6,893 research outputs found
Direct and Indirect Searches for Low-Mass Magnetic Monopoles
Recently, there has been renewed interest in the search for low-mass magnetic
monopoles. At the University of Oklahoma we are performing an experiment
(Fermilab E882) using material from the old D0 and CDF detectors to set limits
on the existence of Dirac monopoles of masses of the order of 500 GeV. To set
such limits, estimates must be made of the production rate of such monopoles at
the Tevatron collider, and of the binding strength of any such produced
monopoles to matter. Here we sketch the still primitive theory of such
interactions, and indicate why we believe a credible limit may still be
obtained. On the other hand, there have been proposals that the classic
Euler-Heisenberg Lagrangian together with duality could be employed to set
limits on magnetic monopoles having masses less than 1 TeV, based on virtual,
rather than real processes. The D0 collaboration at Fermilab has used such a
proposal to set mass limits based on the nonobservation of pairs of photons
each with high transverse momentum. We critique the underlying theory, by
showing that the cross section violates unitarity at the quoted limits and is
unstable with respect to radiative corrections. We therefore believe that no
significant limit can be obtained from the current experiments, based on
virtual monopole processes.Comment: 20 pages, 1 ps figure, contributed to Kurt Haller's festschrif
Rearranging trees for robust consensus
In this paper, we use the H2 norm associated with a communication graph to
characterize the robustness of consensus to noise. In particular, we restrict
our attention to trees and by systematic attention to the effect of local
changes in topology, we derive a partial ordering for undirected trees
according to the H2 norm. Our approach for undirected trees provides a
constructive method for deriving an ordering for directed trees. Further, our
approach suggests a decentralized manner in which trees can be rearranged in
order to improve their robustness.Comment: Submitted to CDC 201
Theoretical and Experimental Status of Magnetic Monopoles
The Tevatron has inspired new interest in the subject of magnetic monopoles.
First there was the 1998 D0 limit on the virtual production of monopoles, based
on the theory of Ginzberg and collaborators. In 2000 the first results from an
experiment (Fermilab E882) searching for real magnetically charged particles
bound to elements from the CDF and D0 detectors were reported. This also
required new developments in theory. The status of the experimental limits on
monopole masses will be discussed, as well as the limitation of the theory of
magnetic charge at present.Comment: 14 pages, 5 figures, talk given at 5th Workshop on Quantum Field
Theory Under External Condition
Effect of the bat star, Asterina miniata, on recruitment of the giant kelp, Macrocystis pyrifera
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