Dynamics of a Dark Matter Field with a Quartic Self-Interaction Potential

It may prove useful in cosmology to understand the behavior of the energy distribution in a scalar field that interacts only with gravity and with itself by a pure quartic potential, because if such a field existed it would be gravitationally produced, as a squeezed state, during inflation. It is known that the mean energy density in such a field after inflation varies with the expansion of the universe in the same way as radiation. I show that if the field initially is close to homogeneous, with small energy density contrast delta rho /rho and coherence length L, the energy density fluctuations behave like acoustic oscillations in an ideal relativistic fluid for a time on the order of L/|delta rho /rho|. This ends with the appearance of features that resemble shock waves, but interact in a close to elastic way that reversibly disturbs the energy distribution.Comment: 7 pages, 5 figures, submitted to Phys Rev

Dynamics of gas bubbles in an oscillating pressure field Annual report, Jul. 1965 - Aug. 1966

Gas bubble dynamics in oscillating pressure fiel

The finite element machine: An experiment in parallel processing

The finite element machine is a prototype computer designed to support parallel solutions to structural analysis problems. The hardware architecture and support software for the machine, initial solution algorithms and test applications, and preliminary results are described

Cosmological Density Perturbations with a Scale-Dependent Newton's G

We explore possible cosmological consequences of a running Newton's constant $G ( \Box )$, as suggested by the non-trivial ultraviolet fixed point scenario in the quantum field-theoretic treatment of Einstein gravity with a cosmological constant term. In particular we focus here on what possible effects the scale-dependent coupling might have on large scale cosmological density perturbations. Starting from a set of manifestly covariant effective field equations derived earlier, we systematically develop the linear theory of density perturbations for a non-relativistic, pressure-less fluid. The result is a modified equation for the matter density contrast, which can be solved and thus provides an estimate for the growth index parameter $\gamma$ in the presence of a running $G$. We complete our analysis by comparing the fully relativistic treatment with the corresponding results for the non-relativistic (Newtonian) case, the latter also with a weakly scale dependent $G$.Comment: 54 pages, 4 figure

RMS Radio Source Contributions to the Microwave Sky

Cross-correlations of the WMAP full sky K, Ka, Q, V, and W band maps with the 1.4 GHz NVSS source count map and the HEAO I A2 2-10 keV full sky X-ray flux map are used to constrain rms fluctuations due to unresolved microwave sources in the WMAP frequency range. In the Q band (40.7 GHz), a lower limit, taking account of only those fluctuations correlated with the 1.4 GHz radio source counts and X-ray flux, corresponds to an rms Rayleigh-Jeans temperature of ~ 2 microKelvin for a solid angle of one square degree. The correlated fluctuations at the other bands are consistent with a beta = -2.1 +- 0.4 frequency spectrum. Using the rms fluctuations of the X-ray flux and radio source counts, and the cross-correlation of these two quantities as a guide, the above lower limit leads to a plausible estimate of ~ 5 microKelvin for Q-band rms fluctuations in one square degree. This value is similar to that implied by the excess, small angular scale fluctuations observed in the Q band by WMAP, and is consistent with estimates made by extrapolating low-frquency source counts.Comment: 17 pages, 8 figures, submitted to Ap

Materials for Advanced Turbine Engines

An attempt was made to improve methods for producing powder metallurgy aircraft gas turbine engine parts from the nickel base superalloy known as Rene 95. The parts produced were the high pressure turbine aft shaft for the CF6-50 engine and the stages 5 through 9 compressor disk forgings for the CFM56/F101 engines. A 50% cost reduction was achieved as compared to conventional cast and wrought processing practices. An integrated effort involving several powder producers and a major forging source were included

Interaction between Faraday rotation and Cotton-Mouton effects in polarimetry modeling for NSTX

The evolution of electromagnetic wave polarization is modeled for propagation in the major radial direction in the National Spherical Torus Experiment (NSTX) with retroreflection from the center stack of the vacuum vessel. This modeling illustrates that the Cotton-Mouton effect-elliptization due to the magnetic field perpendicular to the propagation direction-is shown to be strongly weighted to the high-field region of the plasma. An interaction between the Faraday rotation and Cotton-Mouton effects is also clearly identified. Elliptization occurs when the wave polarization direction is neither parallel nor perpendicular to the local transverse magnetic field. Since Faraday rotation modifies the polarization direction during propagation, it must also affect the resultant elliptization. The Cotton-Mouton effect also intrinsically results in rotation of the polarization direction, but this effect is less significant in the plasma conditions modeled. The interaction increases at longer wavelength, and complicates interpretation of polarimetry measurements.Comment: Contributed paper published as part of the Proceedings of the 18th Topical Conference on High-Temperature Plasma Diagnostics, Wildwood, New Jersey, May, 201

Cosmological Baryon Sound Waves Coupled with the Primeval Radiation

The fluid equations for the baryon-electron system in an expanding universe are derived from the Boltzmann equation. The effect of the Compton interaction is taken into account properly in order to evaluate the photon-electron collisional term. As an application, the acoustic motions of the baryon-electron system after recombination are investigated. The effective adiabatic index $\gamma$ is computed for sound waves of various wavelengths, assuming the perturbation amplitude is small. The oscillations are found to be dumped when $\gamma$ changes from between 1 (for an isothermal process) to 5/3 (for an adiabatic process).Comment: 20 pages, Revtex, Accepted for publication in Phys. Rev.

Neutrino Mass and Dark Energy from Weak Lensing

Weak gravitational lensing of background galaxies by intervening matter directly probes the mass distribution in the universe. This distribution, and its evolution at late times, is sensitive to both the dark energy, a negative pressure energy density component, and neutrino mass. We examine the potential of lensing experiments to measure features of both simultaneously. Focusing on the radial information contained in a future deep 4000 square degree survey, we find that the expected (1-sigma) error on a neutrino mass is 0.1 eV, if the dark energy parameters are allowed to vary. The constraints on dark energy parameters are similarly restrictive, with errors on w of 0.09. Much of the restrictive power on the dark energy comes not from the evolution of the gravitational potential but rather from how distances vary as a function of redshift in different cosmologies

Is Cosmology Solved?

We have fossil evidence from the thermal background radiation that our universe expanded from a considerably hotter denser state. We have a well defined and testable description of the expansion, the relativistic Friedmann-Lemaitre model. Its observational successes are impressive but I think hardly enough for a convincing scientific case. The lists of observational constraints and free hypotheses within the model have similar lengths. The scorecard on the search for concordant measures of the mass density parameter and the cosmological constant shows that the high density Einstein-de Sitter model is challenged, but that we cannot choose between low density models with and without a cosmological constant. That is, the relativistic model is not strongly overconstrained, the usual test of a mature theory. Work in progress will greatly improve the situation and may at last yield a compelling test. If so, and the relativistic model survives, it will close one line of research in cosmology: we will know the outlines of what happened as our universe expanded and cooled from high density. It will not end research: some of us will occupy ourselves with the details of how galaxies and other large-scale structures came to be the way they are, others with the issue of what our universe was doing before it was expanding. The former is being driven by rapid observational advances. The latter is being driven mainly by theory, but there are hints of observational guidance.Comment: 13 pages, 3 figures. To be published in PASP as part of the proceedings of the Smithsonian debate, Is Cosmology Solved