6,172 research outputs found
The WIMP capture process for dark stars in the early universe
The first stars to form in the universe may have been dark stars, powered by
dark matter annihilation instead of nuclear fusion. The initial amount of dark
matter gathered by the star gravitationally can sustain it only for a limited
period of time. It has been suggested that capture of additional dark matter
from the environment can prolong the dark star phase even to the present day.
Here we show that this capture process is ineffective to prolong the life of
the first generation of dark stars. We construct a Monte-Carlo simulation that
follows each Weakly Interacting Massive Particle (WIMP) in the dark matter halo
as its orbit responds to the formation and evolution of the dark star, as it
scatters off the star's nuclei, and as it annihilates inside the star. A rapid
depletion of the WIMPs on orbits that cross the star causes the demise of the
first generation of dark stars. We suggest that a second generation of dark
stars may in principle survive much longer through capture. We comment on the
effect of relaxing our assumptions.Comment: 13 pages, 6 figure
New State Records for the Cicada Parasite Beetle Sandalus petrophya Knoch (Rhipiceridae)
Abstract: New state records are presented for Sandalus petrophya specimens from Nebraska and Iowa along with the currently known distribution of this beetle species
Trawl-induced Damage to Sponges Observed From a Research Submersible
Three experimental trawl paths subjected to a single pass with the trawl in 1996 in about 200 m of water on the eastern Gulf of Alaska continental shelf were revisited in July 1997, 1 year post-trawl. Many large, erect sponges, the taxa impacted most significantly, had been removed or damaged by the trawl. Sponges in the cold, deep water of the Gulf of Alaska were slow to recover from trawling effects. These findings contrast with recovery times for shallow, warmwater sponges and may have fishery management implications for cold-water regions
Review of Observational Evidence for Dark Matter in the Universe and in upcoming searches for Dark Stars
Over the past decade, a consensus picture has emerged in which roughly a
quarter of the universe consists of dark matter. The observational evidence for
the existence of dark matter is reviewed: rotation curves of galaxies, weak
lensing measurements, hot gas in clusters, primordial nucleosynthesis and
microwave background experiments. In addition, a new line of research on Dark
Stars is presented, which suggests that the first stars to exist in the
universe were powered by dark matter heating rather than by fusion: the
observational possibilities of discovering dark matter in this way are
discussed.Comment: 14 pages, 7 figures, Conference Proceeding for "Dark Matter and Dark
Energy" in Lyon, France, July 200
Distribution of \u3ci\u3eStrongylium Crenatum\u3c/i\u3e (Coleoptera: Tenebrionidae) in the United States and First Record From Iowa
Strongylium crenatum Mäklin (Coleoptera: Tenebrionidae) is reported from Iowa for the first time. After discovering that Iowa represented a large range extension for this species, label data were collected to update its range. Numerous insect collections and references were checked and specimens representing 17 states were located
New State Records for \u3ci\u3ePerillus Strigipes\u3c/i\u3e (Heteroptera: Pentatomidae: Asopinae)
The stink bug Perillus strigipes is reported from Alabama, Iowa, Kansas, Louisiana, Maine, and Mississippi for the first time. This insect species has a wide distribution but generally is seldom collected
Generalized Cardassian Expansion: Models in Which the Universe is Flat, Matter Dominated, and Accelerating
The Cardassian universe is a proposed modification to the Friedmann Robertson
Walker (FRW) equation in which the universe is flat, matter dominated, and
accelerating. Here we generalize the original Cardassian proposal to include
additional variants on the FRW equation. Specific examples are presented.
In the ordinary FRW equation, the right hand side is a linear function of the
energy density, . Here, instead, the right hand side of the FRW
equation is a different function of the energy density, .
This function returns to ordinary FRW at early times, but modifies the
expansion at a late epoch of the universe. The only ingredients in this
universe are matter and radiation: in particular, there is {\it no} vacuum
contribution. Currently the modification of the FRW equation is such that the
universe accelerates. The universe can be flat and yet consist of only matter
and radiation, and still be compatible with observations. The energy density
required to close the universe is much smaller than in a standard cosmology, so
that matter can be sufficient to provide a flat geometry. The modifications may
arise, e.g., as a consequence of our observable universe living as a
3-dimensional brane in a higher dimensional universe. The Cardassian model
survives several observational tests, including the cosmic background
radiation, the age of the universe, the cluster baryon fraction, and structure
formation. As will be shown in future work, the predictions for observational
tests of the generalized Cardassian models can be very different from generic
quintessence models, whether the equation of state is constant or time
dependent.Comment: 5 pages, Conference Proceeding, Meeting on Sources and Detection of
Dark Matter and Dark Energy in the Universe, Marina del Rey, CA, February
200
Review of Statistics with Stata (Updated for Version 7)
The new book by Hamilton (2002) is reviewed. Copyright 2002 by Stata Corporation.
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