19,557 research outputs found
Can Heavy WIMPs Be Captured by the Earth?
If weakly interacting massive particles (WIMPs) in bound solar orbits are
systematically driven into the Sun by solar-system resonances (as Farinella et
al. have shown is the case for many Earth-crossing asteroids), then the capture
of high-mass WIMPs by the Earth would be affected dramatically because
high-mass WIMPs are captured primarily from bound orbits. WIMP capture would be
eliminated for M_x>630 GeV and would be highly suppressed for M_x>~150 GeV.
Annihilation of captured WIMPs and anti-WIMPs is expected to give rise to
neutrinos coming from the Earth's center. The absence of such a neutrino signal
has been used to place limits on WIMP parameters. At present, one does not know
if typical WIMP orbits are in fact affected by these resonances. Until this
question is investigated and resolved, one must (conservatively) assume that
they are. Hence, limits on high-mass WIMP parameters are significantly weaker
than previously believed.Comment: 8 pages + 1 figure. Submitted to Ap
Longitudinal Oscillations in Bounded Magnetoplasmas
Fine structure in absorption due to Buchsbaum-Hasegawa modes is observed over a wider range of magnetic fields than previously reported (omegac/omega = 0.5−0.985). The basic theory is satisfactory only near the cyclotron harmonic
Central America's Macroeconomic Environment and the Role of the Investment Climate under Free Trade
Central America's economic performance in recent years has benefited from improved macroeconomic management, a favorable external environment, as well as rising investor confidence since the region has pursued greater access to global markets, particularly with the signing of DR-CAFTA in 2004. Nonetheless, while important reforms have been made, at the sectoral level, much remains to be done. The context of a less favorable global environment underlines the need to improve competiveness and enhance productivity. An improved investment climate would contribute to both and help to unleash the full potential of DR-CAFTA.Macroeconomic performance; investment climate; Guatemala; El Salvador; Nicaragua; Hounduras; Costa Rica; Panama
Nonlinear programming without a penalty function or a filter
A new method is introduced for solving equality constrained nonlinear optimization problems. This method does not use a penalty function, nor a barrier or a filter, and yet can be proved to be globally convergent to first-order stationary points. It uses different trust-regions to cope with the nonlinearities of the objective function and the constraints, and allows inexact SQP steps that do not lie exactly in the nullspace of the local Jacobian. Preliminary numerical experiments on CUTEr problems indicate that the method performs well
Zero field spin polarization in a 2D paramagnetic resonant tunneling diode
We study I-V characteristics of an all-II-VI semiconductor resonant tunneling
diode with dilute magnetic impurities in the quantum well layer. Bound magnetic
polaron states form in the vicinity of potential fluctuations at the well
interface while tunneling electrons traverse these interface quantum dots. The
resulting microscopic magnetic order lifts the degeneracy of the resonant
tunneling states. Although there is no macroscopic magnetization, the resulting
resonant tunneling current is highly spin polarized at zero magnetic field due
to the zero field splitting. Detailed modeling demonstrates that the local spin
polarization efficiency exceeds 90% without an external magnetic field.Comment: 7 pages, 10 figures (including supplementary information
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