imits

1. The imits et’s L S D N olutions peak about LSND Anomaly ew eutrinos in iscoveries elphi WIN’05 20th International Workshop on Weak Interactions and Neutrinos Delphi, Greece, June 6-11, 2005

2. THE FACTS

3. Standard results “Non Standard” results Neutrino disappearance Solar neutrino deficit 8 σ effect Atmospheric neutrino anomaly 14 σ effect Neutrino Oscillations Homestake, SAGE, GALLEX, SK, SNO + KamLAND SK and K2K sin213 < 0.047  m221 = (7.3 - 9.1) 10-5 eV2 sin212 = (0.23 – 0.37) | m231| = (1.4 – 3.3) 10-3 eV2 sin2 223 > 0.90 M. Maltoni et al., New J. Phys. 6:122, 2004

4. “Standard” results No neutrino disappearance • Bugey (e→ e) L = 15 m , 40 m, 95 m; E ~ few MeV → m2 ~ 0.01 – 1 eV2 • CHOOZ and Palo Verde (e→ e) [for 13 small] L ~ 1000 m; E ~ few MeV → m2 ~ 10-3 eV2 • CCFR (→ ) L = 0.715 km and 1.116 km (2 detectors) 40 GeV < E < 230 GeV → m2 ~ 10 – 100 eV2 • CDHS (→ ) L = 0.130 km and 0.835 km (2 detectors) E ~ GeV → m2 ~ 1 – 100 eV2

5. “Standard” results No neutrino appearance • NOMAD (→ e) L = 0.635 km; 1 GeV < E < 100 GeV → m2 ~ 1 – 100 eV2 • KARMEN (→ e) L = 17.6 m; 16 MeV < E < 50 MeV → m2 ~ 0.1 – 10 eV2 So far, so good! No short baseline neutrino “anomaly” Neutrino anomalies explained by oscillations between 3 neutrinos → 2 independent m2

6. Non-Standard result Neutrino appearance • LSND (→ e) L = 30 m; 20 MeV < E < 52.8 MeV → m2 ~ 1 – 10 eV2 It did see e appearance! But…  m2atm +  msol m2LSND

7. Neutrinos are produced from pion and muon decays + → + (e+e) - → - (e- e) + → e+e- → e-e e Most + decay at rest (97%) and also most + Very few - decays at rest (DAR) → 0.08% e backgrounds The LSND experiment A. Aguilar et al., Phys. Rev. D64:112007, 2001

8. e excess : 87.9 ± 22.4 ± 6.0 P ( → e ) = (0.264 ± 0.067 ± 0.045) % 3.3 σ effect A. Aguilar et al., Phys. Rev. D64:112007, 2001 G. Drexlin, Nucl.Phys.Proc.Suppl.118:146-153,2003

9. THE ESPECULATIONS

10. Classifying solutions • With and without sterile neutrinos • With one and with more than one sterile • With and without neutrino oscillations • With and without CPT violation • With non-standard and with standard processes • With and without extra dimensions • With problems and with problems • Those we like and those we don’t like • Those we have proposed and those we haven’t proposed • No solution But if LSND is right, all imply NEW PHYSICS!

11. 4 neutrino models 2+2 3+1 e   s  m2atm  m2LSND  m2LSND  m2atm  m2sol  m2sol Disfavored by SBL and atmospheric neutrino experiments Steriles would participate in solar and atmospheric neutrino oscillations Ruled out at 5.1 σ M. Maltoni et al., New J. Phys. 6:122, 2004

12. 3+2 neutrino models  m2LSND2  m2LSND1  m2atm  m2sol Compatibility between SBL (including KARMEN) and LSND of 30%, instead of 3.6 % in the standard 3+1 model M. Sorel, J. M. Conrad and M. H. Shaevitz, Phys. Rev. D66:033009,2002

13. m2LSND m2LSND,atm m2atm m2KamLAND The killer: reactor experiments The killer: atmospheric experiments Although there is some room for CPT violation with all-but-LSND data… • … for LSND m2, antineutrinos signal would • wash out the up-down asymmetry • produce a deficit of up-going muon events • near the horizon Bugey and CHOOZ: need Ue3' 1 G. Barenboim, L. Borissov and J. Lykken, hep-ph/0212116 A. Strumia, Phys. Lett. B539:91-101,2002 M. C. González-García, M. Maltoni and T. Schwetz, Phys. Rev. D68:053007, 2003 PKamLAND' 1 CPT violating spectra e   m2atm m2sol H. Murayama and T. Yanagida, Phys. Lett. B520:263-268, 2001 G.Barenboim, L. Borissov and J. Lykken, Phys.Lett.B534:106-113,2002

14. 4 neutrinos + CPT violation Assuming the same m2 for neutrinos and antineutrinos but different mixings • 3+1 models • - U 4 constrained by CCFR and atmospherics, not CDHS → still some room • - Ue4 constrained by GALLEX • (e disappearance during test with a 51Cr source) • 2+2 models • Too little sterile content on solar and • atmospheric neutrino oscillations → Ruled out • Hybrid models • (3+1) , (2+2) : no bound from solar neutrino data • (3+1) , (2+2) : similar to (2+2) → excluded V. Barger, D. Marfatia and K. Whisnant, Phys. Lett. B576:303-308,2003

