369 research outputs found
Self-duality, Helicity and Higher-loop Euler-Heisenberg Effective Actions
The Euler-Heisenberg effective action in a self-dual background is remarkably
simple at two-loop. This simplicity is due to the inter-relationship between
self-duality, helicity and supersymmetry. Applications include two-loop
helicity amplitudes, beta-functions and nonperturbative effects. The two-loop
Euler-Heisenberg effective Lagrangian for QED in a self-dual background field
is naturally expressed in terms of one-loop quantities. This mirrors similar
behavior recently found in two-loop amplitudes in N=4 SUSY Yang-Mills theory.Comment: 7 pp, latex, axodraw.sty; Based on talks given by G. Dunne at QTS3
(Cincinnati, OH, Sept. 2003) and QFEXT03 (Norman, OK, Sept. 2003
Pair creation in inhomogeneous fields from worldline instantons
We show how to do semiclassical nonperturbative computations within the
worldline approach to quantum field theory using ``worldline instantons''.
These worldline instantons are classical solutions to the Euclidean worldline
loop equations of motion, and are closed spacetime loops parametrized by the
proper-time. Specifically, we compute the imaginary part of the one loop
effective action in scalar and spinor QED using worldline instantons, for a
wide class of inhomogeneous electric field backgrounds.Comment: 10 pages, 2 figures, talk given by C.S. at X Mexican Workshop on
Particles and Fields, Morelia, Mexico, Nov. 6 - 12, 2005 (to appear in the
conference proceedings
Non-Newtonian ice rheology and the retention of craters on Ganymede
Calculations carried out for craters of varying sizes in a medium with constant temperature T = 173 K yield values for the crater relaxation time t sub e (defined as the time required for the crater depth to become 1/e of its original value) that appear to be too small to account for the observed retention of craters on Ganymede and the other icy satellites. Such a calculation is seriously in conflict with the observed crater population of the surfaces of the icy satellites. In an attempt to reconcile this conflict, possible explanations for the much slower relaxation rate of craters on the icy satellites are considered. It is possible that an admixture of silicates in the surface ice regions of the icy satellites may raise the viscosity to some extent. This possible explanation and others are briefly discussed
Evidence for retrograde lithospheric subduction on Venus
Though there is no plate tectonics per se on Venus, recent Magellan radar images and topographic profiles of the planet suggest the occurrence of the plate tectonic processes of lithospheric subduction and back-arc spreading. The perimeters of several large coronae (e.g., Latona, Artemis, and Eithinoha) resemble Earth subduction zones in both their planform and topographic profile. The planform of arcuate structures in Eastern Aphrodite were compared with subduction zones of the East Indies. The venusian structures have radii of curvature that are similar to those of terrestrial subduction zones. Moreover, the topography of the venusian ridge/trench structures is highly asymmetric with a ridge on the concave side and a trough on the convex side; Earth subduction zones generally display the same asymmetry
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