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Neutrino physics Lecture 2: Theory of neutrino mass, and physics BSM?

Neutrino physics Lecture 2: Theory of neutrino mass, and physics BSM?. Herbstschule für Hochenergiephysik Maria Laach 04-14.09.2012 Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Measuring neutrino mass The seesaw paradigm

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Neutrino physics Lecture 2: Theory of neutrino mass, and physics BSM?

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  1. Neutrino physicsLecture 2: Theory of neutrino mass, and physics BSM? Herbstschule für Hochenergiephysik Maria Laach 04-14.09.2012 Walter Winter Universität Würzburg TexPoint fonts used in EMF: AAAAAAAA

  2. Contents • Measuring neutrino mass • The seesaw paradigm • Neutrino mass models at the TeV scale:What ingredients do “natural” models need? • Is it possible that new physics shows up in the neutrino sector only? • How does the large q13 affect our understanding of (lepton) flavor? • Summary and conclusions

  3. Measuring neutrino mass

  4. Tritium end point experiments • Direct test of neutrino mass by decay kinematics • Current bound: 1/250.000 x me (2 eV) TINY! • Future experiment: KATRIN (Karlsruhe Tritium Neutrino Experiment)1/2.500.000 x me (0.2 eV) ~8800 km (Guido Drexlin, NOW 2008)

  5. e- W- n p Neutrinoless double beta decay… if the neutrino is ist own antiparticle, a Majorana neutrino! • Two times simple beta decay: • Neutrinoless double beta decay: e- e- 2 x n2 x e W- W- n n p p e- = Caveat: discovering 0nbb does not mean that one has actually seen Majorana neutrinos! 0 x n2 x e W- n p

  6. Cosmological tests • Example:Relativistic neutrinos damp the formation of structure • Essentially sensitive to sum of neutrino masses • Information from different cosmological datasets used in literature • Limit ~ eV (S. Hannestad) … might finally be used rule to out that neutrino physics in charge of 0nbb!

  7. The seesaw paradigm

  8. Why is the neutrino mass so small? • Why are the neutrinos morethan 250.000 times lighter than the electron? • Cannot be described in simple extensions of the Standard Model • Is the neutrino mass the lowest order perturbation of physics BSM? • Seesaw mechanism: Neutrino mass suppressed by heavy partner, which only exists in the early universe (GUT seesaw)? • Decay of MR origin of matter-antimatter-asymmetry? • CP violation? Test in neutrino oscillations! • Requires Majorana nature of neutrino!Test in neutrinoless double beta decay (0nbb) Other SM particles Heavy partner

  9. Effective field theories BSM physics described by effective operators in the low-E limit (gauge invariant): L: Scaleof new physics Neutrinomass(LNV) Leptonflavorviolation (LFV) But these are no fundamental theories (non-renormalizable operators). Idea: Investigate fundamental theories (TeV completions) systematically!

  10. Seesaw mechanism • Neutrino mass from d=5 (Weinberg) - Operator • Fundamental theories at tree level: • Neutrino mass ~ Y2 v2/L (type I, III see-saw) • For Y = O(1), v ~ 100 GeV: L ~ GUT scale • For L ~ TeV scale: Y << 10-5 • Interactions difficult to observe at LHC • Couplings “unnaturally“ small? H H ? Type II Type III Seesaw Type I L L

  11. Neutrino masses at the TeV scale? … and physics at the LHC …

  12. Neutrino masses at the TeV scale • Goals: • New physics scale “naturally“ at TeV scale(i.e., TeV scale not put in by hand) Testable at the LHC?! • Yukawa couplings of order one • Requires additional suppression mechanisms. The typical ones: • Radiative generation of neutrino mass (n loops) • Neutrino mass from higher than d=5 effective operator • Small lepton number violating contribution e (e.g. inverse see-saw, RPV SUSY models, …)

  13. Example (suppression 3): Type-II, inverse seesaw (Florian Bonnet@GGI Florence 2012)

  14. Additional suppression (mechanisms 1+2):Loops versus dimension Loop suppression, controlled by 1/(16 p2) Type I, II, IIseesaw Depends onmediators/int. Zee, 1980;Ma, 1998; … Tree 1-loop 2-loop d=5 Discrete symmetryto forbid d=5? Depends on scale:L > 4pv ~ 3 TeV? d=7 Suppression by d, controlled by 1/L2 d=8 d=11 How can I make sure that no lower order operators are generated?

