878 research outputs found
Level Splitting in Association with the Multiphoton Bloch-Siegert Shift
We present a unitary equivalent spin-boson Hamiltonian in which terms can be
identified which contribute to the Bloch-Siegert shift, and to the level
splittings at the anticrossings associated with the Bloch-Siegert resonances.
First-order degenerate perturbation theory is used to develop approximate
results in the case of moderate coupling for the level splitting.Comment: 8 pages, 2 figure
Dissecting the hadronic contributions to by Schwinger's sum rule
The theoretical uncertainty of is currently dominated by
hadronic contributions. In order to express those in terms of directly
measurable quantities, we consider a sum rule relating to an integral of
a photo-absorption cross section. The sum rule, attributed to Schwinger, can be
viewed as a combination of two older sum rules: Gerasimov-Drell-Hearn and
Burkhardt-Cottingham. The Schwinger sum rule has an important feature,
distinguishing it from the other two: the relation between the anomalous
magnetic moment and the integral of a photo-absorption cross section is linear,
rather than quadratic. The linear property makes it suitable for a
straightforward assessment of the hadronic contributions to . From
the sum rule we rederive the Schwinger correction, as well as the
formula for the hadronic vacuum-polarization contribution. As an example of the
light-by-light contribution we consider the single-meson exchange.Comment: 6 pages, 10 figures, published version extended by a few clarifying
remarks and an Appendi
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