Browsing by Subject "Global Symmetries"

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  • Heikinheimo, Matti; Huitu, Katri; Keus, Venus; Koivunen, Niko (2019)
    The Froggatt-Nielsen mechanism is a well-motivated framework for generating the fermion mass hierarchy. This mechanism introduces flavons, complex scalars which are singlet under the Standard Model gauge symmetry and charged under a new global family symmetry. We make use of a leptophilic flavon to produce the charged lepton Yukawa matrix. The real part of the flavon mixes with the Higgs boson and introduces lepton flavour violating interactions which are bounded by experiment. The imaginary part of the flavon, , is a long-lived light particle, whose abundance is restricted by cosmological observations. For m<2m(e) where the decay of to charged leptons is kinematically forbidden, we identify allowed regions of m with respect to the vacuum expectation value of the flavon field where all experimental and cosmological constraints are satisfied.
  • Andersen, Jens O.; Brauner, Tomas; Hofmann, Christoph P.; Vuorinen, Aleksi (2014)
  • Alanne, Tommi; Franzosi, Diogo Buarque; Frandsen, Mads T.; Kristensen, Mette L. A.; Meroni, Aurora; Rosenlyst, Martin (2018)
    We study the phenomenology of partially composite-Higgs models where electroweak symmetry breaking is dynamically induced, and the Higgs is a mixture of a composite and an elementary state. The models considered have explicit realizations in terms of gauge-Yukawa theories with new strongly interacting fermions coupled to elementary scalars and allow for a very SM-like Higgs state. We study constraints on their parameter spaces from vacuum stability and perturbativity as well as from LHC results and find that requiring vacuum stability up to the compositeness scale already imposes relevant constraints. A small part of parameter space around the classically conformal limit is stable up to the Planck scale. This is however already strongly disfavored by LHC results. In different limits, the models realize both (partially) composite-Higgs and (bosonic) technicolor models and a dynamical extension of the fundamental Goldstone-Higgs model. Therefore, they provide a general framework for exploring the phenomenology of composite dynamics.
  • Huitu, Katri; Koivunen, Niko (2019)
    The models based on SU(3)C x SU(3)L x U(1)X gauge symmetry (331-models) have been advocated to explain the number of fermion families. These models place one quark family to a different representation than the other two. The traditional 331-models are plagued by scalar mediated quark flavour changing neutral currents (FCNC) at tree- level. So far there has been no concrete mechanisms to suppress these FCNCs in 331- models. Recently it has been shown that the Froggatt-Nielsen mechanism can be incorporated into the 331-setting in an economical fashion (FN331-model). The FN331-model explains both the number of fermion families in nature and their mass hierarchy simultaneously. In this work we study the Higgs mediated quark FCNCs in FN331-model. The flavour violating couplings of quarks are suppressed by the ratio of the SU(2)L x U(1)Y and SU(3)L x U(1)X breaking scales. We find that the SU(3)L x U(1)X -breaking scale can be as low as 5 TeV in order to pass the flavour bounds.