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CP violation in the neutrino sector

CP violation in the neutrino sector. Lecture 4: New sources of CP violation?. Walter Winter Nikhef, Amsterdam, 06.03.2014. Contents (overall). Lecture 1: Introduction to neutrino physics, sources of CP violation Lecture 2: Neutrino oscillations in vacuum, measurement of d CP

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CP violation in the neutrino sector

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  1. CP violation in the neutrino sector Lecture 4: New sources of CP violation? Walter Winter Nikhef, Amsterdam, 06.03.2014

  2. Contents (overall) • Lecture 1:Introduction to neutrino physics, sources of CP violation • Lecture 2:Neutrino oscillations in vacuum, measurement of dCP • Lecture 3:Matter effects in neutrino oscillations: “extrinsic CP violation” • Lecture 4:New sources of CP violation? References: • WW: “Lectures on neutrino phenomenology“, Nucl. Phys. Proc. Suppl. 203-204 (2010) 45-81 • Giunti, Kim: “Fundamentals of neutrino physics and astrophysics“, Oxford, 2007

  3. Contents (lecture 4) • Sterile neutrinos • Non-standard interactions+ Is it plausible that new physics shows up in neutrino sector only • Non-unitarity

  4. Sterile neutrinos

  5. Evidence for light sterile neutrinos?(addl. generations, not weakly interacting) • LSND/MiniBooNE • Reactor+gallium anomalies • Global fits (MiniBooNE @ Neutrino 2012) (B. Fleming, TAUP 2011) (Kopp, Maltoni, Schwetz, 1103.4570)

  6. Neutrino oscillations in vacuum Master formula: “mass squared difference“F(L,E)=L/E “spectral dependence“ For antineutrinos: U  U* Works for sterile neutrinos as well! At short distances: Only large mass squared terms non-vanishing

  7. Example: 3+1 framework, parameterization-independent • 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

  8. Again: Necessary conditions for the observation of CPV Since  need spectral info! Since for a=b need to observe flavor transitions Need (at least) three flavors(actually conclusion in quark sector by Kobayashi, Maskawa, Nobel Prize 2008) No CP violation in two flavor subspaces! Need to be sensitive to (at least) two mass squared splittings at the same time! Require at least two (light) sterile neutrinos; then new sources of CPV (but: do not really release tension in data …) ~ Jarlskog invariant

  9. Non-standard interactions

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

  11. Lepton flavor violation (d=6) Ex.: NSI 4n-NSI CLFV • Charged leptonflavor violation • Strongbounds 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?

  12. Gauge-inv. d=8 operator? • 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] Davidson, Pena-Garay, Rius, Santamaria, 2003 Project outneutrino field Project outneutrino field H, L: SU(2) doublets

  13. 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)

  14. On current NSI bounds • The bounds for the d=6 (e.g.scalar-mediated) operators are strong (CLFV, Lept. univ., etc.)(Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003) • The model-independent bounds are much weaker(Biggio, Blennow, Fernandez-Martinez, arXiv:0907.0097) • However: note that here the NSI have to come from d=8 (or loop d=6?) operators  e ~ (v/L)4 ~ 10-4 natural? • “NSI hierarchy problem“? t sector least constrained

  15. Source NSI with nt at a NuFact • Probably most interesting for near detectors: eets, emts (no intrinsic beam BG) • Near detectors measure zero-distance effect ~ |es|2 • Improving current bounds requires substantial equipment This correlation is always present if:- NSI from d=6 operators- No CLFV (Gavela et al,arXiv:0809.3451;see also Schwetz, Ohlsson, Zhang, arXiv:0909.0455 for a particular model) ND5: OPERA-like ND at d=1 km, 90% CL (Tang, Winter, arXiv:0903.3039)

  16. Other types of source NSI • In particular models, also other source NSI (without nt detection) are interesting • Example: (incoh.)eems from addl.Higgs triplet asseesaw (II) mediator 1 kt, 90% CL, perfect CID Geometric effects? Effects of std. oscillations Systematics(CID) limitation?CID important! Requires CID! (Malinsky, Ohlsson, Zhang, arXiv:0811.3346)

  17. CP violation in non-standard interactions • Discovery potential for new CP violation (WW, Phys.Lett. B671 (2009) 77)

  18. For what fraction of the phases can CPV be discovered? • If additional phases are present, the chances to discover CPV are good! (WW, Phys.Lett. B671 (2009) 77)

  19. Non-unitarity

  20. Non-unitarity of mixing matrix also: „MUV“ • Integrating out heavy fermion fields, 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 • Similar effect to NSI, but source, detector, and matter NSI are correlated in a particular, fundamental way (i.e., process-independent)

  21. Impact of near detector • Example: (Antusch, Blennow, Fernandez-Martinez, Lopez-Pavon, arXiv:0903.3986) • nt near detector important to detect zero-distance effect • Magnetization not mandatory, size matters Curves: 10kt, 1 kt, 100 t, no ND

  22. NSI versus NU • For a neutrino factory, leptonic NSI and NU may have very similar correlations between source and matter effects, e.g. NU (generic, any exp.) NSI (d=6, no CLFV, NF) • Difficult to disentangle with NuFact alone  SB? NU NSI (Meloni, Ohlsson, Winter, Zhang, JHEP 1004 (2010) 041)

  23. Is it possible/plausible that “new physics” shows up in the neutrino sector only? • Possible? • Yes, but at least non-standard four-fermion interactions require quite some fine-tuning • It is difficult to find models which would not produce effects elsewhere (LHC, EWPT, …) • Plausible?Additional sterile generations are perhaps the most plausible new physics effect: • Short-baseline anomalies (eV steriles)Caveat: would show up in cosmology … (problem or feature?) • Warm dark matter (keV steriles) • Non-unitarity (>> GeV steriles) • Leptogenesis (GUT-scale steriles)

  24. Summary • If no new physics will be found at the LHC, the lepton sector may still provide enough CP violation for successful leptogenesis • Most plausible candidates: see-saw mechanisms in different versions; no necessary implications at the TeV scale; basically “neutrino Standard Model(s)“ • Physics beyond the neutrino Standard Model may also provide new sources of CP violation; however: this kind of physics may have implications elsewhere • Most interesting candidate, perhaps: sterile neutrinos

  25. Discussion topics • Do neutrinos really oscillate? After all, the mass eigenstates travel with different velocities … • What happens over extremely long distances? Can one measure CP violation then? • Why are neutrino masses “physics beyond the Standard Model“? Are they? Really? • Why is there only one CP phase in the lepton mixing matrix, and three if neutrinos are Majorana particles? [after all, a general unitary matrix is parameterized including six phases] • What do we actually learn from neutrinoless double beta decay?

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