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Deppisch, F. F., Hati, C., Patra, S., Sarkar, U., & Valle, J. W. F. (2016). 331 models and grand unification: From minimal SU(5) to minimal SU(6). Phys. Lett. B, 762, 432–440.
Abstract: We consider the possibility of grand unification of the SU(3)(c) circle times SU(3)(L) circle times U(1)(X) model in an SU(6) gauge unification group. Two possibilities arise. Unlike other conventional grand unified theories, in SU(6) one can embed the 331 model as a subgroup such that different multiplets appear with different multiplicities. Such a scenario may emerge from the flux breaking of the unified group in an E(6) F-theory GUT. This provides new ways of achieving gauge coupling unification in 331 models while providing the radiative origin of neutrino masses. Alternatively, a sequential variant of the SU(3)(c) circle times SU(3)(L) circle times U(1)(X) model can fit within a minimal SU(6) grand unification, which in turn can be a natural E(6) subgroup. This minimal SU(6) embedding does not require any bulk exotics to account for the chiral families while allowing for a TeV scale SU(3)(c) circle times SU(3)(L) circle times U(1)(X) model with seesaw-type neutrino masses.
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Deppisch, F. F., Hirsch, M., & Pas, H. (2012). Neutrinoless double-beta decay and physics beyond the standard model. J. Phys. G, 39(12), 124007–23pp.
Abstract: Neutrinoless double-beta decay is the most powerful tool to probe not only for Majorana neutrino masses but for lepton number violating physics in general. We discuss relations between lepton number violation, double-beta decay and neutrino mass, review a general Lorentz-invariant parametrization of the double-beta decay rate, highlight a number of different new physics models showing how different mechanisms can trigger double-beta decay and, finally, discuss possibilities of discriminating and testing these models and mechanisms in complementary experiments.
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