About the relevance of the Imaginary components of the effective couplings in the Asymmetry measurements

The effect coming from imaginary parts of effective couplings in the $e^+ e^-$ asymmetries is investigated. It is shown that for the present level of experimental accuracy, in some asymmetries the imaginary parts of the effective couplings cannot be neglected and moreover that the use of different prescriptions on how to handle them in quoting just real effective couplings from the data may produce sizable differences. A definition of the real effective couplings specifying how to handle the imaginary parts is advocated.