1,766 research outputs found
Revised value of the eighth-order electron g-2
The contribution to the eighth-order anomalous magnetic moment (g-2) of the
electron from a set of diagrams without closed lepton loops is recalculated
using a new FORTRAN code generated by an automatic code generator. Comparing
the contributions of individual diagrams of old and new calculations, we found
an inconsistency in the old treatment of infrared subtraction terms in two
diagrams. Correcting this error leads to the revised value -1.9144 (35)
(alpha/pi)^4 for the eighth-order term. This theoretical change induces the
shift of the inverse of the fine structure constant by -6.41180(73)x10^{-7}.Comment: 4 pages, 1 figure, typo is correcte
Precise mass-dependent QED contributions to leptonic g-2 at order alpha^2 and alpha^3
Improved values for the two- and three-loop mass-dependent QED contributions
to the anomalous magnetic moments of the electron, muon, and tau lepton are
presented. The Standard Model prediction for the electron (g-2) is compared
with its most precise recent measurement, providing a value of the
fine-structure constant in agreement with a recently published determination.
For the tau lepton, differences with previously published results are found and
discussed. An updated value of the fine-structure constant is presented in
"Note added after publication."Comment: 6 pages, 1 figure. v2: New determination of alpha presented (based on
the recent electron g-2 measurement). v3: New formulae added in Sec.IIB. v4:
Updated value of alpha presente
Eighth-Order Vacuum-Polarization Function Formed by Two Light-by-Light-Scattering Diagrams and its Contribution to the Tenth-Order Electron g-2
We have evaluated the contribution to the anomalous magnetic moment of the
electron from six tenth-order Feynman diagrams which contain eighth-order
vacuum-polarization function formed by two light-by-light scattering diagrams
connected by three photons. The integrals are constructed by two different
methods. In the first method the subtractive counter terms are used to deal
with ultraviolet (UV) singularities together with the requirement of
gauge-invariance. In the second method, the Ward-Takahashi identity is applied
to the light-by-light scattering amplitudes to eliminate UV singularities.
Numerical evaluation confirms that the two methods are consistent with each
other within their numerical uncertainties. Combining the two results
statistically and adding small contribution from the muons and/or tau leptons,
we obtain . We also evaluated the
contribution to the muon from the same set of diagrams and found .Comment: 27 page
Percolative behavior of an anisotropic two-dimensional network: Growth of tellurium onto an oriented polymer film
6 pågs.; 9 figs.In situ transport measurements during the growth of a thin layer of thermally evaporated tellurium onto an oriented polymer film are presented. The system, which resembles the characteristics of a two-dimensional anisotropic network, is analyzed in terms of the current percolation theory. Parameters such as the percolation threshold and the critical exponents are calculated for the perpendicular and the parallel orientation. Within the limits of the experiments the values of t℠and t℠are estimated to be 1.15 and 1.46, respectively. ©1997 American Physical SocietyFinancial support by the Volkswagen Foundation and
Comision Interministrial de Ciencia y Tecnologia (Grant No.
MAT94-0825) are gratefully acknowledged.Peer Reviewe
Growth, micro-structuring, spectroscopy, and optical gain in as-deposited waveguides
Deposition and micro-structuring of layers with low background losses (0.11 dB/cm) and lifetimes up to 7 ms have been optimized for active devices. Net gain of 0.7 dB/cm at 1533 nm has been measured.\ud
\u
What happens during a blackout: Consequences of a prolonged and wide-ranging power outage
Power outages in Europe and North America in recent years have given a lasting impression of the vulnerability of modern and high-tech societies. Although the power supply was interrupted for a week at most and only locally, massive functional and supply disruptions, threats to public order and damage amounting to billions of euros have already become apparent. This book shows what consequences a prolonged and widespread power blackout could have on society and its critical infrastructures and how Germany is prepared for such a large-scale disaster. By means of comprehensive consequence analyses, the authors drastically demonstrate that after only a few days, the supply of the population with (vital) goods and services can no longer be guaranteed in the affected area. It is also made clear that considerable efforts are required to increase the sustainability of critical infrastructures and to further optimise the capacities of the national disaster management system.
The book is based on TAB Report Nr. 141 "GefĂ€hrdung und Verletzbarkeit moderner Gesellschaften - am Beispiel eines groĂrĂ€umigen und langandauernden Ausfalls der Stromversorgung"
- âŠ