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String unification scale and the hyper-charge Kac-Moody level in the non-supersymmetric standard model

Gi-Chol Cho·Kaoru Hagiwara
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Abstract

The string theory predicts the unification of the gauge couplings and gravity. The minimal supersymmetric Standard Model, however, gives the unification scale $\sim 2\times 10^{16}$ GeV which is significantly smaller than the string scale $\sim 5\times 10^{17}$ GeV of the weak coupling heterotic string theory. We study the unification scale of the non-supersymmetric minimal Standard Model quantitatively at the two-loop level. We find that the unification scale should be at most $\sim 4\times 10^{16}$ GeV and the desired Kac-Moody level of the hyper-charge coupling should be $1.33 \lsim \ky \lsim 1.35$ in the absence of significant string threshold effects.

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Gi-Chol Cho, Kaoru Hagiwara. 1997-11-26. String unification scale and the hyper-charge Kac-Moody level in the non-supersymmetric standard model. https://doi.org/10.1016/s0370-2693(97)01488-3

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