(MU(-),E(-)) CONVERSION - A SYMBIOSIS OF PARTICLE-PHYSICS AND NUCLEAR-PHYSICS

(mu(-),e(-)) conversion is the experimentally most interesting lepton flavor violating process. From a theoretical point of view it is an in teresting interplay of particle and nuclear physics. The effective tra nsition operator, depending on the gauge model, is in general describe d in terms of a combination of four terms (isoscalar and isovector, Fe rmi-like as well as axial vector-like). The experimentally most intere sting ground state to ground state transition is adequately described in terms of the usual proton and neutron form factors. These were comp uted in both the shell model and RPA. Since it is of interest to know the portion of the strength exhausted by the coherent (ground state to ground state) transition, the total transition rate to all final stat es must also be computed. This was done (i) in RPA by explicitly summi ng over all final states (ii) in the context of the closure approximat ion (using shell model and RPA for constructing the initial state), an d (iii) in the context of nuclear matter mapped into nuclei via a loca l density approximation. We found that, apart from small local oscilla tions, the conversion rate keeps increasing from light to heavy nuclea r elements. We also find that the coherent mode is dominant (it exhaus ts more than 90% of the sum rule). Various gauge models are discussed. In general the predicted branching ratio is much smaller compared to the present experimental limit.