiwavelength Constraints on the Day-Night Circulation Patterns of HD 189733b

We present new Spitzer observations of the phase variation of the hot Jupiter HD 189733b in the MIPS 24 μm bandpass, spanning the same part of the planet's orbit as our previous observations in the IRAC 8 μm bandpass (Knutson et al. 2007). We find that the minimum hemisphere-averaged flux from the planet in this bandpass is 76% ± 3% of the maximum flux; this corresponds to minimum and maximum hemisphere-averaged brightness temperatures of 984 ± 48 K and 1220 ± 47 K, respectively. The planet reaches its maximum flux at an orbital phase of 0.396 ± 0.022, corresponding to a hot region shifted 20°-30° east of the substellar point. Because tidally locked hot Jupiters would have enormous day-night temperature differences in the absence of winds, the small amplitude of the observed phase variation indicates that the planet's atmosphere efficiently transports thermal energy from the day side to the night side at the 24 μm photosphere, leading to modest day-night temperature differences. The similarities between the 8 and 24 μm phase curves for HD 189733b lead us to conclude that the circulation on this planet behaves in a fundamentally similar fashion across the range of pressures sensed by these two wavelengths. One-dimensional radiative transfer models indicate that the 8 μm band should probe pressures 2-3 times greater than at 24 μm, although the uncertain methane abundance complicates the interpretation. If these two bandpasses do probe different pressures, it would indicate that the temperature varies only weakly between the two sensed depths, and hence that the atmosphere is not convective at these altitudes. We also present an analysis of the possible contribution of star spots to the time series at both 8 and 24 μm based on near-simultaneous ground-based observations and additional Spitzer observations. Accounting for the effects of these spots results in a slightly warmer night-side temperature for the planet in both bandpasses, but does not otherwise affect our conclusions

Magnetic Fields from Phase Transitions

The generation of primordial magnetic fields from cosmological phase transitions is discussed, paying particular attention to the electroweak transition and to the various definitions of the `average' field that have been put forward. It is emphasised that only the volume average has dynamical significance as a seed for galactic dynamos. On rather general grounds of causality and energy conservation, it is shown that, in the absence of MHD effects that transfer power in the magnetic field from small to large scales, processes occurring at the electroweak transition cannot generate fields stronger than $10^{-20}$ Gauss on a scale of 0.5 Mpc. However, it is implausible that this upper bound could ever be reached, as it would require all the energy in the Universe to be turned into a magnetic field coherent at the horizon scale. Non-linear MHD effects seem therefore to be necessary if the electroweak transition is to create a primordial seed field.Comment: 6pp RevTeX. Correct finished version supplie

Averaged Methods for Vortex-String Evolution

We discuss friction-dominated vortex-string evolution using a new analytic model recently developed by the authors. By treating the average string velocity, as well as the characteristic lengthscale, as dynamical variables, we can provide a quantitative picture of the complete evolution of a vortex-string network. Previously known scaling laws are confirmed, and new quantitative predictions regarding loop production and evolution are made.Comment: REVTeX, 21 pages, 23 .eps files included. Submitted to Phys. Rev. B. Minor changes---but some key concepts clarifie

Continuum Halos in Nearby Galaxies -- an EVLA Survey (CHANG-ES) -- I: Introduction to the Survey

We introduce a new survey to map the radio continuum halos of a sample of 35 edge-on spiral galaxies at 1.5 GHz and 6 GHz in all polarization products. The survey is exploiting the new wide bandwidth capabilities of the Karl G. Jansky Very Large Array (i.e. the Expanded Very Large Array, or EVLA) in a variety of array configurations (B, C, and D) in order to compile the most comprehensive data set yet obtained for the study of radio halo properties. This is the first survey of radio halos to include all polarization products. In this first paper, we outline the scientific motivation of the survey, the specific science goals, and the expected improvements in noise levels and spatial coverage from the survey. Our goals include investigating the physical conditions and origin of halos, characterizing cosmic ray transport and wind speed, measuring Faraday rotation and mapping the magnetic field, probing the in-disk and extraplanar far-infrared - radio continuum relation, and reconciling non-thermal radio emission with high-energy gamma-ray models. The sample size allows us to search for correlations between radio halos and other properties, including environment, star formation rate, and the presence of AGNs. In a companion paper (Paper II) we outline the data reduction steps and present the first results of the survey for the galaxy, NGC 4631.Comment: 17 pages, 1 figure, accepted to the Astronomical Journal, Version 2 changes: added acknowledgement to NRA

1971: Abilene Christian College Bible Lectures - Full Text

WORLD EVANGELISM Being the Abilene Christian College Annual Bible Lectures 1971 Published by ABILENE CHRISTIAN COLLEGE BOOK STORE ACC Station Abilene, Texas 7960

Fermionic massive modes along cosmic strings

The influence on cosmic string dynamics of fermionic massive bound states propagating in the vortex, and getting their mass only from coupling to the string forming Higgs field, is studied. Such massive fermionic currents are numerically found to exist for a wide range of model parameters and seen to modify drastically the usual string dynamics coming from the zero mode currents alone. In particular, by means of a quantization procedure, a new equation of state describing cosmic strings with any kind of fermionic current, massive or massless, is derived and found to involve, at least, one state parameter per trapped fermion species. This equation of state exhibits transitions from subsonic to supersonic regimes while the massive modes are filled.Comment: 27 pages, 15 figures, uses ReVTeX. Shortened version, accepted for publication in Phys. Rev.

SPT-3G: A Next-Generation Cosmic Microwave Background Polarization Experiment on the South Pole Telescope

We describe the design of a new polarization sensitive receiver, SPT-3G, for the 10-meter South Pole Telescope (SPT). The SPT-3G receiver will deliver a factor of ~20 improvement in mapping speed over the current receiver, SPTpol. The sensitivity of the SPT-3G receiver will enable the advance from statistical detection of B-mode polarization anisotropy power to high signal-to-noise measurements of the individual modes, i.e., maps. This will lead to precise (~0.06 eV) constraints on the sum of neutrino masses with the potential to directly address the neutrino mass hierarchy. It will allow a separation of the lensing and inflationary B-mode power spectra, improving constraints on the amplitude and shape of the primordial signal, either through SPT-3G data alone or in combination with BICEP-2/KECK, which is observing the same area of sky. The measurement of small-scale temperature anisotropy will provide new constraints on the epoch of reionization. Additional science from the SPT-3G survey will be significantly enhanced by the synergy with the ongoing optical Dark Energy Survey (DES), including: a 1% constraint on the bias of optical tracers of large-scale structure, a measurement of the differential Doppler signal from pairs of galaxy clusters that will test General Relativity on ~200 Mpc scales, and improved cosmological constraints from the abundance of clusters of galaxies.Comment: 21 pages, 9 figures. To be published in Proceedings of SPIE Volume 9153. Presented at SPIE Astronomical Telescopes + Instrumentation 2014, conference 915