We study gauge mediation of supersymmetry breaking in SU(5) supersymmetric grand unified theory with gauge fields as messengers. The generated soft supersymmetry breaking parameters lead to close to maximal mixing scenario for the Higgs mass and highly red
(Non-universal)NegativesquarksandsleptonsmassessquaredattheGUTscale:Gaugemessengercontributionalonetypicallyleadstothesquarksandsleptonstachy-onicattheGUTscale.However,thisdoesnotruleoutthetheoryandjustimplythatwemightliveinameta-stablevacuumratherthanthetruevacuum.Fromthediscussionof netuningwelearnedthatitactuallymightbemorenaturaltoliveinameta-stablevacuum.For0≤bG≤3,whichisthecaseinrealisticmodelsduetoa2|,m2<0,m2<0.non-minimalcontent,squarksareevenmorenegative,|m2q q |>|m ll
SizableA–terms:LargeA–termsisoneoftheuniquefeatureofgaugemessengermodelswhichisabsentintheusualgaugemediation.Inusualgaugemediation,thesofttri-lineartermsatthemessengerscalearezeroandaregeneratedonlybyRGrunning.HereAtissizableanditwillhelptoachieveclosetomaximalmixingscenario.
3.2ContributionfromGravityMediation
SincethemessengerscaleistheGUTscale,andthegaugemediationisaoneloope ect,thenaivelyestimatedsizeofgravitymediationinducedbynon-renormalizableoperators(suppressedbyMPl)iscomparabletothecontributionfromgaugemediation.Thetypicalscaleofgaugemediationis MSUSY,giveninEq.(3.1),andthetypicalsizeofgravity mediationism3/2= 3F .GravitytogaugemediationratioisthenMPl
m3/2√