48,564 research outputs found
Charged lepton mixing and oscillations from neutrino mixing in the early Universe
Charged lepton mixing as a consequence of neutrino mixing is studied for two
generations in the temperature regime in the
early Universe. We state the general criteria for charged lepton mixing,
critically reexamine aspects of neutrino equilibration and provide arguments to
suggest that neutrinos may equilibrate as mass eigenstates in the temperature
regime \emph{prior} to flavor equalization. We assume this to be the case, and
that neutrino mass eigenstates are in equilibrium with different chemical
potentials. Charged lepton self-energies are obtained to leading order in the
electromagnetic and weak interactions. The upper bounds on the neutrino
asymmetry parameters from CMB and BBN without oscillations, combined with the
fit to the solar and KamLAND data for the neutrino mixing angle, suggest that
for the two generation case there is resonant \emph{charged lepton} mixing in
the temperature range . In this range the charged lepton
oscillation frequency is of the same order as the electromagnetic damping rate.Comment: 17 pages, 2 figs, same results with more discussions on quantum Zeno
effect. To appear in Astroparticle Physic
Effect of epitaxial strain on ferroelectric polarization in multiferroic BiFeO3 films
Multiferroic BiFeO3 epitaxial films with thickness ranging from 40 nm to 960
nm were grown by pulsed laser deposition on SrTiO3 (001) substrates with SrRuO3
bottom electrodes. X-ray characterization shows that the structure evolves from
angularly-distorted tetragonal with c/a ~ 1.04 to more bulk-like distorted
rhombohedral (c/a ~ 1.01) as the strain relaxes with increasing thickness.
Despite this significant structural evolution, the ferroelectric polarization
along the body diagonal of the distorted pseudo-cubic unit cells, as calculated
from measurements along the normal direction, barely changes.Comment: Legend in Fig.3 corrected and et
Supersymmetric reduced models with a symmetry based on Filippov algebra
Generalizations of the reduced model of super Yang-Mills theory obtained by
replacing the Lie algebra structure to Filippov -algebra structures are
studied. Conditions for the reduced model actions to be supersymmetric are
examined. These models are related with what we call \{cal N}_{min}=2 super
-brane actions.Comment: v3: In the previous versions we overlooked that Eq.(3.9) holds more
generally, and missed some supersymmetric actions. Those are now included and
modifications including a slight change in the title were made accordingly.
1+18 page
Spinor Bose Condensates in Optical Traps
In an optical trap, the ground state of spin-1 Bosons such as Na,
K, and Rb can be either a ferromagnetic or a "polar" state,
depending on the scattering lengths in different angular momentum channel. The
collective modes of these states have very different spin character and spatial
distributions. While ordinary vortices are stable in the polar state, only
those with unit circulation are stable in the ferromagnetic state. The
ferromagnetic state also has coreless (or Skyrmion) vortices like those of
superfluid He-A. Current estimates of scattering lengths suggest that the
ground states of Na and Rb condensate are a polar state and a
ferromagnetic state respectively.Comment: 11 pages, no figures. email : [email protected]
Noncommutative D-Brane in Non-Constant NS-NS B Field Background
We show that when the field strength H of the NS-NS B field does not vanish,
the coordinates X and momenta P of an open string endpoints satisfy a set of
mixed commutation relations among themselves. Identifying X and P with the
coordinates and derivatives of the D-brane world volume, we find a new type of
noncommutative spaces which is very different from those associated with a
constant B field background.Comment: 11 pages, Latex, minor modification
Improved Spin Dynamics Simulations of Magnetic Excitations
Using Suzuki-Trotter decompositions of exponential operators we describe new
algorithms for the numerical integration of the equations of motion for
classical spin systems. These techniques conserve spin length exactly and, in
special cases, also conserve the energy and maintain time reversibility. We
investigate integration schemes of up to eighth order and show that these new
algorithms can be used with much larger time steps than a well established
predictor-corrector method. These methods may lead to a substantial speedup of
spin dynamics simulations, however, the choice of which order method to use is
not always straightforward.Comment: J. Mod. Phys. C (in press
Efficient out-coupling and beaming of Tamm optical states via surface plasmon polariton excitation
We present evidence of optical Tamm states to surface plasmon polariton (SPP) coupling. We experimentally demonstrate that for a Bragg stack with a thin metal layer on the surface, hybrid Tamm-SPP modes may be excited when a grating on the air-metal interface is introduced. Out-coupling via the grating to free space propagation is shown to enhance the transmission as well as the directionality and polarization selection for the transmitted beam. We suggest that this system will be useful on those devices, where a metallic electrical contact as well as beaming and polarization control is needed
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