60,820 research outputs found
Single W Production at LEP2
Single W and single gamma productions which are sensitive to the trilinear
gauge coupling WWgamma have been studied at LEP. It isshown that single W
production has particular sensitivity to the "anomalous" magnetic moment Kgamma
of the W boson, complementary to WW production at LEP and Wgamma production at
hadron colliders. The invisible decay of W boson has been searched and the
limit on the invisible decay width of 27 MeV at 95% C.L. has been obtained.Comment: 5 pages, 10 figures, talk given at the XXIX International Conference
on High Energy Physics, July 23-29, 1998, Vancouver, Canad
Transport through a single Anderson impurity coupled to one normal and two superconducting leads
We study the interplay between the Kondo and Andreev-Josephson effects in a
quantum dot coupled to one normal and two superconducting (SC) leads. In the
large gap limit, the low-energy states of this system can be described exactly
by a local Fermi liquid for the interacting Bogoliubov particles. The phase
shift and the renormalized parameters for the Bogoliubov particles vary
depending on the Josephson phase between the two SC leads. We explore the
precise features of a crossover that occurs between the Kondo singlet and local
Cooper-pairing states as the Josephson phase varies, using the numerical
renormalization group approach.Comment: 4 pages, 4 figures, contribution to SCES 201
Homogeneous SPC/E water nucleation in large molecular dynamics simulations
We perform direct large molecular dynamics simulations of homogeneous SPC/E
water nucleation, using up to molecules. Our large system
sizes allow us to measure extremely low and accurate nucleation rates, down to
, helping close the gap between
experimentally measured rates .
We are also able to precisely measure size distributions, sticking
efficiencies, cluster temperatures, and cluster internal densities. We
introduce a new functional form to implement the Yasuoka-Matsumoto nucleation
rate measurement technique (threshold method). Comparison to nucleation models
shows that classical nucleation theory over-estimates nucleation rates by a few
orders of magnitude. The semi-phenomenological nucleation model does better,
under-predicting rates by at worst, a factor of 24. Unlike what has been
observed in Lennard-Jones simulations, post-critical clusters have temperatures
consistent with the run average temperature. Also, we observe that
post-critical clusters have densities very slightly higher, , than
bulk liquid. We re-calibrate a Hale-type vs. scaling relation using
both experimental and simulation data, finding remarkable consistency in over
orders of magnitude in the nucleation rate range, and K in the
temperature range.Comment: Accepted for publication in the Journal of Chemical Physic
The spectrum of gravitational waves in Randall-Sundrum braneworld cosmology
We study the generation and evolution of gravitational waves (tensor
perturbations) in the context of Randall-Sundrum braneworld cosmology. We
assume that the initial and final stages of the background cosmological model
are given by de Sitter and Minkowski phases, respectively, and they are
connected smoothly by a radiation-dominated phase. This setup allows us to
discuss the quantum-mechanical generation of the perturbations and to see the
final amplitude of the well-defined zero mode. Using the Wronskian formulation,
we numerically compute the power spectrum of gravitational waves, and find that
the effect of initial vacuum fluctuations in the Kaluza-Klein modes is
subdominant, contributing not more than 10% of the total power spectrum. Thus
it is confirmed that the damping due to the Kaluza-Klein mode generation and
the enhancement due to the modification of the background Friedmann equation
are the two dominant effects, but they cancel each other, leading to the same
spectral tilt as the standard four-dimensional result. Kaluza-Klein gravitons
that escape from the brane contribute to the energy density of the dark
radiation at late times. We show that a tiny amount of the dark radiation is
generated due to this process.Comment: 10 pages, 5 figures; v2: published versio
Escape of black holes from the brane
TeV-scale gravity theories allow the possibility of producing small black
holes at energies that soon will be explored at the LHC or at the Auger
observatory. One of the expected signatures is the detection of Hawking
radiation, that might eventually terminate if the black hole, once perturbed,
leaves the brane. Here, we study how the `black hole plus brane' system evolves
once the black hole is given an initial velocity, that mimics, for instance,
the recoil due to the emission of a graviton. The results of our dynamical
analysis show that the brane bends around the black hole, suggesting that the
black hole eventually escapes into the extra dimensions once two portions of
the brane come in contact and reconnect. This gives a dynamical mechanism for
the creation of baby branes.Comment: 4 pages, 6 figure
Magnetic-Field Induced Gap in One-Dimensional Antiferromagnet KCuGaF
Magnetic susceptibility and specific heat measurements in magnetic fields
were performed on an one-dimensional antiferromagnet KCuGaF.
Exchange interaction was evaluated as K. However, no
magnetic ordering was observed down to 0.46 K. It was found that an applied
magnetic field induces a staggered magnetic susceptibility obeying the Curie
law and an excitation gap, both of which should be attributed to the
antisymmetric interaction of the Dzyaloshinsky-Moriya type and/or the staggered
-tensor. With increasing magnetic field , the gap increases almost in
proportion to .Comment: Submitted to Proceedings of Research in High Magnetic Fiel
Spatial gene drives and pushed genetic waves
Gene drives have the potential to rapidly replace a harmful wild-type allele
with a gene drive allele engineered to have desired functionalities. However,
an accidental or premature release of a gene drive construct to the natural
environment could damage an ecosystem irreversibly. Thus, it is important to
understand the spatiotemporal consequences of the super-Mendelian population
genetics prior to potential applications. Here, we employ a reaction-diffusion
model for sexually reproducing diploid organisms to study how a locally
introduced gene drive allele spreads to replace the wild-type allele, even
though it possesses a selective disadvantage . Using methods developed by
N. Barton and collaborators, we show that socially responsible gene drives
require , a rather narrow range. In this "pushed wave" regime, the
spatial spreading of gene drives will be initiated only when the initial
frequency distribution is above a threshold profile called "critical
propagule", which acts as a safeguard against accidental release. We also study
how the spatial spread of the pushed wave can be stopped by making gene drives
uniquely vulnerable ("sensitizing drive") in a way that is harmless for a
wild-type allele. Finally, we show that appropriately sensitized drives in two
dimensions can be stopped even by imperfect barriers perforated by a series of
gaps
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