Abstract
We consider six-dimensional supergravity with gauge group SO(10)×U(1)A, compactified on the orbifold T2/Z2. Three quark–lepton generations arise as zero modes of a bulk 16-plet due to magnetic flux of the anomalous U(1)A. Boundary conditions at the four fixed points break SO(10) to subgroups whose intersection is the Standard Model gauge group. The gauge and Higgs sector consist of “split” SO(10) multiplets. As a consequence of the U(1)A flux, squarks and sleptons are much heavier than gauge bosons, Higgs bosons, gauginos and higgsinos. We thus obtain a picture similar to “split supersymmetry”. The flavor structure of the quark and lepton mass matrices is determined by the symmetry breaking at the orbifold fixed points.
Highlights
Fermions and bosons play very different roles in the Standard Model
In the following we shall propose a model where this difference is explained by connecting GUT symmetry breaking and supersymmetry breaking: Scalar quarks and leptons are very heavy because they belong to complete GUT multiplets, whereas supersymmetry breaking is small for gauge and Higgs fields since they form incomplete GUT multiplets
Crucial ingredients are GUT symmetry breaking by Wilson lines [3], the generation of a fermion multiplicity by magnetic flux [4] and the associated breaking of supersymmetry [5]
Summary
Fermions and bosons play very different roles in the Standard Model. It is remarkable that quarks and leptons form three copies of complete multiplets of a grand unified (GUT) group, SU(5) or SO(10), whereas gauge and Higgs bosons are single, incomplete, “split” multiplets. Following [9,10], SO(10) [15,16] is unbroken at one orbifold fixed point and broken at the other three to standard SU(5) × U (1)X [17], the Pati–Salam group SU(4) × SU(2) × SU(2) [18] and flipped SU(5) × U (1)X [19,20], respectively The intersection of these groups is the Standard Model gauge group, and the zero modes of bulk fields uncharged under the anomalous U (1)A form N = 1 gauge and Higgs split multiplets. Since the focus of this paper is on the additional zero modes generated by bulk magnetic flux, we shall ignore the effects of SO(10) symmetry breaking on the fixed point anomalies in the following. A complete discussion will be given in [30]
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