Neutrinos and the Flavour Puzzle: A Mini-Review Stefan Antusch Max-Planck-Institut für Physik (Werner-Heisenberg-Institut) University of Basel Department of Physics July 22, 2011Review talk at EPS-HEP 2011

Stefan Antusch University of Basel & MPI of Physik (Munich) The Neutrino Flavour Puzzles 2 Neutrino masses: Why so small? How to extend the SM? Lepton mixing: Why so large? (TB?)

Stefan Antusch University of Basel & MPI of Physik (Munich) Many open neutrino questions …  What are the values of θ 13, δ, sgn(Δm 31 2 )?  What is the absolute neutrino mass scale?  Are neutrino masses of Dirac or Majorana type?  If Majorana, what are the values of the Majorana phases?  Precise values of all leptonic mixing angles? 3 Such open questions are great! It means we can still make predictions... !

Stefan Antusch University of Basel & MPI of Physik (Munich) The Neutrino Flavour Puzzle #1 4 Neutrino masses: Why so small? How to extend the SM?

Stefan Antusch University of Basel & MPI of Physik (Munich) 5 mνmν MRMR ΣRΣR (type I or III) Is it a tree-level “Seesaw”? P. Minkowski ('77), Mohapatra, Senjanovic, Yanagida, Gell-Mann, Ramond, Slansky, Schechter, Valle, Magg, Wetterich, Ma, Foot, Lew, He, Joshi,... (A) At high scale (~ M GUT ) (B) At TeV scale (→ colliders, LHC) (C) At eV energies (light sterile ν’s)... in model building, most approaches are based on: At which scale?

Stefan Antusch University of Basel & MPI of Physik (Munich) 6 mνmν MRMR R Dirac neutrinos string theory ?... or something completely different

Stefan Antusch University of Basel & MPI of Physik (Munich) 7... to find answers we need to combine data from various sources: Colliders (LHC) 0νββ decay, Tritium β decay, cosmology indirect tests (e.g. LFV, universality, non-unitarity) → talk by Alessandro Strumia (tomorrow) Best chances for TeV scale mass generation:

Stefan Antusch University of Basel & MPI of Physik (Munich) The Neutrino Flavour Puzzle #2 8 Lepton mixing: Why so large? (TB?)

Stefan Antusch University of Basel & MPI of Physik (Munich) 9 I) Preliminary remark: S.A., Kersten, Lindner, Ratz (‘03) Large mixing is no fixed point of the RG evolution → There is no unbroken symmetry to enforce TB mixing! RGEs for the mixing angles (in LO):

Stefan Antusch University of Basel & MPI of Physik (Munich) 10 I) “Direct” models: Identify remnant symmetries! G Fam generated by S,T and U → S 4 family symmetry S 4 preferred: Lam A 4 possible as well for certain selection of field reps G Fam Neutrino Sector Charged Lepton Sector U TB Generator T broken but S,U preserved! Generators S, U broken but T preserved! Altarelli, Feruglio, Ma, Hagedorn, Merlo, Luhn...

Stefan Antusch University of Basel & MPI of Physik (Munich) 11 II) “Indirect” models: Dynamical fields = Flavons ~ A, B, C in 3 of G Fam generate flavour structure in the neutrino sector G Fam typically broken completely in m ν → vacuum alignment crucial ‘Direct’ vs. ‘indirect’ models: King, Luhn (‘09) King, Ross, de Medeiros Varzielas, Malinsky, Chen,...

Stefan Antusch University of Basel & MPI of Physik (Munich) 12 Both approaches point to non-Abelian discrete family symmetries G Fam ! Various successful models have been constructed by many authors (too many to review them all in a mini-review)...!

Stefan Antusch University of Basel & MPI of Physik (Munich) 13 Finally, if T2K gets confirmed: Is TB mixing still the right LO mixing pattern? T2K collaboration (2011) → talk by Michele Maltoni → talk by Claudio Gigante

Stefan Antusch University of Basel & MPI of Physik (Munich) 14 The flavour puzzle: (At least) four aspects

Stefan Antusch University of Basel & MPI of Physik (Munich) We should not forget the other pieces of the flavour puzzle! 15 I) The neutrino flavour puzzle III) The “new physics” flavour puzzle II) The SM flavour puzzle IV) The puzzle of CP violation

Stefan Antusch University of Basel & MPI of Physik (Munich) Example from the SM flavour puzzle: 16 Why are the masses of down-type quarks and charged leptons so similar?

