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{percent}) do exist. The radiative channel turns out to be enhanced when the neutralino tree-level decays are suppressed either {open_quotes}kinematically{close_quotes} or {open_quotes}dynamically.{close_quotes} 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}{approx_equal}1 and/or M{sub 1}{approx_equal}M{sub 2}, and negative values of {mu}. We present typical scenarios where these conditions are satisfied, relaxing the usual relation M{sub 1}=(5/3)tan{sup 2}{theta}{sub W}M{sub 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. {copyright} {ital 1997} {ital The American Physical Society}