A Primeval Magellanic Stream and Others

The Magellanic Stream might have grown out of tidal interactions at high redshift, when the young galaxies were close together, rather than from later interactions among the Magellanic Clouds and Milky Way. This is illustrated in solutions for the orbits of Local Group galaxies under the cosmological condition of growing peculiar velocities at high redshift. Massless test particles initially near and moving with the Large Magellanic Cloud in these solutions end up with distributions in angular position and redshift similar to the Magellanic Stream, though with the usual overly prominent leading component that the Milky Way corona might have suppressed. Another possible example of the effect of conditions at high redshift is a model primeval stream around the Local Group galaxy NGC 6822. Depending on the solution for Local Group dynamics this primeval stream can end up with position angle similar to the HI around this galaxy, and a redshift gradient in the observed direction. The gradient is much smaller than observed, but might have been increased by dissipative contraction. Presented also is an even more speculative illustration of the possible effect of initial conditions, primeval stellar streams around M31.Comment: 23 pages, 7 figure

Holographic field theory models of dark energy in interaction with dark matter

We discuss two lagrangian interacting dark energy models in the context of the holographic principle. The potentials of the interacting fields are constructed. The models are compared with CMB distance information, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. For both models the results are consistent with a non vanishing interaction between dark sectors - with more than three standard deviations of confidence for one of them. Moreover, in both cases, the sign of coupling is consistent with dark energy decaying into dark matter, alleviating the coincidence problem.Comment: arXiv admin note: substantial text overlap with arXiv:0912.399

Skewness as a probe of non-Gaussian initial conditions

We compute the skewness of the matter distribution arising from non-linear evolution and from non-Gaussian initial perturbations. We apply our result to a very generic class of models with non-Gaussian initial conditions and we estimate analytically the ratio between the skewness due to non-linear clustering and the part due to the intrinsic non-Gaussianity of the models. We finally extend our estimates to higher moments.Comment: 5 pages, 2 ps-figs., accepted for publication in PRD, rapid com

Issues for the Next Generation of Galaxy Surveys

I argue that the weight of the available evidence favours the conclusions that galaxies are unbiased tracers of mass, the mean mass density (excluding a cosmological constant or its equivalent) is less than the critical Einstein-de Sitter value, and an isocurvature model for structure formation offers a viable and arguably attractive model for the early assembly of galaxies. If valid these conclusions complicate our work of adding structure formation to the standard model for cosmology, but it seems sensible to pay attention to evidence.Comment: 14 pages, 3 postscript figures, uses rspublic.st

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

Effects of P-wave Annihilation on the Angular Power Spectrum of Extragalactic Gamma-rays from Dark Matter Annihilation

We present a formalism for estimating the angular power spectrum of extragalactic gamma-rays produced by dark matter annihilating with any general velocity-dependent cross section. The relevant density and velocity distribution of dark matter is modeled as an ensemble of smooth, universal, rigid, disjoint, spherical halos with distribution and universal properties constrained by simulation data. We apply this formalism to theories of dark matter with p-wave annihilation, for which the relative-velocity-weighted annihilation cross section is \sigma v=a+bv^2. We determine that this significantly increases the gamma-ray power if b/a >> 10^6. The effect of p-wave annihilation on the angular power spectrum is very similar for the sample of particle physics models we explored, suggesting that the important effect for a given b/a is largely determined by the cosmic dark matter distribution. If the dark matter relic from strong p-wave theories is thermally produced, the intensities of annihilation gamma-rays are strongly p-wave suppressed, making them difficult to observe. If an angular power spectrum consistent with a strong p-wave were to be observed, it would likely indicate non-thermal production of dark matter in the early Universe.Comment: 20 pages, 3 figure