APS Physics Tip Sheet – Apr 22, 2014
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Sterile Neutrino as Dark-Matter Candidate
A dark matter particle in the form of a so-called sterile neutrino could explain the recent detection of an x-ray emission line from galaxy clusters.
Recent astronomical observations of the Andromeda Galaxy and the Perseus Cluster have revealed an x-ray emission line whose origin cannot be explained. A researcher from UC Irvine has now suggested that such x rays could be generated through the decay of dark matter particles in the form of sterile neutrinos—hypothetical neutrinos that do not interact via any of the fundamental interactions except gravity. The researcher calculates that the decay of sterile neutrinos would produce x rays exactly at the observed wavelength. Further, he shows that a cosmological model based on this sterile-neutrino dark-matter particle would solve two key problems faced by the currently most popular dark-matter models: correctly predicting both the number of Milky Way satellite galaxies and their central densities.
* Kevork N Abazajian (contact author), “Resonantly-Produced 7 keV Sterile Neutrino Dark Matter Models and the Properties of Milky Way Satellites,” Physical Review Letters (expected publication date: Apr 24)
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Amber Does Not Act Its Age
110-million-year-old amber samples surprisingly retain the same thermodynamic properties as much younger glasses.
Amber is a unique example of a glass because it has “hyperaged,” that is, it has undergone thermodynamic stabilization for millions of years—a process that is impossible to replicate in a lab. This allows researchers to study how the properties of a glass change with age. A team of researchers from Spain has measured the specific heat and other thermodynamic properties of a 110-million-year-old amber sample, finding that such features are identical to those of younger samples. The result implies that the thermodynamic properties remain fossilized in the glass—much like a trapped insect—and are surprisingly unchanged by 110 million years of aging.
* T Pérez-Castañeda, RJ Jiménez-Riobóo, Miguel A Ramos (contact author), “Two-level systems and boson peak in 110-million-year-aged amber glass,” Physical Review Letters (published Apr 22)
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Stopping Light in a Waveguide
A new proposal suggests light could be stopped in a compact, solid-state device working under ambient conditions.
Researchers have recently demonstrated a variety of methods to stop light—a phenomenon that could be used, for instance, to process information in an optical network. But most available techniques are based on complex setups using ultracold gases and can only stop light in a very narrow band of frequencies. A new method, theorized by a group at Imperial College, in London, could decelerate light pulses down to 20 meters per second inside a waveguide made of a silicon core surrounded by a metal layer. The scheme, which could lead to practical devices working under ambient conditions, could stop light for a time long enough for applications like fast optical switches, nanolasers, and solar cells.
* Kosmas L Tsakmakidis (contact author) et al, “Completely Stopped and Dispersionless Light in Plasmonic Waveguides,” Physical Review Letters (expected publication date: Apr 25)
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An Undulator Made of Microwaves
Researchers at SLAC National Accelerator Laboratory have used a microwave cavity to build an undulator—a device that causes electrons to jiggle and emit a beam of intense and coherent x rays. Instead of using the field of fixed magnets as in conventional undulators, the scheme exploits the magnetic and electric fields of intense microwaves in a cavity. The new type of undulator may outperform conventional ones in the generation of x-ray radiation at very short wavelengths for high-resolution imaging and crystallography applications.
* S Tantawi, Muhammad Shumail (contact author) et al, “Experimental demonstration of a tunable microwave undulator,” Physical Review Letters (expected publication date: Apr 23)
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Matteo Rini, PhD
Deputy Editor, Physics
