Dispersion Relations in Loop Calculations

Details Dispersion Relations in Loop Calculations Dispersion Relations in Loop Calculations

1996-07-08

arxiv.org/abs/hep-ph/9607255v1

Acta Phys.Polon.B27:3631-3644,1996

Physics

High Energy Physics

High Energy Physics - Phenomenology

12 pages (Latex), 4 figures (Postscript), lectures delivered at the XXXVI Cracow School of Theoretical Physics, Zakopane, Pola

Scientific paper

These lecture notes give a pedagogical introduction to the use of dispersion relations in loop calculations. We first derive dispersion relations which allow us to recover the real part of a physical amplitude from the knowledge of its absorptive part along the branch cut. In perturbative calculations, the latter may be constructed by means of Cutkosky's rule, which is briefly discussed. For illustration, we apply this procedure at one loop to the photon vacuum-polarization function induced by leptons as well as to the $\gamma f\bar f$ vertex form factor generated by the exchange of a massive vector boson between the two fermion legs. We also show how the hadronic contribution to the photon vacuum polarization may be extracted from the total cross section of hadron production in $e^+e^-$ annihilation measured as a function of energy. Finally, we outline the application of dispersive techniques at the two-loop level, considering as an example the bosonic decay width of a high-mass Higgs boson.

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