11,172 research outputs found
Mixing of 1/2^- Octets under SU(3) Symmetry
We investigate the J^p=1/2^- baryons in the octets based on flavor SU(3)
symmetry. Since baryons with same quantum numbers can mix with each other, we
consider the mixing between two octets before their mixing with the singlet.
Most predicted decay widths are consistent with the experimental data, and
meanwhile we predict two possible mass ranges of the two octets.Comment: 8 latex page
Localized Asymmetric Atomic Matter Waves in Two-Component Bose-Einstein Condensates Coupled with Two Photon Microwave Field
We investigate localized atomic matter waves in two-component Bose-Einstein
condensates coupled by the two photon microwave field. Interestingly, the
oscillations of localized atomic matter waves will gradually decay and finally
become non-oscillating behavior even if existing coupling field. In particular,
atom numbers occupied in two different hyperfine spin states will appear
asymmetric occupations after some time evolution.Comment: 4 pages, 4 figure
Turning off the Lights: How Dark is Dark Matter?
We consider current observational constraints on the electromagnetic charge
of dark matter. The velocity dependence of the scattering cross-section through
the photon gives rise to qualitatively different constraints than standard dark
matter scattering through massive force carriers. In particular, recombination
epoch observations of dark matter density perturbations require that
, the ratio of the dark matter to electronic charge, is less than
for , rising to for .
Though naively one would expect that dark matter carrying a charge well below
this constraint could still give rise to large scattering in current direct
detection experiments, we show that charged dark matter particles that could be
detected with upcoming experiments are expected to be evacuated from the
Galactic disk by the Galactic magnetic fields and supernova shock waves, and
hence will not give rise to a signal. Thus dark matter with a small charge is
likely not a source of a signal in current or upcoming dark matter direct
detection experiments.Comment: 19 pages, 2 figures; v2 - figures fixed, references adde
Concatenating dynamical decoupling with decoherence-free subspaces for quantum computation
A scheme to implement a quantum computer subjected to decoherence and
governed by an untunable qubit-qubit interaction is presented. By concatenating
dynamical decoupling through bang-bang (BB) pulse with decoherence-free
subspaces (DFSs) encoding, we protect the quantum computer from
environment-induced decoherence that results in quantum information dissipating
into the environment. For the inherent qubit-qubit interaction that is
untunable in the quantum system, BB control plus DFSs encoding will eliminate
its undesired effect which spoils quantum information in qubits. We show how
this quantum system can be used to implement universal quantum computation.Comment: 6 pages,2 figures, 1 tabl
Maximally entangled mixed states of two atoms trapped inside an optical cavity
In some off-resonant cases, the reduced density matrix of two atoms
symmetrically coupled with an optical cavity can very approximately approach to
maximally entangled mixed states or maximal Bell violation mixed states in
their evolution. The influence of phase decoherence on the generation of
maximally entangled mixed state is also discussed.
PACS numbers: 03.67.-a, 03.65.UdComment: 7 pages, 4 figures, Latex, have a major revision of content
A Higgs Quadruplet for Type III Seesaw and Implications for and Conversion
In Type III seesaw model the heavy neutrinos are contained in leptonic
triplet representations. The Yukawa couplings of the triplet fermion and the
left-handed neutrinos with the doublet Higgs field produce the Dirac mass
terms. Together with the Majorana masses for the leptonic triplets, the light
neutrinos obtain non-zero seesaw masses. We point out that it is also possible
to have a quadruplet Higgs field to produce the Dirac mass terms to facilitate
the seesaw mechanism. The vacuum expectation value of the quadruplet Higgs is
constrained to be small by electroweak precision data. Therefore the Yukawa
couplings of a quadruplet can be much larger than those for a doublet. We also
find that unlike the usual Type III seesaw model where at least two copies of
leptonic triplets are needed, with both doublet and quadruplet Higgs
representations, just one leptonic triplet is possible to have a
phenomenologically acceptable model because light neutrino masses can receive
sizable contributions at both tree and one loop levels. Large Yukawa couplings
of the quadruplet can induce observable effects for lepton flavor violating
processes and conversion. Implications of the
recent limit from MEG and also limit on conversion
on Au are also given. Some interesting collider signatures for the doubly
charged Higgs boson in the quadruplet are discussed.Comment: Latex 11 pages, 1 figure. A few references adde
Flight Mechanics and Control of Escape Manoeuvres in Hummingbirds. I. Flight Kinematics
Hummingbirds are nature’s masters of aerobatic manoeuvres. Previous research shows that hummingbirds and insects converged evolutionarily upon similar aerodynamic mechanisms and kinematics in hovering. Herein, we use three-dimensional kinematic data to begin to test for similar convergence of kinematics used for escape flight and to explore the effects of body size upon manoeuvring. We studied four hummingbird species in North America including two large species (magnificent hummingbird, Eugenes fulgens, 7.8 g, and blue-throated hummingbird, Lampornis clemenciae, 8.0 g) and two smaller species (broad-billed hummingbird, Cynanthus latirostris, 3.4 g, and black-chinned hummingbirds Archilochus alexandri, 3.1 g). Starting from a steady hover, hummingbirds consistently manoeuvred away from perceived threats using a drastic escape response that featured body pitch and roll rotations coupled with a large linear acceleration. Hummingbirds changed their flapping frequency and wing trajectory in all three degrees of freedom on a stroke-by-stroke basis, likely causing rapid and significant alteration of the magnitude and direction of aerodynamic forces. Thus it appears that the flight control of hummingbirds does not obey the ‘helicopter model’ that is valid for similar escape manoeuvres in fruit flies. Except for broad-billed hummingbirds, the hummingbirds had faster reaction times than those reported for visual feedback control in insects. The two larger hummingbird species performed pitch rotations and global-yaw turns with considerably larger magnitude than the smaller species, but roll rates and cumulative roll angles were similar among the four species
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