HIP-1998-75/TH TECHNION-PH-25 December 7, 1998 b → ss ¯ d Decay in Two Higgs Doublet Models Katri Huitu a , Cai-Dian L¨ u b,d1 , Paul Singer c and Da-Xin Zhang a,d a Helsinki Institute of Physics, P.O.Box 9, FIN-00014 University of Helsinki, Finland b II. Institut f¨ ur Theoretische Physik, Universit¨at Hamburg, 22761 Hamburg, Germany c Department of Physics, Technion- Israel Institute of Technology, Haifa 32000, Israel d The Abdus Salam International Centre for Theoretical Physics P.O. Box 586, 34100 Trieste, Italy Abstract In the Standard Model, the box-diagram mediated decay b → ss ¯ d is predicted to occur with an extremely small branching ratio of below 10 -11 , thus providing a safe testing ground for exposing new physics. We study this process in several Two Higgs Doublet Models and explore their parameter space, indicating where this process becomes observable. 1 Alexander von Humboldt research fellow. 1