Kaluza-Klein Dark Matter and the Positron Excess

The excess of cosmic positrons observed by the HEAT experiment may be the result of Kaluza-Klein dark matter annihilating in the galactic halo. Kaluza-Klein dark matter annihilates dominantly into charged leptons that yield a large number and hard spectrum of positrons per annihilation. Given a Kaluza-Klein dark matter particle with a mass in the range of 300-400 GeV, no exceptional substructure or clumping is needed in the local distribution of dark matter to generate a positron flux that explains the HEAT observations. This is in contrast to supersymmetric dark matter that requires unnaturally large amounts of dark substructure to produce the observed positron excess. Future astrophysical and collider tests are outlined that will confirm or rule out this explanation of the HEAT data.Comment: 5 pages, 3 figures, REVTeX

On a Solar Origin for the Cosmogenic Nuclide Event of 775 A.D.

We explore requirements for a solar particle event (SPE) and flare capable of producing the cosmogenic nuclide event of 775 A.D., and review solar circumstances at that time. A solar source for 775 would require a greater than 1 GV spectrum approximately 45 times stronger than that of the intense high-energy SPE of 1956 February 23. This implies a greater than 30 MeV proton fluence (F(sub 30)) of approximately 8 10(exp 10) proton cm(exp 2), approximately 10 times larger than that of the strongest 3 month interval of SPE activity in the modern era. This inferred F(sub 30) value for the 775 SPE is inconsistent with the occurrence probability distribution for greater than 30 MeV solar proton events. The best guess value for the soft X-ray classification (total energy) of an associated flare is approximately X230 (approximately 9 10(exp 33) erg). For comparison, the flares on 2003 November 4 and 1859 September 1 had observed/inferred values of approximately X35 (approximately 10(exp 33) erg) and approximately X45 (approximately 2 10(exp 33) erg), respectively. The estimated size of the source active region for a approximately 10(exp 34) erg flare is approximately 2.5 times that of the largest region yet recorded. The 775 event occurred during a period of relatively low solar activity, with a peak smoothed amplitude about half that of the second half of the 20th century. The approximately 1945-1995 interval, the most active of the last approximately 2000 yr, failed to witness a SPE comparable to that required for the proposed solar event in 775. These considerations challenge a recent suggestion that the 775 event is likely of solar origin

Soybean Cyst Nematode Reduces Soybean Yield Without Causing Obvious Aboveground Symptoms

Field experiments were conducted at locations in northern and southern Illinois, central Iowa, and central Missouri from 1997 to 1999 to investigate the effects of Heterodera glycines on soybean growth, development, and yield. A wide range of infestation levels was present at all locations. Two locally adapted cultivars, one resistant to H. glycines, were grown at each location. Cultivars were planted in alternating four-row strips with 76 cm between rows. For each cultivar, 20 1-m-long single-row plots were sampled every 2 weeks starting 4 weeks after planting. Infection by H. glycines reduced plant height and leaf and stem weight on the resistant cultivars in the first 12 weeks after planting, and delayed pod and seed development 12 to 14 weeks after planting. Biomass accumulation was not reduced on the susceptible cultivars until 10 weeks after planting; reduction in pod and seed development occurred throughout the reproductive stages. Susceptible cultivars produced significantly lower yields than resistant cultivars, but the yield reductions were not accompanied by visually detectable symptoms

Trapping of strangelets in the geomagnetic field

Strangelets coming from the interstellar medium (ISM) are an interesting target to experiments searching for evidence of this hypothetic state of hadronic matter. We entertain the possibility of a {\it trapped} strangelet population, quite analogous to ordinary nuclei and electron belts. For a population of strangelets to be trapped by the geomagnetic field, these incoming particles would have to fulfill certain conditions, namely having magnetic rigidities above the geomagnetic cutoff and below a certain threshold for adiabatic motion to hold. We show in this work that, for fully ionized strangelets, there is a narrow window for stable trapping. An estimate of the stationary population is presented and the dominant loss mechanisms discussed. It is shown that the population would be substantially enhanced with respect to the ISM flux (up to two orders of magnitude) due to quasi-stable trapping.Comment: 10 pp., 5 figure

Observation of Energetic Trapped Oxygen Ions in the Inner Magnetosphere

We report on a series of measurements of 5-30 Me V /nuc oxygen ions made with trackdetector stacks on Cosmos satellites. We find that the angular distributions during solar energetic particle events are isotropic, while solar-quiet times show highly anisotropic distributions suggestive of a trapped particle component. Detailed Monte Carlo simulations confirm this interpretation and allow us to separate the trapped and cosmic ray contributions to the quiet-time fluxes. Our data appear fully consistent with trapping of anomalous cosmic ray ions as the source of the trapped particles but inconsistent with radial diffusion from the outer radiation zone

Source regions of major solar energetic particle events

Abstract We examine the source regions of the largest prompt solar energetic particle (SEP) events (J proton [>10 MeV] >100 pr/cm 2 /s/sr) occurring between 1992 and 2002. We find that the 25 such events originated in a broad spectrum of solar regions, ranging from large complex active regions with delta sunspot groups (e.g., 30 October 1992) to a very weak active region in which the major feature was a large filament that erupted to produce the SEP event (12 September 2000). Most source regions are less than two rotation old. In terms of recent work to identify two types of large SEP events on the basis of composition, spectra, and charge state, we find that large complex active regions can give rise to both types, whereas simple and magnetically weak regions are preferentially linked to one type

Evidence for Remnant Flare Suprathermals In The Source Population of Solar Energetic Particles In The 2000 Bastille Day Event

The energy spectra of Fe in the very large solar energetic particle (SEP) event of 2000 July 14 are strikingly different from those of lighter species. We show that this difference can be explained by shock acceleration from a two-component source population, comprising solar wind suprathermals and a small (∼5%) admixture of remnant flare particles, as previously proposed to explain enhanced ^3He/^4He in some gradual SEP events. Flare remnants can also account for several previously unexplained features of high-energy solar heavy ions as well as important aspects of SEP event-to-event variability. These results offer a new perspective on the enduring controversy over the relative roles of flares and coronal mass ejections (CMEs) in producing SEPs. Flare activity clearly makes a unique and critical contribution to the source population. But the predominate accelerator in large gradual SEP events is the CME-driven shock, and many spectral, compositional, and charge state characteristics of highenergy heavy ions can be understood without invoking other acceleration mechanisms