10,542 research outputs found
Unnatural Acts: Unphysical Consequences of Imposing Boundary Conditions on Quantum Fields
I examine the effect of trying to impose a Dirichlet boundary condition on a
scalar field by coupling it to a static background. The zero point -- or
Casimir -- energy of the field diverges in the limit that the background forces
the field to vanish. This divergence cannot be absorbed into a renormalization
of the parameters of the theory. As a result, the Casimir energy of a surface
on which a Dirichlet boundary condition is imposed, and other quantities like
the surface tension, which are obtained by deforming the surface, depend on the
physical cutoffs that characterize the coupling between the field and the
matter on the surface. In contrast, the energy density away from the surface
and forces between rigid surfaces are finite and independent of these
complicationsComment: 10 pages, 3 figures, uses aipproc.cls which is included in upload.
allnew.eps replaces figures all.eps and section.ep
Color, Spin, and Flavor-Dependent Forces in Quantum Chromodynamics
A simple generalization of the Breit Interaction explains many qualitative
features of the spectrum of hadrons.Comment: 20 pp., 8 EPS figures, LaTeX2e using BoxedEPS, ws-p8-50x6-00.cls
macros; contribution to forthcoming published lectures of the Gregory Breit
Centennial Symposium, October 1999; email to [email protected]
Comment on the relation between the nonadiabatic coupling and the complex intersection of potential energy curves
Simple relations are discussed that provide a correspondence between the complex intersection of two potential surfaces and the nonadiabatic coupling matrix element between those surfaces. These are key quantities in semiclassical and quantum mechanical theories of collision induced electronic transitions. Within the two state approximation, the complex intersection is shown to be directly related to the location and magnitude of the peak in the nonadiabatic coupling. Two cases are considered: the avoided crossing between two potential surfaces; and the spin orbit interaction due to a P-2 halogen atom. Comparisons are made between the results of the two-state model and the results of ab initio quantum chemical calculations
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