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Unifying gauge couplings at the string scale

David Emmanuel-Costa·Ricardo Gonzalez Felipe
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Abstract

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 $(k_Y, k_2 ,k_3)=(13/3, 1, 2) $, as in the $SU(5) \times SU(5)$ 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 $\tan β$ parameter.

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David Emmanuel-Costa, Ricardo Gonzalez Felipe. 2006-06-01. Unifying gauge couplings at the string scale. https://doi.org/10.1088/1742-6596%2F53%2F1%2F043

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