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 standard model. We find that significant regions of the supersymmetric parameter space with large radiative branching ratios (up to about 100%) do exist. The radiative channel turns out to be enhanced when the neutralino tree-level decays are suppressed either ''kinematically'' or ''dynamically.'' In general, in the regions allowed by data from CERN LEP and not characterized by asymptotic values of the supersymmetric parameters, 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, relaxing the usual relation m(1)=5/3 tan(2) theta(w)M(2)i.e., gaugino mass unification at the grand unified theory scale. The influence of varying the top-squark masses and mixing angle when the radiative decay is enhanced is also considered. Some phenomenological consequences of the above picture are discussed.