$b\to s\gamma$ Decay in Supersymmetric Theories

Abstract

Recent advances in the calculation of the $b\to s\gamma$ decay branching ratio are presented in the context of supersymmetric theories. Theoretical accuracy increased by inclusion of the next-to-leading order QCD corrections makes it possible to significantly decrease scale dependence of the result. Comparison with the latest CLEO experimental results then allows to limit supersymmetric loop contributions to the process and consequently constrain the parameter space of supersymmetric extensions of the Standard Model. We discuss these constraints both in the minimal supergravity inspired model (SUGRA) and in the simplest gauge-mediated supersymmetry breaking model (GMSB) both of which are interesting from the point of view of the searches for supersymmetry at present and future colliders. Our analysis also includes the interesting region of large $\tan \beta$ relevant for models with Yukawa coupling unification.