New limits on the SUSY Higgs boson mass

We present new upper limits on the light Higgs boson mass m(h) in supersymm etric models. We consider two gravity-mediated models (with and without uni versal scaler masses) and two gauge-mediated models (with a 5+(5) over bar or 10 + (1) over bar 0 messenger sector). We impose standard phenomenologic al constraints, as well as SU(5) Yukawa coupling unification. Requiring tha t the bottom and tau Yukawa couplings meet at the unification scale to with in 15%, we find the upper limit m(h) < 114 GeV in the universal supergravit y model. This reverts to the usual upper bound of 130 GeV with a particular nonuniversality in the scalar spectrum. In the 5 + (5) over bar gauge-medi ated model we find m(h) < 97 GeV for small tan beta and m(h) similar or equ al to 116 GeV for large tan beta, and in the 10 + (1) over bar 0 model we f ind m(h) < 94 GeV. We discuss the implications for upcoming searches at LEP -II and the Tevatron. (C) 1999 Elsevier Science B.V. All rights reserved.