SUPERSYMMETRIC SCENARIOS WITH DOMINANT RADIATIVE NEUTRALINO DECAY

The radiative decay of the next-to-lightest neutralino into a lightest neutralino and a photon is analyzed in the minimal supersymmetric sta ndard model. We find that significant regions of the supersymmetric pa rameter space with large radiative branching ratios (up to about 100%) do exist. The radiative channel turns out to be enhanced when the neu tralino tree-level decays are suppressed either ''kinematically'' or ' 'dynamically.'' In general, in the regions allowed by data from CERN L EP and not characterized by asymptotic values of the supersymmetric pa rameters, the radiative enhancement requires tan beta similar or equal to 1 and/or M(1) similar or equal to M(2), and negative values of mu. We present typical scenarios where these conditions are satisfied, re laxing the usual relation m(1)=5/3 tan(2) theta(w)M(2)i.e., gaugino ma ss unification at the grand unified theory scale. The influence of var ying the top-squark masses and mixing angle when the radiative decay i s enhanced is also considered. Some phenomenological consequences of t he above picture are discussed.