LX11811
Local pulsar exposed as source of energetic electrons and positrons
The surprising excesses of positrons and electrons recently detected
by the PAMELA and Fermi space experiments suggest that a source of such
cosmic rays must reside within our neighborhood of the Milky Way. Many
possibilities, including the annihilation or decay of dark matter
particles, have been proposed, although without any conclusive evidence.
In this Letter, we discuss how the unexpected "halo" of very-high-energy
gamma rays recently observed to surround the Geminga pulsar (a
rapidly-rotating neutron star) may be essential to resolving this
puzzle. We conclude that these gamma rays imply that a wind of
highly-energetic cosmic rays is escaping from Geminga, confirming the
presence of a powerful particle accelerator near the Earth. Cosmic rays
produced in Geminga's active past are, after a circuitous journey
through the Galaxy's tangled magnetic fields, likely the mysterious
"Positron Excess." This invites the exciting prospect that the long
sought identity of the origin of the highest-energy electrons and
positrons yet seen is now known.
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Excitons Can Couple Strongly to Plasmons in Individual Carbon Nanotubes
New theory and calculations show that excitons can couple to surface plasmons in individual semiconducting carbon nanotubes. The exciton-plasmon coupling strength can be tuned using a perpendicular electrostatic field. This new effect opens up new paths for the development of tunable nanophotonics device applications with carbon nanotubes.
One straightforward application is the exciton emission control from the individual nanotube by means of electrostatically driven exciton-plasmon coupling. This offers the advantage of less stringent fabrication requirements over the microcavity-controlled exciton emission (commonly used approach) since a photonic crystal microcavity is no longer required. Electrostatically controlled coupling of two spatially separated excitons to the same nanotube's plasmon mode would result in their entanglement, the phenomenon that paves the way for solid-state quantum information processing with carbon nanotubes. The theory developed also lays the foundation for understanding inter-tube energy transfer mechanisms in nanotube bundles and films, helping to reveal their potential for the development of high-yield optoelectronics applications with carbon nanotubes.
