Yukawa coupling unification in supersymmetric models

Abstract

We present an updated assessment of the viability of t - b - τ Yukawa coupling unification in supersymmetric models. For the superpotential Higgs mass parameter μ > 0, we find unification to less than 1% is possible, but only for GUT scale scalar mass parameter m16 ∼ 8 - 20TeV, and small values of gaugino mass m1/2 ≲ 400 GeV. Such models require that a GUT scale mass splitting exists amongst Higgs scalars with m2 Hu2 < mHd2. Viable solutions lead to a radiatively generated inverted scalar mass hierarchy, with third generation and Higgs scalars being lighter than other sfermions. These models have very heavy sfermions, so that unwanted flavor changing and CP violating SUSY processes are suppressed, but may suffer from some fine-tuning requirements. While the generated spectra satisfy b → Sγ and (g - 2)μ constraints, there exists tension with the dark matter relic density unless m16 ≲ 3 TeV. These models offer prospects for a SUSY discovery at the Fermilab Tevatron collider via the search for W̃1Z̃2 → 3ℓ events, or via gluino pair production. If μ < 0, Yukawa coupling unification to less than 5% can occur for m16 and m1/2 ≳ 1 - 2 TeV. Consistency of negative μ Yukawa unified models with b → sγ, (g - 2) μ, and relic density Ωh2 all imply very large values of m1/2 typically greater than about 2.5 TeV, in which case direct detection of sparticles may be a challenge even at the LHC. © SISSA/ISAS 2003.