Showing papers on "Schwinger variational principle published in 1999"
TL;DR: Zhou et al. as discussed by the authors used the Schwinger variational principle for rearrangement collisions to study positronium formation in positron-hydrogen collisions at low energies in the range 6.8-10.2 eV.
Abstract: The Schwinger variational principle for rearrangement collisions is used to study positronium formation in positron-hydrogen collisions at low energies in the range 6.8-10.2 eV. A total number of eight terms of correlated functions in the direct and rearrangement channels in a discrete basis set expansion is found to be sufficient to predict accurate cross sections for S, P, D, and higher partial waves up to L = 14 in agreement with the Kohn-Hulthen variational results available in the literature. Our findings indicate that destructive interference between partial-wave contributions to the scattering amplitude is responsible for the appearance of critical angles in positronium formation. The surface plot of the differential cross section for positronium formation displays rich structure. The predicted total cross sections are in conformity with the observed data of the Wayne State group (Zhou et al 1999 Phys. Rev. A 55 361).
7 citations
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TL;DR: The Peierls bracket as discussed by the authors is defined in terms of Green's functions for the Jacobi field operator and it is applicable to bosonic and fermionic observables equally.
Abstract: The Peierls bracket, defined in terms of Green’s functions for the Jacobi field operator, is presented as a global replacement for the conventional Poisson bracket of field theory. It is applicable to bosonic and fermionic observables equally. It is as well defined for systems with constraints as those without. If the constraints are associated with local invariances it is defined for observables (invariants) only, and its use avoids the necessity of introducing (1) brackets for non-observables and (2) bigger-than-physical Hilbert or Fock spaces. It also carries one easily, indeed irresistably, forward to the quantization rules embodied in the Schwinger variational principle and the Feynman sum over histories.
3 citations
TL;DR: In contrast to the first Born approximation predicted quadratic enhancement, saturation has been observed in the excitation cross-sections of 120 MeV S14+ ions in interaction with gas targets as mentioned in this paper.
Abstract: In contrast to the first Born approximation predicted quadratic enhancement, saturation has been observed in the excitation cross-sections of 120 MeV S14+ ions in interaction with gas targets. The measured cross-sections agree with the theoretical calculations in the framework of the Schwinger variational principle. The symmetric eikonal CDW approximation, however, underestimates the cross-sections with the heavier target atoms.
1 citations