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"Two-loop renormalization of the electric charge in the Standard Model "

Relatore: Dott. Alessandro Vicini- Dip. di Fisica, Un. di Milano

Aula Einstein
03 Febbraio 2004 ore 15.30

We discuss the renormalization of the electric charge at the two-loop level in the Standard Model of the electroweak interactions. We explicitly calculate the expression of the complete on-shell two-loop counterterm using the Background Field Method and discuss the advantages of this computational approach. We consider the related quantity hat e(mu), defined in the MSbar renormalization scheme and present numerical results for different values of the scale mu. We find that the full 2-loop electroweak corrections contribute more than 10 parts in units 10^{-5} to the Delta hatalpha (mz^2) parameter, obtaining hatalpha^{-1}(mz)= 128.12 pm 0.05 for Deltaalpha_{had}(mz^2) =0.027572 pm 0.000359. We briefly comment on the implications for the limits on the Higgs boson mass.