43,227 research outputs found
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
Spin diffusion of correlated two-spin states in a dielectric crystal
Reciprocal space measurements of spin diffusion in a single crystal of
calcium fluoride (CaF) have been extended to dipolar ordered states. The
experimental results for the component of the spin diffusion parallel with the
external field are cm/s for the
[001] direction and cm/s for the
[111] direction. The diffusion rates for dipolar order are significantly faster
than those for Zeeman order and are considerably faster than predicted by
simple theoretical models. It is suggested that constructive interference in
the transport of the two spin state is responsible for this enhancement. As
expected the anisotropy in the diffusion rates is observed to be significantly
less for dipolar order compared to the Zeeman case.Comment: 4 pages, 2 figures. Resubmitted to PRL - new figure added /
discussion expande
Fault-tolerant linear optics quantum computation by error-detecting quantum state transfer
A scheme for linear optical implementation of fault-tolerant quantum
computation is proposed, which is based on an error-detecting code. Each
computational step is mediated by transfer of quantum information into an
ancilla system embedding error-detection capability. Photons are assumed to be
subjected to both photon loss and depolarization, and the threshold region of
their strengths for scalable quantum computation is obtained, together with the
amount of physical resources consumed. Compared to currently known results, the
present scheme reduces the resource requirement, while yielding a comparable
threshold region.Comment: 9 pages, 7 figure
Lineal Trails of D2-D2bar Superstrings
We study the superstrings suspended between a D2- and an anti-D2-brane. We
quantize the string in the presence of some general configuration of gauge
fields over the (anti-)D-brane world volumes. The interstring can move only in
a specific direction that is normal to the difference of the electric fields of
each (anti-)D-branes. Especially when the electric fields are the same, the
interstring cannot move. We obtain the condition for the tachyons to disappear
from the spectrum.Comment: 15 pages with 4 figures, referenced added, Sec. 5 on the spectrum
made cleare
Super Jackstraws and Super Waterwheels
We construct various new BPS states of D-branes preserving 8 supersymmetries.
These include super Jackstraws (a bunch of scattered D- or (p,q)-strings
preserving supersymmetries), and super waterwheels (a number of D2-branes
intersecting at generic angles on parallel lines while preserving
supersymmetries). Super D-Jackstraws are scattered in various dimensions but
are dynamical with all their intersections following a common null direction.
Meanwhile, super (p,q)-Jackstraws form a planar static configuration. We show
that the SO(2) subgroup of SL(2,R), the group of classical S-duality
transformations in IIB theory, can be used to generate this latter
configuration of variously charged (p,q)-strings intersecting at various
angles. The waterwheel configuration of D2-branes preserves 8 supersymmetries
as long as the `critical' Born-Infeld electric fields are along the common
direction.Comment: 23 pages, 10 figure
Analytic continuation of the Hurwitz Zeta Function with physical application
A new formula relating the analytic continuation of the Hurwitz zeta function
to the Euler gamma function and a polylogarithmic function is presented. In
particular, the values of the first derivative of the real part of the analytic
continuation of the Hurwitz zeta function for even negative integers and the
imaginary one for odd negative integers are explicitly given. The result can be
of interest both on mathematical and physical side, because we are able to
apply our new formulas in the context of the Spectral Zeta Function
regularization, computing the exact pair production rate per space-time unit of
massive Dirac particles interacting with a purely electric background field.Comment: Replaced version, minor changes. 9 pages, to be published in J. Math.
Phy
Weak boson fusion production of supersymmetric particles at the LHC
We present a complete calculation of weak boson fusion production of
colorless supersymmetric particles at the LHC, using the new matrix element
generator SUSY-MadGraph. The cross sections are small, generally at the
attobarn level, with a few notable exceptions which might provide additional
supersymmetric parameter measurements. We discuss in detail how to consistently
define supersymmetric weak couplings to preserve unitarity of weak gauge boson
scattering amplitudes to fermions, and derive sum rules for weak supersymmetric
couplings.Comment: 24 p., 3 fig., 9 tab., published in PRD; numbers in Table IV
corrected to those with kinematic cuts cite
Schwinger Effect in Non-parallel D1-branes: A Path Integral Approach
We study the Schwinger effect in a system of non-parallel D1-branes for the
bosonic strings using the path integral formalism. We drive the string pair
creation rate by calculating the one loop vacuum amplitude of the setup in
presence of the background electric filed defined along one of the D1-branes.
We find an angle dependent minimum value for the background field and show that
the decaying of vacuum into string pairs takes place for the field above this
value. It is shown that in limit the vacuum
becomes stable and thus no pair creation occurs
In Situ Thermal Decomposition of Exfoliated Two-Dimensional Black Phosphorus
With a semiconducting band gap and high charge carrier mobility,
two-dimensional (2D) black phosphorus (BP), often referred to as phosphorene,
holds significant promise for next generation electronics and optoelectronics.
However, as a 2D material, it possesses a higher surface area to volume ratio
than bulk BP, suggesting that its chemical and thermal stability will be
modified. Herein, an atomic-scale microscopic and spectroscopic study is
performed to characterize the thermal degradation of mechanically exfoliated 2D
BP. From in situ scanning/transmission electron microscopy, decomposition of 2D
BP is observed to occur at ~400 {\deg}C in vacuum, in contrast to the 550
{\deg}C bulk BP sublimation temperature. This decomposition initiates via
eye-shaped cracks along the [001] direction and then continues until only a
thin, amorphous red phosphorous like skeleton remains. In situ electron energy
loss spectroscopy, energy-dispersive X-ray spectroscopy, and energy-loss
near-edge structure changes provide quantitative insight into this chemical
transformation process.Comment: In press: 4 figures in main manuscript, 27 pages with supporting
informatio
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