Stefan Antusch University of Basel & MPI of Physik (Munich) Example from the SM flavour puzzle 17 (running masses at the top-mass scale; errors are 3 times the 1σ errors...) m b ↔ m τ ? m s ↔ m μ ?

Stefan Antusch University of Basel & MPI of Physik (Munich) Mass relations are predictions of unified models 18 → colliders! In SUSY GUTs the viability depends on SUSY parameters: [2] S.A., Spinrath (‘09)[1] Georgi, Jarlskog (‘79) [3] Allanach, King (‘96) [3] [1] [2] [3]

Stefan Antusch University of Basel & MPI of Physik (Munich) 19 MuMu MeMe MdMd mνmν GUT relation CP violation e.g.: U ν + = U TB

Stefan Antusch University of Basel & MPI of Physik (Munich) 20 More generally in GUTs, when charged lepton corrections dominate... MuMu MeMe MdMd mνmν GUT relations e.g.: U ν + = U TB 1) Prediction for θ 13 MNS (for ) Novel Clebsch factors for viable GUT mass relations → can lead to large θ 13 MNS (e.g. θ 13 MNS ≈ 7.6° or ≈ 10°) S.A., Maurer (’11)

Stefan Antusch University of Basel & MPI of Physik (Munich) 21 More generally in GUTs, when charged lepton corrections dominate... MuMu MeMe MdMd mνmν GUT relation e.g.: U ν + = U TB 2) Lepton mixing sum rule (for ) King (’05); Masina (’05); S.A., King (‘05)

Stefan Antusch University of Basel & MPI of Physik (Munich) 22 2) Lepton mixing sum rule (for ) from S.A., Huber, King, Schwetz (’07) → δ MNS ≈ 180°, θ 13 MNS ≈ 10° For large θ 13 MNS → δ MNS ≈ 90°,270°

Stefan Antusch University of Basel & MPI of Physik (Munich) 23  GUT symmetries unify “vertically”, family symmetries unify “horizontally” GUTs x Family symmetries are a poweful framework for approaching the flavour puzzle!

Stefan Antusch University of Basel & MPI of Physik (Munich) The flavour puzzle with “new physics” 24 What is the flavour structure of the new physics (if TeV energies)?

Stefan Antusch University of Basel & MPI of Physik (Munich) 25  Supersymmetry: For each SM particle there is a supersymmetric “partner particle”. SUSY is broken: The SUSY particles have their own flavour structure The flavour puzzle would get a “new dimension”: What is the flavour structure of the SUSY particles?

Stefan Antusch University of Basel & MPI of Physik (Munich) 26 Explain flavour structure in the SM, e.g.: Generate flavour stucture of the SUSY particles: Family symmetry! SUSY flavour structure related to the one of the SM Family symmetries: Can solve SUSY flavour problem! Abel, Khalil, Lebedev (’01) Ross, Vives (‘02), Ross, Velasco-Sevilla, Vives (‘04) S.A., King, Malinsky (‘07)... Remaining tension can be resolved in SUGRA: S.A., King, Ross, Malinsky (’08) In particular: Non-Abelian family symmetries!

Stefan Antusch University of Basel & MPI of Physik (Munich) 27 Flavour physics effects = “DNA“ of flavour models Altmanns- hofer, Buras, Gori, Paradisi, Straub (‘09)

Stefan Antusch University of Basel & MPI of Physik (Munich) The puzzle of CP violation 28 Why is the unitary triangle right-angled?

Stefan Antusch University of Basel & MPI of Physik (Munich) 29  The unitarity triangle: Fit to the experimental data Observation: The angle α ≈ 90°... just an accident?

Stefan Antusch University of Basel & MPI of Physik (Munich) 30  The unitarity triangle: Fit to the experimental data Observation: The angle α ≈ 90°... just an accident? → poster by Martin Spinrath Recent development: New unified flavour models with G Fam plus Z 2 or Z 4 shaping symmetries (& spont. CP viol.): → can explain α = 90° by realising the “phase sum rule” → δ MNS ∈ {0°,90°,180°,270°} S.A., King, Luhn, Spinrath (‘11)

Stefan Antusch University of Basel & MPI of Physik (Munich) Challenge for flavour models: Resolve all aspects of the flavour puzzle! 31 I) The neutrino flavour puzzle III) The “new physics” flavour puzzle II) The SM flavour puzzle IV) The puzzle of CP violation

Stefan Antusch University of Basel & MPI of Physik (Munich) 32 Thanks for your attention!