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Quark-Lepton Symmetry In 5D

Quark-Lepton Symmetry In 5D. Kristian McDonald University of Melbourne, Australia. Overview. QL symmetry is useful if you like split fermions Quartification is less arbitrary in 5D. Quark-Lepton Symmetry. SM is QL asymmetric Add leptons: E = ( e, e’ , e’’) Extend gauge group

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Quark-Lepton Symmetry In 5D

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  1. Quark-Lepton Symmetry In 5D Kristian McDonald University of Melbourne, Australia

  2. Overview QL symmetry is useful if you like split fermions Quartification is less arbitrary in 5D

  3. Quark-Lepton Symmetry • SM is QL asymmetric • Add leptons: E = ( e, e’ , e’’) • Extend gauge group • Can define QL symmetry:

  4. QL Symmetry In 5D • In 5D inherently extra dimensional techniques become available • Orbifold Compactification • Provides an alternative means to break gauge symmetries • Introduces an additional energy scale, 1/R • Mass of some gauge fields is governed by 1/R rather than a scalar VEV • Different collider phenomenology • Fermions: bulk or brane ?

  5. Split Fermions • Introduce a singlet scalar field with a kink VEV solution. • Fermions get localised at one of the scalar kinks.   L= x5 f>0 f<0 

  6. d  Q L u e QL Split Fermion Model • Let be odd under QL symmetry: • Thus fL= -fQ , fe= -fu , f= -fd and if fQ , fu , fd >0

  7. f ‹1›+g ‹2› f = 20 g = 0 f = 20 g = -1 f = 20 g = -2 f = 20 g = -4 f = 20 g = -4.5 f = 20 g = -3 f = 20 g = -5 ‹2› Two scalar kinks: L= (f 1+g 2)  • Suppress proton decay and obtain flavour but requires 36 new parameters in SM. ‹1›

  8. d d   u Q L L e Q u e QL Split Fermion Model • QL symmetry implies mu=me etc.unless quark and lepton profiles are different. • Choose 2to be even under QL: gQ , gu , gd >0, gL=gQ , ge=gu , g=gd

  9. Grand Unification • Can we unify with leptonic colour? • Can’t use: But:

  10. Break: Quartification In 4D Unification requires intermediate symmetry breaking scales Can unify via a number of routes both with and without

  11. HIGGS CONTENT • Want to have • 4 ways to go in successive stages • Eight Higgs multiplets, four gain VEVs • Intra-multiplet hierarchy

  12. Unification achieved but… • Complicated Higgs sector: • Large Higgs potential- lots of parameters • Intra-multiplet hierarchy • Arbitrary masses • 7 light Higgs doublets • If we remove Higgs sector these problems disappear. How? • Place theory on an orbifold

  13. ORBIFOLD BREAKING • Gauge fields in bulk • Under vector components have parities:

  14. BRANE BREAKING • Scalar fields localised on brane • Define • Boundary condition • In the limit • (+,+) fields • Zero mode of (+,+)R,l are shifted up by Mc. • Higgs fields have decoupled

  15. SU(3)q SU(2)L SU(2)l U(1)Y

  16. GAUGE COUPLING UNIFICATION • Mc~ 4 x 1014 GeV, MGUT~ 4 x 1016 GeV Only occurs for

  17. CONCLUSIONS • 5D QL symmetry is useful if you like split fermions • Suppress p-decay • Address flavor • Quartification allows for QL symmetric GUT • In 4D: multiple symmetry breaking routes, with and without remnant lepton color symmetry • Complicated Higgs sector • In 5D: unique route which demands • Higgsless limit

  18. Acknowledgements • Alison Demaria • Andrew Coulthurst • Ray Volkas and • Bruce McKellar from the University of Melbourne.

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