Confronting electroweak fine-tuning with No-Scale Supergravity

Abstract Applying No-Scale Supergravity boundary conditions at a heavy unification scale to the Flipped SU ( 5 ) grand unified theory with extra TeV-scale vector-like multiplets, i.e. No-Scale F - SU ( 5 ) , we express the Z -boson mass M Z as an explicit function of the boundary gaugino mass M 1 / 2 , M Z 2 = M Z 2 ( M 1 / 2 2 ) , with implicit dependence upon a dimensionless ratio c of the supersymmetric Higgs mixing parameter μ and M 1 / 2 . Setting the top Yukawa coupling consistent with m t = 174.3 GeV at M Z = 91.2 GeV , the value of c naturally tends toward c ≃ 1 , which indirectly suggests underlying action of the Giudice–Masiero mechanism. Proportional dependence of all model scales upon the unified gaugino mass M 1 / 2 in the No-Scale F - SU ( 5 ) model suggests one possible mechanism of confronting the electroweak fine-tuning problem.