In simple SO(10) SUSY GUTs the top, bottom and tau Yukawa couplings unify at the GUT scale. A naive renormalization group analysis, neglecting weak scale threshold corrections, leads to moderate agreement with the low energy data. However it is known that intrinsically large threshold corrections proportional to $\tan\beta \sim m_t(M_Z)/m_b(M_Z) \sim 50$ can nullify these $t, b$, $\tau$ mass predictions. In this paper we turn the argument around. Instead of predicting fermion masses, we use the constraint of Yukawa unification and the observed values $M_t, m_b(m_b), M_\tau$ to constrain SUSY parameter space. We find a narrow region survives for $\mu > 0$ with $\mu, M_{ 1/2} << m_{ 16}$, $A_0 \approx - 1.9 m_{ 16}$ and $m_{ 16} > 1200$ \gev. Demanding Yukawa unification thus makes definite predictions for Higgs and sparticle masses. In particular we find a light higgs with mass $m_h^0 = 114 \pm 5 \pm 3$ GeV and a light stop with $(m_{ \tilde t_1})_{ MIN} \sim 450$ GeV and $m_{ \tilde t_1} << m_{ \tilde b_1}$. In addition, we find a light chargino and a neutralino LSP. It is also significant that in this region of parameter space the SUSY contribution to the muon anomalous magnetic moment $a_\mu^{ SUSY} < 16 \times 10^{ -10}$.
Categories: hep-ph