Abstract
We study proton decay in a six-dimensional orbifold GUT model with gauge group SO(10)×U(1)A. Magnetic U(1)A flux in the compact dimensions determines the multiplicity of quark-lepton generations, and it also breaks supersymmetry by giving universal GUT scale masses to scalar quarks and leptons. The model can successfully account for quark and lepton masses and mixings. Our analysis of proton decay leads to the conclusion that the proton lifetime must be close to the current experimental lower bound. Moreover, we find that the branching ratios for the decay channels p → e+π0 and p → μ+π0 are of similar size, in fact the latter one can even be dominant. This is due to flavour non-diagonal couplings of heavy vector bosons together with large off-diagonal Higgs couplings, which appears to be a generic feature of flux compactifications.
Highlights
Six-dimensional (6D) models [22,23,24]
We study proton decay in a six-dimensional orbifold GUT model with gauge group SO(10)×U(1)A
The magnetic flux in the extra dimensions plays a twofold role, it generates the multiplicity of quark-lepton generations and it breaks supersymmetry [26] around the GUT scale
Summary
The considered 6D GUT model has been described in detail in [25, 27, 28]. The bulk gauge group is SO(10) × U(1)A. The 6D theory has six 16-plets two of which, ψ and χ, contain the three quark-lepton generations as zero-modes They yield as split multiplets a fourth set of quark and lepton SU(2)L singlets, uc, dc, nc, ec. The proton lifetime crucially depends on the compactification scale Mc, which is related to the scale of unification in higher-dimensional GUTs. In orbifold GUTs, where the GUT symmetry is broken at orbifold fixed points, gauge couplings unify only approximately at the compactification scale, and corrections due to massive vector-like split multiplets, brane kinetic terms and the field content of the higher-dimensional theory have to be taken into account to achieve unification of couplings at some cut-off-scale Λ > Mc. In the following we study the consistency between proton decay and constraints from gauge coupling unification
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