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NEUTRINO MASS AND THE LHC

NEUTRINO MASS AND THE LHC. Ray Volkas School of Physics The University of Melbourne. @ RVolkas. CoEPP Workshop, Cairns, July 2013. Neutrino oscillations and mass Experimental discovery of neutrino oscillations The see-saw mechanisms Radiative neutrino mass generation Final remarks.

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NEUTRINO MASS AND THE LHC

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  1. NEUTRINO MASS AND THE LHC Ray Volkas School of Physics The University of Melbourne @RVolkas CoEPP Workshop, Cairns, July 2013

  2. Neutrino oscillations and mass Experimental discovery of neutrino oscillations The see-saw mechanisms Radiative neutrino mass generation Final remarks

  3. 1. NEUTRINO OSCILLATIONS AND MASS The neutrino flavour or interaction eigenstatesare not Hamiltonian eigenstates in general: mass estates m1, m2, m3 unitary mixing matrix

  4. Two flavour case for clarity: Say at t=0 a ne is produced by some weak interaction process: After time evolution: Suppose they are ultrarelativistic 3-momentum eigenstates:

  5. Probability that the state is nm is: Amplitude set by mixing angle Oscillation length set by Dm2/E=(m22-m12)/E For solar neutrinos, this formula is invalidated by the “matter effect” -- a refractive index effect for neutrinos.

  6. 2. EXPERIMENTAL DISCOVERY OF NEUTRINO OSCILLATIONS

  7. Solar neutrinos

  8. ppn Boronn Berylliumn

  9. Sudbury Neutrino Observatory (SNO) proves flavour conversion: Courtesy of SNO Collaboration

  10. SNO was a heavy water detector. It was sensitive to ne’s through charge-exchange deuteron dissociation: diagrams courtesy of SNO collaboration

  11. But, through Z-boson exchange, it was also sensitive to the TOTAL neutrino flux ne + nm + nt: Diagrams courtesy of SNO Collaboration

  12. Terrestrial confirmation from KAMLAND Integrated flux of anti-ne from Japanese (and Korean!) reactors Diagrams courtesy of KAMLAND collab.

  13. Atmospheric neutrinos Atmospheric neutrinos

  14. Cosmic rays hit upper atmosphere, produce pions and kaons. They decay to give neutrinos. Provided muons decay in time, you get 2:1 ratio of m to e type neutrinos.

  15. Super-K results

  16. Terrestrial confirmation: K2K

  17. Terrestrial confirmation: MINOS Long baseline experiment from Fermilab to the Soudan mine in northern Minnesota

  18. antineutrinos neutrinos

  19. MINOS has also provided strong evidence that nm’s oscillate into nt’s Neutral current measurement

  20. Reactor anti-νe disappearance and θ13 Daya Bay collaboration Also: Reno, Double-CHOOZ, T2K, MINOS

  21. Fogli et al: PRD86 (2012) 013012

  22. 3. THE SEE-SAW MECHANISMS Minimal standard model: No RH neutrinos means zero neutrino masses

  23. Dirac neutrinos: simply add like all the other fermions Possible, but (1) no explanation for why (2) RH neutrino Majorana mass terms are gauge invariant and thus can be in the Lagrangian

  24. Minkowski; Gell-Mann, Ramond, Slansky; Yanagida; Mohapatra and Senjanovic Type 1 see-saw: Dirac mass RH Majorana mass Neutrino mass matrix: For M >> m: 3 small evalues of magnitude mν=m2/M 3 large evalues of order M see-saw Majorana estates: Notoriously hard to test because N is mostly sterile to SM gauge interactions and also expected to be very massive

  25. Magg; Wetterich; Schechter; Valle; Lazarides; Shafi; Mohapatra; Senjanovic; Cheng; Li. Type 2 see-saw: Add Higgs triplet instead of RH neutrinos: Why small <Δ>? positive <H> induces linear term in Δ Weak and EM interactions: more testable

  26. Mass limits on charge-2 scalar. Depends on BR assumption. Eur.Phys.J. C72 (2012) 2244 Barberio, Hamano, Rodd

  27. Foot, Lew, He, Joshi Type 3 see-saw: ATLAS-CONF-2013-19 Barberio, Hamano, Ong

  28. Seesaw Models - a common thread: Dimension-5 Weinberg effective operator (1/M)LLHH (shorthand).

  29. 4. RADIATIVE NEUTRINO MASS GENERATION Start with the Weinberg operator and “open it up” – derive it in the low-energy limit of a renormalisable model – in all possible minimal ways. You will then systematically construct the three see-saw models. This procedure can be used for higher mass-dimension ΔL=2 effective operators. In principle, one can construct all possible minimal* models of Majorana neutrinos. All d>5 operators [except those of the form LLHH(H Hbar)n] produce neutrino mass only at loop-level. For success need 1-loop, 2-loop and maybe 3-loop scenarios. * Have to define “minimal” – there are always assumptions.

  30. d=detailed, b=brief B=Babu J=Julio L=Leung Z=Zee

  31. A=Angel dGJ=deGouvêa+Jenkins

  32. Doubly-charged scalar k Zee-Babu model Effective op Opening it up 2-loop nu mass diagram The previously shown ATLAS bounds on doubly-charged scalars coupling to RH charged leptons apply to this model as well.

  33. Angelic O11 model (Angel, Cai, Rodd, Schmidt, RV, nearly finished!) leptoquark scalar colour octet fermion ΔL=2 term

  34. Neutrino mass and mixing angles can be fitted with mf, mϕ ~ TeV and couplings 0.01-0.1. Need two generations of ϕ to get rank-2 neutrino mass matrix. Flavour violation bounds can be satisfied.

  35. 5. FINAL REMARKS • Neutrinos have mass. We don’t know Dirac • or Majorana, or the mechanism. • Conspicuously light: different mechanism? • The answer “probably” lies beyond the LHC, • but at the very least we should understand • what the LHC excludes.

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