  15. Example: Neutrino mass from higher dimensional operators • Approach: Use higher dimensional operators, e.g. • Leads to • Estimate: for L ~ 1 – 10 TeV and mn linear in Yukawas (worst case): • d = 9 sufficient if no other suppression mechanism • d = 7 sufficient if Yukawas ~ me/v ~ 10-6 allowed

  16. The loop issue H H • Loop d=5 contribution dominates for or L > 3 TeV • Conclusion: If assumed that d=7 leading, one effectively has to put L << 3 TeV by hand(see e.g. Babu, Nandi, Tavartkiladze, 2009) • Can one avoid this? H H H H Close loop L L L L H+ d=5 operator d=7 operator

  17. Forbid lower dim. operators • Define genuine d=D operator as leading contribution to neutrino mass with all operators d<D forbidden • Use new U(1) or discrete symmetry (“matter parity“) • Problem: H+H can never be charged under the new symmetry!  Need new fields! • The simplest possibilities are probably(e.g. Chen, de Gouvea, Dobrescu, hep-ph/0612017; Godoladze, Okada, Shafi, arXiv:0809.0703)(e.g. Babu, Nandi, hep-ph/9907213; Giudice, Lebedec, arXiv:0804.1753)

  18. Higher dim. operators in THDM Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076 • Simplest possibility (d=7): Z5 with e.g.(SUSY: Z3) SUSY:only this one(but: there canbe operators withthe scalar singletin the NMSSM) Same for d=9

  19. Systematic study of d=7 Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076 • Systematically decompose d=7 operator in all possible ways • Notation for mediators: Lorentz SU(2) Y=Q-I3

  20. Generalizations of see-saws Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076 • Generalizations of originial see-saws: Duplication of the original see-saws plus scalars • Type I (fermionic singlet) • Type II(scalar triplet) • Type III(fermionic triplet)Characteristics:Similar phenomenology!

  21. A SUSY example Krauss, Ota, Porod, Winter, Phys. Rev. D84 (2011) 115023 • Neutral fermion mass matrix after EWSB in basis 2 Flavor struct. by 3 2 1 1 Mass states: ni Fermionic doublets#17 from list Compare to “inverse see-saw“(suppression mechanism 3)if heavy doublets integrated out

  22. Test at the LHC? (example) Krauss, Ota, Porod, Winter, Phys. Rev. D84 (2011) 115023 • Test mediators • Test LFV • Test LNV compare

  23. Even higher suppression? Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076 Loop suppression, controlled by 1/(16 p2) Tree 1-loop 2-loop Switched off by discrete symmetry Switched off bydiscrete symmetry d=5 Strategies for higher loops:Farzan, Pascoli, Schmidt, arXiv:1208.2732 To beavoided d=7 Suppression by d, controlled by 1/L2 d=8 for L < 3 TeV d=11 Example 1: d=9 at tree level Physics at TeV scale with O(1) couplings Example 2: d=7 at two loop  Suppression mechanisms 1), 2), and 3)

  24. New physics in neutrino sector only? Most discussed options in literature: Light sterile neutrinos (aka: light SM singlets) Heavy SM singlets ( non-unitary mixings) Non-standard interactions (aka: flavor changing neutral currents)

  25. Evidence for sterile neutrinos? • LSND/MiniBooNE • Reactor+gallium anomalies • Global fits (MiniBooNE @ Neutrino 2012) (B. Fleming, TAUP 2011) (Kopp, Maltoni, Schwetz, 1103.4570)

  26. Example: 3+1 framework(with addl. Dm2 ~ 1 eV2) • Well known tension between appearance and disapp. data (appearance  disappearance in both channels) • Need one or more new experiments which can test • ne disappearance (Gallium, reactor anomalies) • nm disappearance (overconstrains 3+N frameworks) • ne-nm oscillations (LSND, MiniBooNE) • Neutrinos and antineutrinos separately (CP violation? Gallium vs reactor?) • Example: nuSTORM - Neutrinos from STORed Muons(LOI: arXiv:1206.0294) Summary of options: Appendix of white paper arXiv:1204.5379

  27. also: “MUV“ Non-unitarity of mixing matrix? • Integrating out heavy fermion fields (such as in a type-I TeV see-saw), one obtains neutrino mass and the d=6 operator (here: fermion singlets) • Re-diagonalizing and re-normalizing the kinetic terms of the neutrinos, one has • This can be described by an effective (non-unitary) mixing matrix e with N=(1+e) U • Relatively stroung bounds already, perhaps not so good candidate for future measurements(see e. g. Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003)

  28. Non-standard interactions • Typically described by effective four fermion interactions (here with leptons) • May lead to matter NSI (for g=d=e) • May also lead to source/detector NSI How plausible is a modelleading to such NSI(and showing up inneutrino sector only)?

