Natural suppression of symmetry violation in gauge theories: Muon and electronleptonnumber nonconservation
Abstract
We analyze the circumstances under which the violations of an approximate symmetry in a unified gauge theory of weak interactions are naturally suppressed; in particular, we investigate approximate muon and electrontype leptonnumber conservation as an example of such a symmetry. Extending earlier work, we propose a unified treatment of this symmetry together with strangeness conservation by the weak neutral current and CP invariance. The rate for the decay μ>eγ is calculated for a general SU(2) × U(1) gauge model. From this and a similar study of the decay μ>eeē we derive a set of conditions which guarantees that the violation of muon and electrontype leptonnumber conservation is naturally strongly suppressed. As part of this, we compute the nondiagonal electromagnetic vertex to oneloop order for an arbitrary SU(2) × U(1) gauge theory. We then focus on the phenomenological predictions of a particular gauge model with three lefthanded doublets of leptons and quarks. These include the existence of charged and neutral heavy leptons and of small violations of μe universality and the relation G^{β}_{F}θ_{C} = G^{μ}_{F}. Other muon and electronnumberviolating effects include nonvanishing rates for the decays K^{+/}>π^{+/}eμ̄ and K_{L}>eμ̄ and for the reactions μ + N>e + N and ν_{μ} + N>e^{} + X.
 Publication:

Physical Review D
 Pub Date:
 September 1977
 DOI:
 10.1103/PhysRevD.16.1444
 Bibcode:
 1977PhRvD..16.1444L