15. Pure decoherence  Pure decoherence both Mixing + decoherence  Mixing + decoherence both CPT violating decoherence Quatum gravity models involve singular space-time configurations: space-time foam → decoherence is the result of particle propagation due to the fuzzy properties of the background not necessarily related to mass differences between particles and antiparticles Simple model: effects only in the antineutrino sector and diagonal decoherence matrix → No spectral distortions at KamLAND Without KamLAND With KamLAND G. Barenboim and N. E. Mavromatos, JHEP01:034, 2005

16. Lorentz violation In the minimal Standard Model Extension (SME) with Lorentz violation, neutrinos are massless and oscillations are determined by 102 real constants controlling the Lorentz violation V. A. Kostelecký and M. Mewes, Phys. Rev. D69:016005, 2004 P (→ e) ' |(heff)e|2 L2 → for LSND |(heff)e|2 ~ (3 x 10-19 GeV)2 aL ~ 10-19 GeV cL ~ 10-17 V. A. Kostelecký and M. Mewes, Phys. Rev. D70:076002, 2004 Unusual dependences for the oscillation phases: aL L and cL L E Predict, e.g., azimuthal dependence for atmospheric neutrinos Constraints (in the  -  sector): aL < few 10-23 GeV cL < 10-24 M. C. González-García and M. Maltoni. Phys. Rev. D70:033010, 2004

17. These models predict  = 0 for L = 2 decays → constrained by KARMEN BRKARMEN < 0.0017 (90% CL), but BRLSND > 0.0021 (90% CL) LFV muon decay The L = 2 decay: + → e+ + e +  ( = e, , ) could explain LSND data if K. S. Babu and S. Pakvasa, hep-ph/0204236 B. Armbruster et al., Phys. Rev. Lett. 90:181804, 2004 Scale of new physics relatively low,  ~ 300-400 GeV, → effects on low energy observables, e.g., the SM  parameter in the Michel spectrum Predicted  = 0.7485 TWIST experiment Measured  = 0.75080 ± 0.00032± 0.00097 ± 0.00023 J. R. Musser et al., Phys. Rev. Lett. 94:101805, 2005

18. Mass varying neutrinos Matter effects on neutrinos due to the interaction with a very light and weakly coupled scalar particle could give rise to masses and mixings which are enviroment dependent Yukawa couplings Nucleon number density V()´´ • LSND, KamLAND, K2K and Palo Verde are • in matter • Bugey and CHOOZ are in air • KARMEN is 50% in matter and 50% in air • CDHS is unknown • It could accomodate 3+1 models: an experiment • like Bugey but in matter should see disappearance • Limits for 2+2 models are very model dependent D. B. Kaplan, A. E. Nelson and N. Weiner, Phys. Rev. Lett. 93:091801, 2004 K. M. Zurek, JHEP 0410:058, 2004

19. Shortcuts in extra dimesions In some theories with extra dimensions, SM particles propagate only in the brane, but non-SM particles can also do it in the bulk. If the brane is distorted → shortcuts s travel “faster” This induces an effective term in the hamiltonian which introduces resonant mixing driven by , the aspect ratio of the brane deformation The key point: evading CDHS bounds by a resonance in the range 30 - 400 MeV No effect No bound If Eres ~ 30 – 100 MeV → no signal in MiniBooNE If Eres ~ 200 – 400 MeV → impressive signature in MiniBooNE H. Päs, S. Pakvasa and T. J. Weiler hep-ph/0504096

20. 3+1 model with a decay option… …but LSND explained (mainly) by oscillations Neutrino oscillations + decay The decay option: key ingredient to evade CDHS bounds For small U4 and short baselines CDHS compares measurements at two detectors: if D1 = D2 , no difference This requires 4 / m4 ~0.03-0.1 and m4 ~ few eV → g ~ 103 -104 In contradiction with laboratory bounds g < 10-2 E. Ma, G. Rajasekaran and I. Stancu, Phys. Rev. D61:071302, 2000

21. As far as ge´ Uel ghl 0 , we expect e and e appearance Neutrino decay 3+1 model with a decay option… …but LSND explained by decay Good fit to data SPR, S. Pascoli and T. Schwetz, hep-ph/0505216

22. LSND and KARMEN compatibility Mixing of e with 4 is not required → we set Ue4 = 0 Only CDHS and atmospherics constrain the model SPR, S. Pascoli and T. Schwetz, hep-ph/0505216

23. The rate of N’s is controlled by U 4 and that of e’s by ghe In order to be consistent with laboratory and supernova bounds, a typical value is g ~ 10-5 With -1 ~ LLSND (g m4 ~ 1 - 10 eV) → m4 ~ 100 keV In addition, extending the model with an extra neutrino and allowing for complex couplings, the signal in the neutrino run might be suppressed The MiniBooNE signal SPR, S. Pascoli and T. Schwetz, hep-ph/0505216

24. THE RIGHT ONE

25. ??

26. Conclusions • Solar (8σ) and atmospheric neutrino (14σ) anomalies well understood in terms of oscillations • LSND: the only (anti)neutrino appearance experiment with positive signal (3.3σ)… why shouldn’t it be right? • Many possible solutions… • … if LSND is right, (hopefully) one must be right • If so, we might need to forget about our prejudices on sacred principles, modify the Standard Model of Cosmology… • We all will have more fun! • If anyone is in a hurry…

27. …we could ask to Delphi’s Oracle Oracular responses were given every month, on the 7th day, the birthday of Apollo Unfortunately… So we will wait for MiniBooNE!