Abstract
The string landscape suggests that the supersymmetry breaking scale can be high, and then the simplest low energy effective theory is the Standard Model (SM). We show that gauge coupling unification can be achieved at about 1016–17 GeV in the SM with suitable normalizations of the U(1)Y. Assuming grand unification scale supersymmetry breaking, we predict that the Higgs mass range is 127 GeV to 165 GeV, with the precise value strongly correlated with the top quark mass and SU(3)C gauge coupling. We also present 7-dimensional orbifold grand unified theories in which such normalizations for the U(1)Y and charge quantization can be realized.
Highlights
The string landscape suggests that the supersymmetry breaking scale can be high, and the simplest low energy effective theory is the Standard Model (SM)
Even if the gauge hierarchy problem can be solved by the string landscape proposal, there are still some limitations of the SM, for example, the lack of explanation of gauge coupling unification and charge quantization
Should the Higgs particle be the only new physics observed at the Large Hadron Collider (LHC) and the SM is confirmed as a low energy effective theory, an important question will be: can we achieve gauge coupling unification in the SM without introducing any extra multiplets between the weak and grand unified theory (GUT) scales [7] or having large threshold corrections [8]? As is well known, gauge coupling unification cannot be achieved in the SM if we choose the canonical normalization for the U (1)Y hypercharge interaction, i.e., the Georgi-Glashow SU (5) normalization [9]
Summary
The string landscape suggests that the supersymmetry breaking scale can be high, and the simplest low energy effective theory is the Standard Model (SM). Should the Higgs particle be the only new physics observed at the Large Hadron Collider (LHC) and the SM is confirmed as a low energy effective theory, an important question will be: can we achieve gauge coupling unification in the SM without introducing any extra multiplets between the weak and GUT scales [7] or having large threshold corrections [8]? The U (1)Y normalization need not be canonical in string model building [10, 11], orbifold GUTs [12, 13] and their deconstruction [14], and in 4D GUTs with product gauge groups: (1) In weakly coupled heterotic string theory, the gauge and gravitational couplings unify at tree level to form one dimensionless string coupling constant gstring [10]
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