1 research outputs found
Unifying gauge couplings at the string scale
Using the current precision electroweak data, we look for the minimal
particle content which is necessary to add to the standard model in order to
have a complete unification of gauge couplings and gravity at the weakly
coupled heterotic string scale. We find that the addition of a vector-like
fermion at an intermediate scale and a non-standard hypercharge normalization
are in general sufficient to achieve this goal at two-loop level. Requiring the
extra matter scale to be below the TeV scale, it is found that the addition of
three vector-like fermion doublets with a mass around 700 GeV yields a perfect
string-scale unification, provided that the affine levels are , as in the string-GUT. Furthermore,
if supersymmetry is broken at the unification scale, the Higgs mass is
predicted in the range 125 GeV - 170 GeV, depending on the precise values of
the top quark mass and parameter.Comment: 11 pages, 4 eps figures, using jpconf style, talk given at CORFU2005,
RTN meeting ``The Quest for Unification: Theory Confronts Experiment'', 11 -
18 September 2005, Corfu, Greec