6,418 research outputs found
Electron beams of cylindrically symmetric spin polarization
Cylindrically symmetric electron beams in spin polarization are reported for
the first time. They are shown to be the eigen states of total angular momentum
in the direction. But they are neither the eigen states of spin nor the
eigen states of orbital angular momentum in that direction.Comment: 10 pages and 2 figure
Density and Spin Linear Response of Atomic Fermi Superfluids with Population Imbalance in BCS-BEC Crossover
We present a theoretical study of the density and spin (representing the two
components) linear response of Fermi superfluids with tunable attractive
interactions and population imbalance. In both linear response theories, we
find that the fluctuations of the order parameter must be treated on equal
footing with the gauge transformations associated with the symmetries of the
Hamiltonian so that important constraints including various sum rules can be
satisfied. Both theories can be applied to the whole BCS-Bose-Einstein
condensation crossover. The spin linear responses are qualitatively different
with and without population imbalance because collective-mode effects from the
fluctuations of the order parameter survive in the presence of population
imbalance, even though the associated symmetry is not broken by the order
parameter. Since a polarized superfluid becomes unstable at low temperatures in
the weak and intermediate coupling regimes, we found that the density and spin
susceptibilities diverge as the system approaches the unstable regime, but the
emergence of phase separation preempts the divergence.Comment: 15 pages, 5 figure
A Non-Mainstream Viewpoint on Apparent Superluminal Phenomena in AGN Jet
The group velocity of light in material around the AGN jet is acquiescently
one (c as a unit), but this is only a hypothesis. Here, we re-derive apparent
superluminal and Doppler formulas for the general case (it is assumed that the
group velocity of light in the uniform and isotropic medium around a jet (a
beaming model) is not necessarily equal to one, e.g., Araudo et al. (2010)
thought that there may be dense clouds around AGN jet base), and show that the
group velocity of light close to one could seriously affect apparent
superluminal phenomena and Doppler effect in the AGN jet (when the viewing
angle and Lorentz factor take some appropriate values).Comment: 4 pages, 2 figures, new version accepted for publication in Journal
of Astrophysics and Astronom
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