Heavy particles and the ro-parameter in the standard model

Abstract

A new formalism is presented for the calculation of the contribution to from heavy particles transforming according to arbitrary representations of . A conjecture for the necessary and sufficient conditions that for all values of masses and mixing angles within a particular multiplet is formulated. A number of examples are given (all consistent with the conjecture) and the significance of improved knowledge of vis a vis the possible existence of undiscovered heavy particles discussed.