B→Xsγ in supersymmetry: large contributions beyond the leading order

We discuss possible large contributions to B -> X_s gamma, which can occur atthe next-to-leading order in supersymmetric models. They can originate fromterms enhanced by tan(beta) factors, when the ratio between the two Higgsvacuum expectation values is large, or by logarithm of M_{susy}/M_W, when thesupersymmetric particles are considerably heavier than the W boson. We givecompact formulae which include all potentially large higher-ordercontributions. We find that tan(beta) terms at the next-to-leading order do notonly appear from the Hall-Rattazzi-Sarid effect (the modified relation betweenthe bottom mass and Yukawa coupling), but also from an analogous effect in thetop-quark Yukawa coupling. Finally, we show how next-to-leading ordercorrections, in the large tan(beta) region, can significantly reduce the limiton the charged-Higgs mass, even if supersymmetric particles are very heavy.Comment: 18 pages, 5 figs, extended discussion of light stop case, notational improvement