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

Newtonian and Relativistic Cosmologies

Cosmological N-body simulations are now being performed using Newtonian gravity on scales larger than the Hubble radius. It is well known that a uniformly expanding, homogeneous ball of dust in Newtonian gravity satisfies the same equations as arise in relativistic FLRW cosmology, and it also is known that a correspondence between Newtonian and relativistic dust cosmologies continues to hold in linearized perturbation theory in the marginally bound/spatially flat case. Nevertheless, it is far from obvious that Newtonian gravity can provide a good global description of an inhomogeneous cosmology when there is significant nonlinear dynamical behavior at small scales. We investigate this issue in the light of a perturbative framework that we have recently developed, which allows for such nonlinearity at small scales. We propose a relatively straightforward "dictionary"---which is exact at the linearized level---that maps Newtonian dust cosmologies into general relativistic dust cosmologies, and we use our "ordering scheme" to determine the degree to which the resulting metric and matter distribution solve Einstein's equation. We find that Einstein's equation fails to hold at "order 1" at small scales and at "order $\epsilon$" at large scales. We then find the additional corrections to the metric and matter distribution needed to satisfy Einstein's equation to these orders. While these corrections are of some interest in their own right, our main purpose in calculating them is that their smallness should provide a criterion for the validity of the original dictionary (as well as simplified versions of this dictionary). We expect that, in realistic Newtonian cosmologies, these additional corrections will be very small; if so, this should provide strong justification for the use of Newtonian simulations to describe relativistic cosmologies, even on scales larger than the Hubble radius.Comment: 35 pages; minor change

Empathic ability and perceptual disposition.

Thesis (Ph.D.)--Boston UniversityThe purpose of this study was to investigate the relationship between two variables: empathic ability, the ability to perceive another person as that person perceives himself; and perceptual disposition, the characteristic organization of the perceptual-cognitive response pattern. Theoretically, both variables are related to psychological adjustment. With respect to process, a relationship between the variables is assumed in terms of the observer's flexibility in selecting phenomena for interpretation and in forming and revising interpretative hypotheses in the direction of the subject's own frame of reference. [TRUNCATED] It is concluded that there is a relationship between empathic ability and perceptual disposition as presently defined. In view of the homogeneity of the experimental population, no generalization beyond this group and its characteristics is actually warranted by the present findings. Also, the many factors which may be involved in actual interaction between observer and subject are absent in the present experiment, and must be considered in applying the present findings to the empathic process as it operates in everyday life. Two lines of future research are suggested. One is the exploration of the content of predictive hypotheses made by successful and unsuccessful observers, and by the different perceptual disposition groups. The second is the investigation of the etiological correlates of the perceptual dispositions. For clinical psychology, the overall aim of such research would be to study learning readiness in interpersonal relationships as it relates to psychological health

Probing fundamental physics with pulsars

Pulsars provide a wealth of information about General Relativity, the equation of state of superdense matter, relativistic particle acceleration in high magnetic fields, the Galaxy's interstellar medium and magnetic field, stellar and binary evolution, celestial mechanics, planetary physics and even cosmology. The wide variety of physical applications currently being investigated through studies of radio pulsars rely on: (i) finding interesting objects to study via large-scale and targeted surveys; (ii) high-precision timing measurements which exploit their remarkable clock-like stability. We review current surveys and the principles of pulsar timing and highlight progress made in the rotating radio transients, intermittent pulsars, tests of relativity, understanding pulsar evolution, measuring neutron star masses and the pulsar timing array.Comment: 6 pages, 1 figure, to appear in the proceedings of IAU XXVII GA - JD3 - Neutron Stars: Timing in Extreme Environments XXVII IAU General Assembly, Rio de Janeiro, Brazil, 3-14 August 200

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

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