The most general SU(2)ΓU(1)Yβ-symmetric quartic potential with two
Higgs doublets, subject to an only softly broken discrete symmetry
(Ο1β,Ο2β)β(βΟ1β,Ο2β), is considered. At tree-level, analytic
bounds on the parameters are derived that ensure a stable vacuum, breaking
SU(2)ΓU(1)Yβ down to U(1)emβ.Comment: from last year, but due to recent interest now on the e-print
archive, 8 pages, no figures, plain late