The electric charge at the two-loop level in the Standard Model and the precision measurements of Delta alpha_{had}

Abstract

The complete calculation of the 2-loop electroweak corrections to the renormalization of the electric charge in the Standard Model allows to discuss in detail the value of the MSbar effective coupling $\hat{e}(m_Z)$. We discuss the phenomenological impact of these results in view of the increasing accuracy in the measurements of the cross-section of the reaction e+e- -->hadrons at low energies.

Comments: Talk given at the workshop SIGHAD03, Pisa, 8-10 October 2003, two references added