1,856 research outputs found
A No-Go Theorem for M5-brane Theory
The BLG model for multiple M2-branes motivates an M5-brane theory with a
novel gauge symmetry defined by the Nambu-Poisson structure. This Nambu-Poisson
gauge symmetry for an M5-brane in large C-field background can be matched, on
double dimension reduction, with the Poisson limit of the noncommutative gauge
symmetry for a D4-brane in B-field background. Naively, one expects that there
should exist a certain deformation of the Nambu-Poisson structure to match with
the full noncommutative gauge symmetry including higher order terms. However,
We prove the no-go theorem that there is no way to deform the Nambu-Poisson
gauge symmetry, even without assuming the existence of a deformation of
Nambu-Poisson bracket, to match with the noncommutative gauge symmetry in 4+1
dimensions to all order, regardless of how the double dimension reduction is
implemented.Comment: v4: minor modifications
Comments on the topological open membrane
Just as non-commutative gauge theories arise from quantising open strings in
a large magnetic field, non-Abelian two-form gauge theories may conceivably be
constructed by quantising open membranes in a large three-form magnetic
background. We make some observations that arise in following this strategy,
with an emphasis on the relation to the quantisation of volume-preserving
diffeomorphisms (vpd). In particular, we construct consistent non-Abelian
interactions of a two-form in 3+1 dimensions, based on gauge invariance under
vpd.Comment: 6 pages, latex2e, uses revtex
Monolithic Integration of Collimating Fresnel Lens for Beam Quality Enhancement in Tapered High Power Laser Diode
We demonstrate, for the first time, a monolithic integrated lens for wide aperture gain-guided tapered laser beam quality enhancement by compensating the quadratic phase curvature. The 3mm long tapered laser with an output aperture of 170µm adopted in this design consists of a gain-guided tapered section and an index-guided ridge section and operated at 980nm. The lens design is implemented by focus ion beam etching (FIBE) technique, whereby the laser diode is mounted p-side up in order to facilitate the etching process. The lens is located 600µm away from the junction of the tapered and ridge sections, and is 40µm wide and 300µm long with a focal length of 800µm. The laser diode is characterised by light-current characteristics together with near- and far- field measurements before and after etching. The device is biased by current pulses of 1µs width and 0.1% duty cycle. Light-current measurement shows a drop of 10.5% in threshold current from 380mA to 340mA after the inclusion of lens. This is an evidence that the lens effectively equalised the curved phase in order to reduce the laser cavity loss by improving the coupling efficiency of backward travelling wave at the output facet. Throughout the whole current range tested, the width of near-field at waist is broadened by an average of 36% after the inclusion of lens. By successfully compensating the quadratic phase curvature of the mode, the beam divergence in the far-field is significantly narrowed by an average of 28.5%. M2 factor is improved by an average of 12
Formation of the in Two-Photon Collisions at LEP
The two-photon width of the meson has been
measured with the L3 detector at LEP. The is studied in the decay
modes , KK, KK,
KK, , , and
using an integrated luminosity of 140 pb at GeV and
of 52 pb at GeV. The result is
(BR) keV. The dependence of the cross section is studied for
GeV. It is found to be better described by a Vector Meson
Dominance model form factor with a J-pole than with a -pole. In addition,
a signal of events is observed at the mass. Upper limits
for the two-photon widths of the , , and are also
given
Search for Low Scale Gravity Effects in e+e- Collisions at LEP
Recent theories propose that quantum gravity effects may be observable at LEP
energies via gravitons that couple to Standard Model particles and propagate
into extra spatial dimensions. The associated production of a graviton and a
photon is searched for as well as the effects of virtual graviton exchange in
the processes: e+e- -> gamma gamma, ZZ, WW, mu mu, tau tau, qq and ee No
evidence for this new interaction is found in the data sample collected by the
L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1
TeV on the scale of this new scenario of quantum gravity are set
Search for Scalar Leptons in e+e- collisions at \sqrt{s}=189 GeV
We report the result of a search for scalar leptons in e+e- collisions at 189
GeV centre-of-mass energy at LEP. No evidence for such particles is found in a
data sample of 176 pb^{-1}. Improved upper limits are set on the production
cross sections for these new particles. New exclusion contours in the parameter
space of the Minimal Supersymmetric Standard Model are derived, as well as new
lower limits on the masses of these supersymmetric particles. Under the
assumptions of common gaugino and scalar masses at the GUT scale, we set an
absolute lower limit on the mass of the lightest scalar electron of 65.5 Ge
Study of Z Boson Pair Production in e+e- Collisions at LEP at \sqrt{s}=189 GeV
The pair production of Z bosons is studied using the data collected by the L3
detector at LEP in 1998 in e+e- collisions at a centre-of-mass energy of 189
GeV. All the visible final states are considered and the cross section of this
process is measured to be 0.74 +0.15 -0.14 (stat.) +/- 0.04 (syst.) pb. Final
states containing b quarks are enhanced by a dedicated selection and their
production cross section is found to be 0.18 +0.09 -0.07 (stat.) +/- 0.02
(syst.) pb. Both results are in agreement with the Standard Model predictions.
Limits on anomalous couplings between neutral gauge bosons are derived from
these measurements
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