1,728 research outputs found
Bound-state dark matter with Majorana neutrinos
We propose a simple scenario in which dark matter (DM) emerges as a stable
neutral hadronic thermal relics, its stability following from an exact
symmetry. Neutrinos pick up radiatively induced
Majorana masses from the exchange of colored DM constituents. There is a common
origin for both dark matter and neutrino mass, with a lower bound for
neutrinoless double beta decay. Direct DM searches at nuclear recoil
experiments will test the proposal, which may also lead to other
phenomenological signals at future hadron collider and lepton flavour violation
experiments.Comment: 9 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1803.0852
Decaying neutralino dark matter in anomalous models
In supersymmetric models extended with an anomalous different
R-parity violating couplings can yield an unstable neutralino. We show that in
this context astrophysical and cosmological constraints on neutralino decaying
dark matter forbid bilinear R-parity breaking neutralino decays and lead to a
class of purely trilinear R-parity violating scenarios in which the neutralino
is stable on cosmological scales. We have found that among the resulting models
some of them become suitable to explain the observed anomalies in cosmic-ray
electron/positron fluxes.Comment: 19 pages, 3 figures. References added, typos corrected, accepted
version in Phys Rev
Determination of nanogram microparticles from explosives after real open-air explosions by confocal Raman microscopy
Explosives are increasingly being used for terrorist attacks to cause devastating explosions. The detection of their post-blast residues after an explosion is a high challenge, which has been barely investigated, particularly using spectroscopic techniques. In this research, a novel methodology using confocal Raman microscopy has been developed for the analysis of post-blast residues from ten open-air explosions caused by ten different explosives (TNT, RDX, PETN, TATP, HMTD, dynamite, black powder, ANFO, chloratite, and ammonal) commonly used in improvised explosive devices. The methodology for the determination of post-blast particles from explosives consisted of examining the samples surfaces with both the naked eye, first, and microscopically (10x and 50x), immediately afterward; and finally, analysing the selected residues by confocal Raman spectroscopy in order to identify the post-blast particles from explosives. Interestingly, confocal Raman microscopy has demonstrated to be highly suitable to rapidly, selectively and non-invasively analyse post-blast microscopic particles from explosives up to the nanogram range
Resonant Hawking radiation in Bose-Einstein condensates
We study double-barrier interfaces separating regions of asymptotically
subsonic and supersonic flow of Bose condensed atoms. These setups contain at
least one black hole sonic horizon from which the analog of Hawking radiation
should be generated and emitted against the flow in the subsonic region.
Multiple coherent scattering by the double-barrier structure strongly modulates
the transmission probability of phonons, rendering it very sensitive to their
frequency. As a result, resonant tunneling occurs with high probability within
a few narrow frequency intervals. This gives rise to highly non-thermal spectra
with sharp peaks. We find that these peaks are mostly associated to decaying
resonances and only occasionally to dynamical instabilities. Even at achievable
nonzero temperatures, the radiation peaks can be dominated by the spontaneous
emission, i.e. enhanced zero-point fluctuations, and not, as often in analog
models, by stimulated emission.Comment: 20 pages, 9 figures, revised versio
Oscillatory decay of a two-component Bose-Einstein condensate
We study the decay of a two-component Bose-Einstein condensate with negative
effective interaction energy. With a decreasing atom number due to losses, the
atom-atom interaction becomes less important and the system undergoes a
transition from a bistable Josephson regime to the monostable Rabi regime,
displaying oscillations in phase and number. We study the equations of motion
and derive an analytical expression for the oscillation amplitude. A quantum
trajectory simulation reveals that the classical description fails for low
emission rates, as expected from analytical considerations. Observation of the
proposed effect will provide evidence for negative effective interaction.Comment: 4 pages, 3 figue
Voltage rectification by a SQUID ratchet
We argue that the phase across an asymmetric dc SQUID threaded by a magnetic
flux can experience an effective ratchet (periodic and asymmetric) potential.
Under an external ac current, a rocking ratchet mechanism operates whereby one
sign of the time derivative of the phase is favored. We show that there exists
a range of parameters in which a fixed sign (and, in a narrower range, even a
fixed value) of the average voltage across the ring occurs, regardless of the
sign of the external current dc component.Comment: 4 pages, 4 EPS figures, uses psfig.sty. Revised version, to appear in
Physical Review Letters (26 August 1996
Dark Matter in the Universe: Evidence, Candidates and Searches
Contribution from the students of the 4th CERNCLAF School of High-Energy Physics who participated in the Discussion Session addressing the issues of dark matter in the Universe
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