$b \to s\gamma$ with Large tan$\beta$ in MSSM Analysis Constrained by a Realistic SO(10) Model

Study of the MSSM in large tan$\beta$ regime has to include correlations between the constraints presented by the low energy values of the b quark mass and BR($b \to s\gamma$). Both quantities receive SUSY contributions enhanced by tan$\beta$ and have a major impact on the MSSM analysis. Here we summarize the results of such a study constrained by a complete SO(10) model. The dominant effects to the analysis come from third generation Yukawa couplings and a GUT threshold to $\alpha_s$. We show that a small negative GUT correction to $\alpha_s$ accommodates $\alpha_s(M_Z) \leq 0.118$ and $\delta m_b^{SUSY} > 0$. The latter quantity being positive then opens up two options to fit the measured rate for $b \to s\gamma$. The two distinct fits differ by the overall sign of the amplitude for this process. They work equally well in complementary regions of the allowed SUSY parameter space. We show plots of the partial contributions to the coefficient $C_7(M_Z)$ in the ($m_0,M_{1/2}$) plane in each of these best fits. We conclude that an attractive SO(10)-derived regime of the MSSM remains a viable option.