Recent Progress in SUSY GUTs

After a brief review of the motivations for grand unification, I discuss the main challenges facing realistic SUSY GUT model building. Achieving doublet-triplet splitting without fine--tuning is chief among them. Symmetry breaking should occur consistently without unwanted Goldston bosons, \mu-term of order TeV for the MSSM Higgs fileds should emerge naturally, and realistic fermion masses with small quark mixing angles and large lepton mixing angles should be generated with some predictivity. Significant progress has been made over the years towards achieving these goals in the context of supersymmetric SO(10) GUT. A complete SO(10) model is presented along this line wherein, somewhat surprisingly, the GUT scale threshold corrections to the gauge couplings are found to be small. This results in a predictive scenario for proton lifetime. An interesting correlation between the d=6 (p\to e^+\pi^0) and d=5 (p\to \nu-bar K^+) decay amplitudes is observed. This class of models predicts that both proton decay modes should be observable with an improvement in the current sensitivity by about a factor of five to ten.