Abstract
Intersecting D-brane models in string theory can naturally support the gauge and matter content of left-right symmetric extensions of the Standard Model with gauge symmetry SU(3)_c x SU(2)_L x SU(2)_R x U(1)_{B-L}. Considering such models as candidates for explaining the 2TeV excesses seen in Run-1 by both ATLAS and CMS, the minimal possible scale of supersymmetry breaking is determined by the requirement of precise one-loop gauge coupling unification. For the vector-like, bifundamental and (anti-)symmetric Higgs content of such brane configurations, this comes out fairly universally at around 19TeV. For the SU(2)_R gauge coupling one finds values 0.48<g_R(M_R)<0.6. Threshold corrections can potentially lower the scale of supersymmetry breaking.
Highlights
Intersecting D-brane models in string theory can naturally support the gauge and matter content of left-right symmetric extensions of the Standard Model with gauge symmetry SU(3)c × SU(2)L × SU(2)R × U(1)B−L. Considering such models as candidates for explaining the 2 TeV excesses seen in Run-1 by both ATLAS and CMS, the minimal possible scale of supersymmetry breaking is determined by the requirement of precise oneloop gauge coupling unification
Since in controllable models of string theory, supersymmetry needs to be broken at a scale MSUSY smaller than the string scale MS ∼ MU, we consider the hierarchy of mass scales MZ < MR < MSUSY < MU and analyze the issue of gauge coupling unification
This letter is organized as follows: in section 2, we review a few important aspects of intersecting D-brane models where in particular we discuss under what circumstance one can still get gauge coupling unification at the string scale
Summary
Let us review some of the main ingredients for the construction of intersecting D7-brane models in orientifolds of the Type IIB superstring. Stacks of Na D7-branes can wrap holomorphic four-cycles Σa in the homology class H4(X, Z) of the threefold These D7-branes can carry a non-trivial gauge flux determining a line bundle La on Σa. Note that for all branes wrapping the same 4-cycle, the differences among the gauge couplings ga come only from the line bundles and only from the value of Σa c21(La) ∈ Z.3. If some of the branes are of SP -type due to the factor κ = 2 in (2.4), the SP branes should wrap a different four-cycle ΣSP than the U(N ) branes ΣU with τSP = 2τU In this case, one gets approximate gauge coupling unification in the sense just explained for U(N ) stacks. The initial brane realization should be supersymmetric at the string scale, where, as usual, supersymmetry breaking will be mediated to the observable sector by generating soft masses of the order MSUSY
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