10,882 research outputs found
Displaced Higgs production in type III seesaw
We point out that the type III seesaw mechanism introducing fermion triplets
predicts peculiar Higgs boson signatures of displaced vertices with two b jets
and one or two charged particles which can be cleanly identified. In a
supersymmetric theory, the scalar partner of the fermion triplet contains a
neutral dark matter candidate which is almost degenerate with its charged
components. A Higgs boson can be produced together with such a dark matter
triplet in the cascade decay chain of a strongly produced squark or gluino.
When the next lightest supersymmetric particle (NLSP) is bino/wino-like, there
appears a Higgs boson associated with two charged tracks of a charged lepton
and a heavy charged scalar at a displacement larger than about 1 mm. The
corresponding production cross-section is about 0.5 fb for the squark/gluino
mass of 1 TeV. In the case of the stau NLSP, it decays mainly to a Higgs boson
and a heavy charged scalar whose decay length is larger than 0.1 mm for the
stau NLSP mixing with the left-handed stau smaller than 0.3. As this process
can have a large cascade production pb for the squark/gluino mass
TeV, one may be able to probe it at the early stage of the LHC
experiment.Comment: 10 pages, 5 figure
Auxiliary field formalism for dilute fermionic atom gases with tunable interactions
We develop the auxiliary field formalism corresponding to a dilute system of
spin-1/2 fermions. This theory represents the Fermi counterpart of the BEC
theory developed recently by F. Cooper et al. [Phys. Rev. Lett. 105, 240402
(2010)] to describe a dilute gas of Bose particles. Assuming tunable
interactions, this formalism is appropriate for the study of the crossover from
the regime of Bardeen-Cooper-Schriffer (BCS) pairing to the regime of
Bose-Einstein condensation (BEC) in ultracold fermionic atom gases. We show
that when applied to the Fermi case at zero temperature, the leading-order
auxiliary field (LOAF) approximation gives the same equations as those obtained
in the standard BCS variational picture. At finite temperature, LOAF leads to
the theory discussed by by Sa de Melo, Randeria, and Engelbrecht [Phys. Rev.
Lett. 71, 3202(1993); Phys. Rev. B 55, 15153(1997)]. As such, LOAF provides a
unified framework to study the interacting Fermi gas. The mean-field results
discussed here can be systematically improved upon by calculating the
one-particle irreducible (1-PI) action corrections, order by order.Comment: 12 pages, 5 figure
Strain induced half-metal to semiconductor transition in GdN
We have investigated the electronic structure and magnetic properties of GdN
as a function of unit cell volume. Based on the first-principles calculations
of GdN, we observe that there is a transformation in conduction properties
associated with the volume increase: first from halfmetallic to semi-metallic,
then ultimately to semiconducting. We show that applying stress can alter the
carrier concentration as well as mobility of the holes and electrons in the
majority spin channel. In addition, we found that the exchange parameters
depend strongly on lattice constant, thus the Curie temperature of this system
can be enhanced by applying stress or doping impurities.Comment: 9 pages, 3 figure
On Lattice Computations of K+ --> pi+ pi0 Decay at m_K =2m_pi
We use one-loop chiral perturbation theory to compare potential lattice
computations of the K+ --> pi+ pi0 decay amplitude at m_K=2m_pi with the
experimental value. We find that the combined one-loop effect due to this
unphysical pion to kaon mass ratio and typical finite volume effects is still
of order minus 20-30%, and appears to dominate the effects from quenching.Comment: 4 pages, revte
Coercive Field and Magnetization Deficit in Ga(1-x)Mn(x)As Epilayers
We have studied the field dependence of the magnetization in epilayers of the
diluted magnetic semiconductor Ga(1-x)Mn(x)As for 0.0135 < x < 0.083.
