Yukawa unification in SO(10) SUSY GUTs.

摘要

Supersymmetric grand unified models based on the SO(10) gauge group are especially attractive in light of recent data on neutrino masses. The simplest SO(10) SUSY GUT models predict unification of third generation Yukawa couplings (t - b - tau), in addition to the usual gauge coupling unification. An assessment of the viability of such Yukawa unified models is presented. For the superpotential Higgs mass parameter mu > 0, it is found that unification to less than 1% is possible, but only for GUT scale scalar mass parameter m16 ∼8--20 TeV, and small values of gaugino mass m1/2 ≲ 150 GeV. Such models require that a GUT scale mass splitting exists amongst Higgs scalars with m2Hu m2Hd . 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 → sgamma and ( g - 2)mu 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 W1&d15;Z2 &d5; → 3ℓ events, or via gluino pair production. If mu 0, Yukawa coupling unification to less than 5% can occur for m 16 and m1/2 ≳ 1 - 2 TeV. Consistency of negative mu Yukawa unified models with b → sgamma, (g - 2)mu, and relic density Oh2 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. To address the tension between Yukawa unification and the excess of dark matter that the mu > 0 models tend to predict, a couple of possible improvements are surveyed. One solution, lowering the GUT scale mass value of first and second generation scalars, leads to uR and c˜R squark masses in the 90 - 120 GeV regime, which should be accessible to Fermilab Tevatron experiments. Another possibility is relaxing gaugino mass universality which may solve the relic density problem by having neutralino annihilations via the Z or h resonances, or by having a wino-like LSP.