Theory of stability of tensor operators under perturbations and its application to particle physics

Abstract

We investigate the perturbations of tensor operators due to symmetry breaking and consequent representation mixing. A group-theoretical stability principle, valid for an arbitrary (simple, compact) group is formulated, which in many cases assures the vanishing of the first-order perturbation when it is constrained to leave a certain component unaltered. The physically interesting case of unitary symmetry is discussed in detail. All previously known results are recovered and several new results are deduced. As an application we discuss the conditions under which the universality of the Cabibbo angles for leptonic decays is valid.