Effects of supersymmetric grand unification scale physics on $Gamma left( bto sgammaright)$.pdf

a r X i v : h e p - p h / 9 5 0 2 2 3 9 v 2 3 0 O c t 1 9 9 5 July 1995 OSU-298 UCRHEP-T139 Effects of supersymmetric grand unification scale physics on Γ (b → sγ) B. Dutta? and E. Keith ? ? Department of Physics Oklahoma State University Stillwater, OK 74078 ? Department of Physics University of California Riverside, CA 92521 ABSTRACT Although calculations of the b → sγ rate in supersymmetric grand unified models have always either ignored the gluino mediated contribution or found it to be negligible, we show that taking universal supersymmetry breaking masses at the Planck scale, rather than at the gauge unification scale as is customary, leads to the gluino contribution being more significant and in fact sometimes even larger than the chargino mediated contributions when μ 0 and tan β is of order 1. The impact is greatest felt when the gluinos are relatively light. Taking the universal boundary condition at the Planck scale also has an effect on the chargino contribution by increasing the effect of the wino and higgsino- wino mediated decays. The neutralino mediated contribution is found to be enhanced, but nevertheless it remains relatively insignificant. The flavor changing decay b → sγ is often an important test of new physics because it is rapid enough to be experimentally observable although it appears first at the one loop level in the standard model (SM), thus allowing new physics to add sizeable corrections to it. For example, the decay is useful to limit parameter space in the minimal supersymmetric standard model (MSSM) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]. This is an especially useful tool if certain constraints have already been placed on the MSSM. Since the decay vanishes in the limit of unbroken supersymmetry, the relevant constraints pertain to the terms in the Lagrangian that softly break supersymmetry (SUSY). The general soft SUSY breaking scalar interactions for squarks and sleptons in the MSSM are of the following form: Vsoft = Q(AUλU)U cH