Spontaneous Breaking of R parity in the Minimal Supersymmetric Standard Model Revisited

摘要

We reconsider the possibility of spontaneous breaking of $R$ parity in theMinimal Supersymmetric Standard Model. By a renormalization group analysis wefind the parameter space in which a sneutrino gets a vacuum expectation value,leading to the spontaneous breaking of the lepton number and to the appearanceof a phenomenologically unacceptable massless Goldstone boson. We then analyzethe effect of operators giving rise to a tiny amount of explicit violation oflepton number, which could emerge as remnants of physics at some superheavy(Planck or GUT) scale in the low energy effective theory. We show that theconspiracy between the spontaneous and the explicit breaking scales can providea mass to the Goldstone boson larger than the ${\rm Z}^0$ boson mass, henceallowing for a non vanishing sneutrino vacuum expectation value withoutincreasing the invisible width of the ${\rm Z}^0$.