41,259 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
A strongly inhomogeneous superfluid in an iron-based superconductor
Among the mysteries surrounding unconventional, strongly correlated
superconductors is the possibility of spatial variations in their superfluid
density. We use atomic-resolution Josephson scanning tunneling microscopy to
reveal a strongly inhomogeneous superfluid in the iron-based superconductor
FeTe0.55Se0.45. By simultaneously measuring the topographic and electronic
properties, we find that this inhomogeneity in the superfluid density is not
caused by structural disorder or strong inter-pocket scattering, and does not
correlate with variations in Cooper pair-breaking gap. Instead, we see a clear
spatial correlation between superfluid density and quasiparticle strength,
putting the iron-based superconductors on equal footing with the cuprates and
demonstrating that locally, the quasiparticles are sharpest when the
superconductivity is strongest. When repeated at different temperatures, our
technique could further help elucidate what local and global mechanisms limit
the critical temperature in unconventional superconductors
Stability of the Magnetic Monopole Condensate in three- and four-colour QCD
It is argued that the ground state of three- and four-colour QCD contains a
monopole condensate, necessary for the dual Meissner effect to be the mechanism
of confinement, and support its stability on the grounds that it gives the
off-diagonal gluons an effective mass sufficient to remove the unstable ground
state mode.Comment: jhep.cls, typos corrected, references added, some content delete
More on Chiral-Nonchiral Dual Pairs
Expanding upon earlier work of Pouliot and Strassler, we construct chiral
magnetic duals to nonchiral supersymmetric electric theories based upon SO(7),
SO(8) and SO(9) gauge groups with various numbers of vector and spinor matter
superfields. Anomalies are matched and gauge invariant operators are mapped
within each dual pair. Renormalization group flows along flat directions are
also examined. We find that confining phase quantum constraints in the electric
theories are recovered from semiclassical equations of motion in their magnetic
counterparts when the dual gauge groups are completely Higgsed.Comment: 25 pages, harvmac and tables macros, 1 figur
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
Geometrical properties of the trans-spherical solutions in higher dimensions
We investigate the geometrical properties of static vacuum -brane
solutions of Einstein gravity in dimensions, which have spherical
symmetry of orthogonal to the -directions and are invariant under
the translation along them. % The solutions are characterized by mass density
and tension densities. % The causal structure of the higher dimensional
solutions is essentially the same as that of the five dimensional ones. Namely,
a naked singularity appears for most solutions except for the Schwarzschild
black -brane and the Kaluza-Klein bubble. % We show that some important
geometric properties such as the area of and the total spatial volume
are characterized only by the three parameters such as the mass density, the
sum of tension densities and the sum of tension density squares rather than
individual tension densities. These geometric properties are analyzed in detail
in this parameter space and are compared with those of 5-dimensional case.Comment: 14 pages, 2 figures, Title change
Amplifier for scanning tunneling microscopy at MHz frequencies
Conventional scanning tunneling microscopy (STM) is limited to a bandwidth of
circa 1kHz around DC. Here, we develop, build and test a novel amplifier
circuit capable of measuring the tunneling current in the MHz regime while
simultaneously performing conventional STM measurements. This is achieved with
an amplifier circuit including a LC tank with a quality factor exceeding 600
and a home-built, low-noise high electron mobility transistor (HEMT). The
amplifier circuit functions while simultaneously scanning with atomic
resolution in the tunneling regime, i.e. at junction resistances in the range
of giga-ohms, and down towards point contact spectroscopy. To enable high
signal-to-noise and meet all technical requirements for the inclusion in a
commercial low temperature, ultra-high vacuum STM, we use superconducting
cross-wound inductors and choose materials and circuit elements with low heat
load. We demonstrate the high performance of the amplifier by spatially mapping
the Poissonian noise of tunneling electrons on an atomically clean Au(111)
surface. We also show differential conductance spectroscopy measurements at
3MHz, demonstrating superior performance over conventional spectroscopy
techniques. Further, our technology could be used to perform impedance matched
spin resonance and distinguish Majorana modes from more conventional edge
states
Tip-Induced Modifications in Scanning Tunneling Microscopy and Atomic Force Microscopy
Tip-induced modifications of microscopic processes in scanning tunneling microscopy (STM) and atomic force microscopy (AFM) of the Si(l00) surface are investigated with ab initio total energy pseudopotential calculations. The results of the calculations lead to a new understanding of the microscopic STM measurement process and the micro-mechanical changes (hysteresis and plastic deformation) in the AFM process. In particular, in the latter case, the results predict that the tip can be used to flip dimers on the surface, from one buckled configuration to the other, reversibly, and without inducing damage to either the intrinsic surface or the tip
Abelian Dominance in Wilson Loops
It has been conjectured that the Abelian projection of QCD is responsible for
the confinement of color. Using a gauge independent definition of the Abelian
projection which does {\it not} employ any gauge fixing, we provide a strong
evidence for the Abelian dominance in Wilson loop integral. In specific we
prove that the gauge potential which contributes to the Wilson loop integral is
precisely the one restricted by the Abelian projection.Comment: 4 pages, no figure, revtex. Phys. Rev. D in pres
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