Applications of the Goldstone equivalence theorem to scattering and decay processes
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- Institutt for fysikk 
We study applications of the Goldstone boson equivalence theorem to decay and scattering processes, exemplifying the broken gauge theory structure of electroweak interactions.Apart from interest on theoretical grounds, we are motivated by the problem ofthe dark matter identity, and the importance of electroweak bremsstrahlungcontributions to dark matter annihilation. Higgs decay into charged gauge bosons isapproached using four separate methods, including the utilisation of theequivalence theorem, and we show that the results of all approaches agree.Furthermore, the equivalence theorem is applied to electroweak bremsstrahlungcorrections in the specific process of quark production from electron-positronannihilation. We find that the emission of the Goldstone boson intrinsicallyhas the appropriate high-energy behaviour, in contrast to the longitudinalcomponent of the massive gauge boson. Thus, the equivalence theorem necessitatea cancellation of the longitudinal contributions from all sub-processes at agiven order in perturbation theory.