Measurements of the low temperature magnetization in fields up to 3 T show a
significant deficit in the total moment below that expected for full saturation
of all the Mn spins. These results suggest that the spin state of the
non-ferromagnetic Mn spins is energetically well separated from the
ferromagnetism of the bulk of the spins. We have also studied the coercive
field (Hc) as a function of temperature and Mn concentration, finding that Hc
decreases with increasing Mn concentration as predicted theoretically.Comment: 15 total pages -- 5 text, 1 table, 4 figues. Accepted for publication
in MMM 2002 conference proceedings (APL
Hole effective mass in remote doped Si/Si1âxGex quantum wells with 0.05x0.3
The effective masses in remote doped Si/Si1âxGex hole quantum wells with 0.05<=x<=0.3, have been determined from the temperature dependence of the Shubnikovâde Haas oscillations. The values are lower than previously observed by other workers, but still somewhat higher than the theoretical Gamma-point values for the ground-state heavy hole subband. The differences are attributed to finite carrier sheet densities and can be satisfactorily accounted for by nonparabolicity corrections
Unified theory for Goos-H\"{a}nchen and Imbert-Fedorov effects
A unified theory is advanced to describe both the lateral Goos-H\"{a}nchen
(GH) effect and the transverse Imbert-Fedorov (IF) effect, through representing
the vector angular spectrum of a 3-dimensional light beam in terms of a 2-form
angular spectrum consisting of its 2 orthogonal polarized components. From this
theory, the quantization characteristics of the GH and IF displacements are
obtained, and the Artmann formula for the GH displacement is derived. It is
found that the eigenstates of the GH displacement are the 2 orthogonal linear
polarizations in this 2-form representation, and the eigenstates of the IF
displacement are the 2 orthogonal circular polarizations. The theoretical
predictions are found to be in agreement with recent experimental results.Comment: 15 pages, 3 figure
Correlation between 3:2 QPO pairs and Jets in Black Hole X-ray Binaries
We argue, following our earlier works (the "CEBZMC model"), that the
phenomenon of twin peak high frequency quasi-periodic oscillations (QPOs)
observed in black hole X-ray binaries is caused by magnetic coupling (MC)
between accretion disk and black hole (BH). Due to MC, two bright spots occur
at two separate radial locations r_{in} and r_{out} at the disk surface,
energized by a kind of the Blandford-Znajek mechanism (BZ). We assume,
following the Kluzniak-Abramowicz QPO resonance model, that Keplerian
frequencies at these two locations are in the 3:2 ratio. With this assumption,
we estimate the BH spins in several sources, including GRO J1655-40, GRS
1915+105, XTE J1550-564, H1743-322 and Sgr A*. We give an interpretation of the
"jet line" in the hardness-intensity plane discussing the parameter space
consisting of the BH spin and the power-law index for the variation of the
large-scale magnetic field in the disk. Furthermore, we propose a new scenario
for the spectral state transitions in BH X-ray binaries based on fluctuation in
densities of accreting plasma from a companion star.Comment: 17 pages, 6 figures, accepted by AP
Hole effective mass in remote doped Si/Si1âxGex quantum wells with 0.05x0.3
The effective masses in remote doped Si/Si1âxGex hole quantum wells with 0.05<=x<=0.3, have been determined from the temperature dependence of the Shubnikovâde Haas oscillations. The values are lower than previously observed by other workers, but still somewhat higher than the theoretical Gamma-point values for the ground-state heavy hole subband. The differences are attributed to finite carrier sheet densities and can be satisfactorily accounted for by nonparabolicity corrections
Evidence of ratchet effect in nanowires of a conducting polymer
Ratchet effect, observed in many systems starting from living organism to
artificially designed device, is a manifestation of motion in asymmetric
potential. Here we report results of a conductivity study of Polypyrrole
nanowires, which have been prepared by a simple method to generate a variation
of doping concentration along the length. This variation gives rise to an
asymmetric potential profile that hinders the symmetry of the hopping process
of charges and hence the value of measured resistance of these nanowires become
sensitive to the direction of current flow. The asymmetry in resistance was
found to increase with decreasing nanowire diameter and increasing temperature.
The observed phenomena could be explained with the assumption that the spatial
extension of localized state involved in hopping process reduces as the doping
concentration reduces along the length of the nanowires.Comment: Revtex, two column, 4 pages, 10 figure
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