  29. Lepton flavor violation (d=6) • Charged leptonflavor violation • Strongbounds Ex.: NSI 4n-NSI CLFV e m ne nm ne nm ne ne e e e e • Non-standard neutrino interact. • Effects in neutrino oscillations in matter • Non-standard int. with 4n • Effects in environments with high neutrino densities (supernovae) BUT: These phenomena are not independent (SU(2) gauge invariance!)Is it possible that new physics is present in the neutrino sector only?

  30. Idea: d=8 operator? Davidson, Pena-Garay, Rius, Santamaria, 2003 • Decouple CLFV and NSI by SU(2) symmetry breaking with operator • Works at effective operator level, but are there theories allowing that? [at tree level] Project outneutrino field Project outneutrino field

  31. Systematic analysis for d=8 Feynman diagrams Basis (Berezhiani, Rossi, 2001) • Decompose all d=8 leptonic operators systematically • The bounds on individual operators from non-unitarity, EWPT, … are very strong! (Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003) • Need at least two mediator fields plus a number of cancellation conditions(Gavela, Hernandez, Ota, Winter, Phys. Rev. D79 (2009) 013007) Avoid CLFVat d=8:C1LEH=C3LEH Combinedifferentbasis elements C1LEH, C3LEH Canceld=8CLFV But these mediators cause d=6 effects Additional cancellation condition(Buchmüller/Wyler – basis)

  32. Implications of large q13: flavor

  33. Short seesaw-I mixing primer Block diag. Charged leptonmass terms Eff. neutrinomass terms cf., charged current Rotates left-handed fields

  34. The TBM “prejudice“ • Tri-bimaximal mixings probably most discussed approach for neutrinos (Ul often diagonal) • Can be obtained in flavor symmetry models (e.g., A4, S4) • Consequence: q13=0  Obviously not! • Ways out for large q13?

  35. Impact on theory of flavor? q13 ? very small very large Structure:A4, S4, TBM, … Anarchy:Random draw? vs. Some structure + randomness:Froggatt-Nielsen? Corrections?CL sector?RGR running? e.g. q12 = 35 + q13cosd(Antusch, King) Quark-leptoncompementarity:q13 ~ qC? Different flavor symmetry?

  36. Anarchy? • Idea: perhaps the mixing parameters are a “random draw“? • Challenge: define parameterization-independent measure • Result: large q13 “natural“, no magic needed (Hall, Murayama, Weiner, 2000; de Gouvea, Murayama, 2003, 2012)

  37. “Structure+randomness“:Froggatt Nielsen mechanism? (F. Plentinger) • YL/R are SM fermions • After integrating out the heavy fermions: • Integer power n is controlled by the (generation/flavor-dependent) quantum numbers of the fermions under the flavor symmetry • K: (complex) generation dependent (random) order one coefficients • Well-suited to describe hierarchies Example: Ml~

  38. Hybrid alternatives? Meloni, Plentinger, Winter, PLB 699 (2011) 244 Charged leptons:Strong hierarchy,masses throughSM Yukawas Quarks:Strong hierarchiesSmall mixings Neutrinos:Mild (no?) hierarchy,large mixings, Majorana masses? Origin:physics BSM?LNV operator?  q13=0 Ansatz suitablefor hierarchies,such as Froggatt-Nielsen? Flavor symmetry,structure?Tri-bimaximal mixing“paradigm“?

  39. Consequences • Can control the size of q13 by suitable U(1) charges/mass texture for the charged lepton sector: • Challenge: • Deviations from TBM q12 typically accompanied by large q13 • Re-think zeroth order paradigm (TBM)??? Meloni, Plentinger, Winter, PLB 699 (2011) 244

  40. Summary and outlook • Are neutrinos masses evidence for physics BSM? • Neutrinoless double beta decay • Tests at the LHC • 0nbb signal + CPV in lepton sector + no evidence for n mass at the LHC • GUT seesaw, leptogenesis? • Natural TeV neutrino mass model requires additional suppression mechanism; then, however, plausible to discover it at the LHC • Most likely case for new physics in neutrino sector: fourth generation (light sterile neutrino)? • Theory of flavor has to be re-thought after q13 discovery

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